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Mill-Max 3169-0-00-15-00-00-03-0 PCB Pins

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These are brand-new Mill-Max 3169-0-00-15-00-00-03-0 gold-plated PCB pins. They have an 0.018″ diameter tail (the standard size for a DIP pin) an 0.056″ diameter middle section and an 0.022″ diameter head. These are the pins that are used in my HP reproduction 8601A hybrid modules (available here), but are also useful in a wide variety of applications. Download the Mill-Max catalog page for this product here.


HP 1820-0285 Reproduction Pulse Shaper for 8007A and 8007B Pulse Generators

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Do you have an HP 8007 series pulse generator which no longer produces output? Unfortunately, the problem is likely one of the custom HP pulse shaper ICs, a part which is completely unavailable… That is until now! I have reverse-engineered the original IC and created a modern replacement using surface-mount components on a 4-layer PCB.

Because they use the original HP circuit, these parts function nearly identically to the originals and thus, barring another problem with your instrument, will allow it to easily meet factory specifications and easily pass the performance test printed in the manual. Look at the pictures which compare the positive and negative output pulses of an original part to this reproduction to see for yourself how well these work!

Not only do these parts work equivalently to the originals, they offer another distinct advantage – serviceability. Each unit comes with a service manual including a parts list, component placement diagram and schematic for easy troubleshooting and repair. That said, they use top quality NXP and Vishey parts for long life and come with my standard lifetime guarantee. If the unit ever fails to meet specification, just send it back to me for a free repair.

If you are interested in the story behind the development of these parts, please read my plug post here.

Download the schematic and PCB layout for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files. If you want to view the simulations you will also need LTSPICE which can be found at http://www.linear.com/designtools/software/.

EPROM Programmer Universal Adapter

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Are you trying to troubleshoot a vintage computer, gaming, or arcade system? Are you having trouble reading or testing the obsolete and obscure types of ROM or EPROM chips that it uses? Well, if so this is the adapter you need. Used in conjunction with an inexpensive Willem EPROM reader / programmer available elsewhere on eBay for as little as $30, this adapter will allow you to read virtually any ROM chip used in vintage equipment!

Note that this adapter does not support programming of any EPROM.

For example, this adapter is the perfect solution for testing the MPS6540 ROMs in a Commodore PET 2001 computer prior to buying one of my 6540 ROM adapters.

Included:
1x EPROM Programmer Universal Adapter
1x Set of jumper leads
1x Instruction manual

For more information, read the complete directions. They can be downloaded here.

Download the schematic and PCB layout for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files.

Commodore PET Video Mixer

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This tiny adapter allows the original PET 2001-8 computer to put out a rough approximation of composite video so that you can connect a standard composite video monitor in place of the internal monitor. (Just to be clear a composite video monitor is one which uses a single RCA jack for video input like is done for connecting a VCR to a TV.) This is useful for PETs missing their display section and, more importantly, for troubleshooting. Turning the PET monitor on and off in short succession can damage it and so I strongly recommend that you use one of my adapters and a standard composite video monitor with the internal monitor disconnected when troubleshooting a PET. These same adapters may also work in some other early computer equipment like the TRS-80 model 4, Z-19 data terminal and other all-in-one computers and terminals from the 1970’s-1980’s, but I haven’t tried it yet. If you do, please let me know.

Please note that this adepter may not work with all digital LCD based TVs and monitors. It is intended only for use with analog CRT-based displays such as would have been used when the PET was made.

The mixer plugs into the main-board of the PET in place of the video cable for the monitor but also requires a connection to one of the +5v lines on the board. The photos show the correct connection, which can be done with an alligator clip, thus avoiding soldering anything to the PET motherboard.

Download the schematic and PCB layout for this product here. Note that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files.

My design is a modification of one released by the Commodore PET Users Club of England. A copy of the schematic of their adapter is available here.

Commodore PET 2001 ‘Chiclet’ Key Plunger

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Do you have an original Commodore PET 2001 (‘chiclet’ keyboard model) with a broken-off key? If so, this is the part you need to fix it! When a key is broken off, the part that actually fails is the key plunger inside the keyboard, so this is the part you need to replace. The only tricky part of replacing it is removing the broken off piece of the old plunger from the keycap. I recommend doing this by drilling a tiny hole in the broken piece and then inserting a small screw in the hole to pull out the broken part.

This product is available for sale directly from Shapeways. Please order from the D’Asaro Designs Shapeways Store.

Download the STL file for this product here. Note that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files.

Batten and Allen BA3760 Dill Leadframe (DIP PCB Edge Clip Pins)

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For sale is one lot of 50 Batten and Allen BA3760 pins.

After much work tracking down a source for these amazing pins, I can finally make these available to the public! What makes these pins so special? Simple. They allow you to build a module out of a piece of standard 0.062″ thick PCB that will fit into all available DIP socket designs without damage to the socket. For this reason, I use them in many of my IC replacement products, such as the new version of my MPS-6540 ROM Adapter. For the details read on.

The pins on a DIP chip are a very precise form factor of 0.01″ thick and 0.02″ wide. DIP sockets are made to accept pins of this specific proportion and will not work well with pins of other proportions. Worse, many are damaged if pins which are thicker then 0.01″ are inserted into them. To the best of my knowledge, all commercial through-hole headers use either round pins or square pins, and none have pins with the specific proportions of a DIP pin.  To complicate matters, many older DIP sockets have side-walls which run into the plastic part of through-hole headers, preventing there use at all. The solution? PCB edge clip pins like these. Rather then passing through the PCB, these pins clip onto its edges providing a form-factor that almost exactly mimics that of a brazed ceramic DIP package.

Use these pins for:
– Replacing broken pins on a variety of my ROM and other IC replacement products
– Building one of my products yourself (remember: personal use only without my prior consent)
– Replacing broken pins on a BASIC Stamp board (they use a thinner PCB, so you will need to bend these slightly to get them to fit snugly).
– Building your own IC replacements or other projects that need to fit into DIP sockets

Download the datasheet for these pins with all the dimensions here.

6540 ROM Adapter (Old Version)

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This is the first revision of the Commodore PET ROM adapter. It is now obsolete, so unless you have a specific need for this version, please buy the new version here.

This adapter will replace a single MOS Technologies MPS6540 ROM chip. Included in the price is the needed 2716 ROM chip, programmed with the code you need. Please specify the full part number of the original chip when ordering so that I can program the replacement correctly.

PLEASE NOTE: These adapters will ONLY work to replace a chip with a part number starting with 6540. They will NOT replace types 2332, 2316, or other ROM types used in Commodore computers other than the original Commodore PET 2001. If you don’t know if you have a bad ROM chip, or if you don’t know which one is bad, you may be interested in my EPROM Programmer Universal Adapter which, when used in conjunction with an inexpensive Willem EPROM programmer, will allow you to read (and therefore test) an MPS6540 ROM chip.

These adapters replace MOS Technologies proprietary ROM chips with standard 2716 ROM chips and have the following features. They:
1) Are exact electrical replacements for the MPS6540 (except that they do not require a clock signal.) All five chip select lines are fully functional.
2) Have a small enough footprint that the adapters can replace any or all of the ROM chips in a PET 2001.
3) Use only parts that were available in 1977 and so they will not look out of place in a PET.

The one disadvantage of these adapters is that with a 2716 inserted they are about 0.4″ taller than the original 6540 chip and thus may not be mechanically compatible with all 3rd party expansion boards. Please make the appropriate measurements before ordering.

Download the schematic and PCB layout for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files.


How the Adapters Work

There are three fundamental electrical differences between the 2716 EPROM, designed by Intel and second sourced by everyone under the sun including the Soviets, and the MOS/Commodore proprietary MPS6540 ROM. These are:
1) The Pinouts are very different. The data and address lines are mapped to completely different pins on the two chips. In fact, the 2716 is in a 24 pin package and the 6540 is in a 28 pin package.
2) The 6540 has five chip select lines. CS3, CS4, and CS5 are active low meaning that they must be held low (+0v) for the chip to be on (its data lines to be low impedance). CS1 and CS2 are active high, meaning that they are must be high (+5v) for the chip to be on. The 2716 has only one chip select line and it is active low. However, the 2716 also has a standby low power mode which is turned on by bringing pin 18 (EP) high. Putting the chip into and out of this mode takes no more time than deselecting it and selecting it with the chip select line, so the EP line can be used exactly like a second active low chip select. 3) The MOS 6540 requires a clock signal and the 2716 does not. This is not really a problem, at least not in the PET, because the board does not rely on the chip only changing its data lines when it sees a clock pulse.

Implementing the Chip Select Lines

Correcting the pinout problem simply means connecting the wires up in the right way. This is trivial in principle but it took some work to make it all fit on the tiny board. The chip select lines are harder. In order to emulate the five chip select lines with only two the following logic needed to be implemented:

2716_CS = 6540_CS3 OR 6540_CS4 OR 6540_CS5
2716_EP = NOT (6540_CS1 AND 6540_CS2)

I could not find a way to implement this logic using only a single 74 series chip, and I did not really have room on the board for one anyway. I was going to use Fairchild TinyLogic instead, but I knew that surface mount components would look out of place in a 1977 computer. In the end I implemented it using discrete components, specifically, five 1n914 didoes, two 10k resistors, one 1k resistor, and a single 2n7000 transistor (for the NOT gate.)

Mechanical Considerations

The ROM chips in a Commodore pet are spaced so close together that the only way to fit more than one replacement side-by-side is to have the 2716 sitting exactly above the 6540 socket. Because the pinouts are incompatible this meant that I had to put two board on top of each other connected by a header. The upper board has the socket for the 2716 on it and the lower socket has the pins on it which plug into the 6540 socket. The header which connects the sockets carries the signals between them and spaces the two boards far enough apart that the resistors and diodes can fit between them, protected and out of sight. Because the 2716 has only 24 pins instead of 28, there is room on the end of the top board for the transistor. Putting the pins on the lower board was somewhat of a challenge as well. Dip pins are rectangular in shape and are, at their widest, 0.018″-0.020″ across. Header pins are on the order of 0.030″ and so will not fit into a DIP socket. MilMax sells header with 0.018″ pins but they are exorbitantly expensive at $10 per header and add ~0.1″ of wasted height to the adapter. After much consideration, I made the pins using 24 gauge bus bar wire. After placing the lower board over an actual Commodore PET ROM socket I pushed a strand of bus bar wire into each hole and then cut it off flush with a pair of quality Edsyn wire cutters. I then soldered each wire in. See the pictures and board layout above to see how it all turned out. The end result is an adapter which has no larger a footprint than an original 6540, but which is somewhat taller.

Some useful resources:
2716 Datasheet
6540 Pinout

2801Prog Rev. 1 MCM2801 EEPROM Programmer

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The 2801Prog is a compact, low-cost programmer for the Motorola MCM2801P (2801) EEPROM. The 2801 is a first-generation EEPROM requiring a high voltage (+25V) for programming and thus is not supported by commercial ‘universal’ programmers. However, it was widely used in its day and thus a reliable method of reading and programming it is required for the maintenance of legacy equipment.

For example, the 2801 is used to store the model differentiation and calibration data for the Mettler PE series of balances that are still widely used in laboratories around the world. As these chips age, the stored data is eventually lost and without it the scale will only display ‘ERROR’. While the data itself is widely available (see here for example) before the 2801Prog no commercial programmer supported the 2801 EEPROM and thus there was no easy way of fixing the balances. However, with the 2801Prog it is a simple matter of point-and-click.

This programmer connects to any computer with a 9600 baud RS-232 port and a terminal emulator and allows reading, verifying, and programming of the 2801 EEPROM. Also, gEEProg, a Python application for Macintosh, Windows, and Linux is  available which allows access to all programmer functions via a GUI. The gEEProg application is available for download farther down this page.

Included:
1x 2801Prog Rev. 1 EEPROM Programmer
1x Power Adapter
1x DB-9 RS-232 Cable

Note:
Hard copies of the manual and software are not included – they can be downloaded at the links below
Download the 2801Prog Rev. 1 manual here
Download gEEProg and the gEEProg manual here
Download the MCM2801 datasheet here

Note 2:
After selling out of the original, Rev. 0, version of the 2801Prog, I have updated the board, ROM, and GUI application and am now selling a new Rev. 1 version. This new version features a ZIF socket on the side of the board instead of the middle which makes actuating the release lever much easier. It also fixes several small hardware and software bugs. The original Rev. 0 is obsolete and no longer available for sale, but its documentation, photos, and build files are preserved here for those who want them. Note also that the new gEEProg application replaces the 2801Prog GUI application that shipped with the Rev. 0 2801Prog. gEEprog works with all versions of the 2801Prog as well as all other D’Asaro Designs Programmers.

Download the schematic, PCB layout, parts list, and source code for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files. Also, MPLABX (available from microchip.com) will be useful when opening the project file containing the source code.


2801Prog MCM2801 EEPROM Programmer (Obsolete Rev. 0)

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This is the now obsolete 2801Prog Rev. 0. This page is left here only to support for existing 2801Prog Rev. 0 owners. New customers should buy the 2801Prog Rev. 1 here.

The 2801Prog is a compact, low-cost programmer for the Motorola MCM2801P (2801) EEPROM. The 2801 is a first-generation EEPROM requiring a high voltage (+25V) for programming and thus is not supported by commercial ‘universal’ programmers. However, it was widely used in its day and thus a reliable method of reading and programming it is required for the maintenance of legacy equipment.

For example, the 2801 is used to store the model differentiation and calibration data for the Mettler PE series of balances that are still widely used in laboratories around the world. As these chips age, the stored data is eventually lost and without it the scale will only display ‘ERROR’. While the data itself is widely available (see here for example) before the 2801Prog no commercial programmer supported the 2801 EEPROM and thus there was no easy way of fixing the balances. However, with the 2801Prog it is a simple matter of point-and-click.

This programmer connects to any computer with a 9600 baud RS-232 port and a terminal emulator and allows reading, verifying, and programming of the 2801 EEPROM. A (Python) application for Macintosh, Windows, and Linux is also available which allows access to all programmer functions via a GUI. This application is available for download farther down this page.

Included:
1x 2801Prog EEPROM Programmer
1x Power Adapter
1x DB-9 RS-232 Cable

Note:
Hard copies of the manual and software are not included – they can be downloaded at the links below
Download the manual here
Download the GUI application here
The GUI application at the above link shipped with the Rev. 0 2801Prog but it is now obsolete and has been replaced with the new gEEProg application. gEEProg is compatible with all D’Asaro Designs programmers including the 2801Prog Rev. 0. Please consider upgrading.
Download gEEProg here
Download the MCM2801 datasheet here

Download the schematic, PCB layout, parts list, and source code for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files. Also, MPLABX (available from microchip.com) will be needed to open the project file containing the source code.

2006Prog SDA-2006 EEPROM Programmer

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The 2006Prog is a compact, low-cost programmer for the Siemens SDA-2006 (2006) EEPROM. The 2006 is a first-generation EEPROM requiring multiple high voltage supplies (+33V and +15V) and one negative voltage supply (-5V) for programming and thus is not supported by commercial ‘universal’ programmers. However, a reliable method of reading and programming it is required for the maintenance of legacy equipment.

For example, the 2006 is used to store the model differentiation and calibration data for the Sartorius MP8 series of balances that are still widely used in laboratories around the world. As these chips age the stored data is eventually lost and without it the balance will not work. Before the introduction of the 2006Prog no commercial programmer supported the 2006 EEPROM and thus there was no easy way of fixing the balances or backing up the data in the EEPROMs. Since the EEPROM data for these scales is not available on line,  if your laboratory uses Sartorius MP8 series balances, it would be a worthy investment to buy a 2006Prog for the explicit purpose of backing up the contents of the SDA-2006 EEPROMs. If you have a copy of the data, with the 2006Prog it is a simple matter of point-and-click to restore it to a chip.

This programmer connects to any computer with a 9600 baud RS-232 port and a terminal emulator and allows reading, verifying, and programming of the 2801 EEPROM. Also, gEEProg, a Python application for Macintosh, Windows, and Linux is  available which allows access to all programmer functions via a GUI. The gEEProg application is available for download farther down this page.

Included:
1x 2006Prog EEPROM Programmer
1x Power Adapter
1x DB-9 RS-232 Cable

Note:
Hard copies of the manual and software are not included – they can be downloaded at the links below
Download the 2006Prog manual here
Download gEEProg and the gEEProg manual here
Download my translation (from the original German) of the SDA-2006 datasheet here

Download the schematic, PCB layout, parts list, and source code for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files. Also, MPLABX (available from microchip.com) will be useful when opening the project file containing the source code.

2006Prog SDA-2006 EEPROM Programmer (Obsolete Rev. 0)

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The 2006Prog is a compact, low-cost programmer for the Siemens SDA-2006 (2006) EEPROM. The 2006 is a first-generation EEPROM requiring multiple high voltage supplies (+33V and +15V) and one negative voltage supply (-5V) for programming and thus is not supported by commercial ‘universal’ programmers. However, a reliable method of reading and programming it is required for the maintenance of legacy equipment.

For example, the 2006 is used to store the model differentiation and calibration data for the Sartorius MP8 series of balances that are still widely used in laboratories around the world. As these chips age the stored data is eventually lost and without it the balance will not work. Before the introduction of the 2006Prog no commercial programmer supported the 2006 EEPROM and thus there was no easy way of fixing the balances or backing up the data in the EEPROMs. Since the EEPROM data for these scales is not available on line,  if your laboratory uses Sartorius MP8 series balances, it would be a worthy investment to buy a 2006Prog for the explicit purpose of backing up the contents of the SDA-2006 EEPROMs. If you have a copy of the data, with the 2006Prog it is a simple matter of point-and-click to restore it to a chip.

This programmer connects to any computer with a 9600 baud RS-232 port and a terminal emulator and allows reading, verifying, and programming of the 2801 EEPROM. Also, gEEProg, a Python application for Macintosh, Windows, and Linux is  available which allows access to all programmer functions via a GUI. The gEEProg application is available for download farther down this page.

Included:
1x 2006Prog EEPROM Programmer
1x Power Adapter
1x DB-9 RS-232 Cable

Note:
Hard copies of the manual and software are not included – they can be downloaded at the links below
Download the 2006Prog manual here
Download gEEProg and the gEEProg manual here
Download my translation (from the original German) of the SDA-2006 datasheet here

Download the schematic, PCB layout, parts list, and source code for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files. Also, MPLABX (available from microchip.com) will be useful when opening the project file containing the source code.

MPS 6540 Commodore PET 2001 ROM Adapter (Obsolete Rev. 3 Version)

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I have been selling ROM adapters for the Commodore PET-2001 since 2009. Over these last five years I have been honing my design skills on my many different replacement electronic parts and through that process I have realized that my adapters are much in need of an update, so here it is. (If for some reason, you would like to buy the old version, it is still for sale here.) This new generation of ROM has many improvements including:

-A 74HCT138 decoder IC instead of the primitive diode-transistor logic used in the first version. This means a more reliable replacement that more accuratly mimics the original MPS6540.
-The clock signal is now wired as an additional ‘chip-select’ line to more closly mimic the behavior of the original MPS6540.
Batten and Allen PCB edge pins instead of round wire pins. The old adapters would only work reliably in one of the two types of DIP socket used in the original PET. These new pins exactly replicate the shape of a proper DIP pin and thus will work reliably in any DIP socket without damage. No kind of through-hole pin can claim this!
-An overall lighter weight and shorter design. This means that that part will be less likely to come loose from the socket if the PET is jarred.

You will receive:
– One adapter capable of replacing a single MOS Technologies MPS6540 ROM chip.
– The needed 2716 ROM chip, programmed with the code you need. Please specify the full part number of the original chip when ordering so that I can program the replacement correctly.
– A lifetime guarantee on the adapter. If the adapter does not work in your computer I will work with you until the problem is solved. If the adapter ever fails, just mail it back to me for a free repair.

PLEASE NOTE: These adapters will ONLY work to replace a chip with a part number starting with 6540. They will NOT replace types 2332, 2316, or other ROM types used in Commodore computers other than the original Commodore PET 2001. If you don’t know if you have a bad ROM chip, or if you don’t know which one is bad, you may be interested in my EPROM Programmer Universal Adapter which, when used in conjunction with an inexpensive Willem EPROM programmer, will allow you to read (and therefore test) an MPS6540 ROM chip. You can also read my guide to troubleshooting the Commodore PET 2001 here.

These adapters replace MOS Technologies proprietary ROM chips with standard 2716 ROM chips and have the following features. They:
1) Are pin-compatible electrical replacements for the mps6540 (except that they do not require a clock signal.) All five chip select lines are fully functional.
2) Have a small enough footprint that the adapters can replace any or all of the ROM chips in a PET 2001.
3) Use only vintage-style through-hole parts so they will not look out of place in a 1977 PET.

The one disadvantage of these adapters is that with a 2716 inserted they are about 0.3″ taller than the original 6540 chip and thus may not be mechanically compatible with all 3rd party expansion boards. Please make the appropriate measurements before ordering.

Download the schematic and PCB layout for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files.

Replacement Inguard ROM for the HP 3455A Voltmeter (HP P/N 1818-2270)

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Do you have an HP 3455A voltmeter with a bad inguard ROM? If so, this is the part you need. The inguard ROM chip in this popular meter is a 100% custom HP part, but with this adatper it is a simple matter of unsoldering the original and soldering in a replacement. Absolutely no other modifications to the instrument are required. If your 3455A happens to have the 1818-2270 in a socket, don’t worry – this part uses Batten and Allen PCB edge pins which exactly replicate the shape of DIP pins, assuring compatibility with all DIP sockets.

If you are not sure if your voltmeter has a bad ROM you can easily test the original ROM chips in your meter using my EPROM programmer universal adapter. For more information, please see the product here.

A more technical description of the ROM chips in the 3455A follows:

The outguard ROMS are pretty standard for the era – they are MOSTEK MK31000 which are equivalent to types 2316A, 8316A, AM9217, and prehaps others as well. This same pinout was used for a whole lot of 2k PROMS. One thing to note is that the CS lines are programmable on these and HP chose to make CS2 and CS3 (pins 13 and 14) active low but CS1 (pin 15) active high.

The inguard ROM (0.5kb) is much more interesting. It is a 100% custom HP part and besides an odd pinout it is unique in two ways. First it requires -2V and +15V supplies. It was not uncommon for early ROMS to require a high voltage supply as well as a negative supply (think 2708 or 2513), but these supplies were almost always +12V and -5V. The second odd thing, and this is really odd, is how it does chip select. In order for the device to be selected pin 12 has to be in the opposite state of pin 13, the highest address line. Put differently, ~CS = XNOR(pin 12, pin 13). My replacement uses a 74LS02 to implement an XOR gate and recreate the original chip select functionality.

Download the schematic and PCB layout for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files.

MPS 6550 Commodore PET 2001 RAM Adapter

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I have been selling adapters to replace the MPS-6540 ROMs in the Commodore PET-2001 since 2009, but until now, there has not been a solution for the equally scarce MPS-6550 RAM chips. This product finally solves this problem once and for all by making a simple way to replace a 6550 RAM chip with a common 2114 RAM chip! These adapters feature:

-Fully functional pin-compatible replacement for the MPS-6550.
Batten and Allen PCB edge pins. These pins exactly replicate the shape of a proper DIP pin and thus will work reliably in any DIP socket without damage. No kind of through-hole pin can claim this!
-A gold-plated machined DIP socket to hold the 2114 RAM
-A light weight and low-profile design that fits easily in the PET and is unlikely to come loose from the socket if the PET is jarred.
-All visible components are vintage-style through-hole parts so the adapter will not look out of place in a 1977 PET.

You will receive:
– One adapter capable of replacing a single MOS Technologies MPS6550 ROM chip.
– The needed 2114 RAM chip.
– A lifetime guarantee on the adapter. If the adapter does not work in your computer I will work with you until the problem is solved. If the adapter ever fails, just mail it back to me for a free repair.

PLEASE NOTE: These adapters will ONLY work to replace a chip with a part number starting with 6550. They will NOT replace RAM types used in Commodore computers other than the original Commodore PET 2001. If you don’t know if you have a bad RAM chip, or if you don’t know which one is bad, you should read my guide to troubleshooting the Commodore PET 2001 here.

The one disadvantage of these adapters is that they are about 0.3″ taller than the original 6550 chip and thus may not be mechanically compatible with all 3rd party expansion boards. Please make the appropriate measurements before ordering.

Download the schematic and PCB layout for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files.

PC AT PS/2 Power Supply Load Tester

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The PC / AT / PS2 Power Supply Load Tester (also known as the AT PS Test) is a compact and convenient device which allows for rapid testing of computer power supplies utilizing the connector pinout standard defined with the original IBM PC. This standard was used in the PC, the XT, the AT, some PS/2 systems, and most clones up until around 1995 when the ATX standard became the norm. Power supplies using this standard (and thus compatible with the AT PS Test) are easily identifiable since they utilize two six-pin connectors (usually labeled P8 and P9) placed side-by side to supply power to the motherboard. See the product images for an example of what these connectors look like.

Such supplies will typically not start unless a minimum load requirement is met (this can be quite high – up to ~50% of full load.) Thus, the AT PS Test contains on-board load resistors to provide this load to the supply under test. It also provides status LEDs which indicate the presence of sufficient voltage on each of the rails as well as the presence of the ‘Power Good’ signal from the supply.

In addition, the AT PS Test has banana plug biding posts for each supply rail and jumpers to disconnect the on-board load resistors, allowing it to serve as a break-out box for testing power supplies with an external electronic load.

Note that there are many power supply testers available for sale on eBay and elsewhere, but this is the only one (that I know of) which has the correct connectors for AT style power supplies and the only one which will provide sufficient load to turn one on. Newer (ATX) supplies need a much smaller load.

For a complete description of all the features of this handy device, please download and read the complete user and service manual at the link below.
AT PS Test User and Service Manual

Download the schematic, PCB layout, and parts list for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files.


MPS 6540 Commodore PET 2001 ROM Adapter

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I have been selling ROM adapters for the Commodore PET-2001 on eBay since 2009. These new Rev. 4 ROM adapters feature:
-Pin-compatibility with the obsolete MPS6540 ROM chips used in the Commodore PET 2001.
-Correct implementation of all five chip select lines on the MPS6540 using a 74HCT138 decoder IC. As with the original part, a low state on the clock pin will also deselect the chip.
Batten and Allen PCB edge pins which exactly replicate the shape of the original DIP pins and thus will work reliably in any DIP socket without damage. No kind of through-hole pin can claim this!
-Only vintage-style though-hole parts so they will not look out of place in a 1977 PET.
-A small footprint and light weight and short design so that the part is unlikely to come loose from the socket if the system is jarred.

You will receive:
– One adapter capable of replacing a single MOS Technologies MPS6540 ROM chip.
– The needed 2716 ROM chip, programmed with the code you need. Please specify the full part number of the original chip when ordering so that I can program the replacement correctly.
– A lifetime guarantee on the adapter. If the adapter does not work in your computer I will work with you until the problem is solved. If the adapter ever fails, just mail it back to me for a free repair.

PLEASE NOTE: These adapters will ONLY work to replace a chip with a part number starting with 6540. They will NOT replace types 2332, 2316, or other ROM types used in Commodore computers other than the original Commodore PET 2001. If you don’t know if you have a bad ROM chip, or if you don’t know which one is bad, you may be interested in my EPROM Programmer Universal Adapter which, when used in conjunction with an inexpensive Willem EPROM programmer, will allow you to read (and therefore test) an MPS6540 ROM chip. You can also read my guide to troubleshooting the Commodore PET 2001 here.

The adapter is about 0.3″ taller than the original 6540 chip and thus may not be mechanically compatible with all 3rd party expansion boards. Please make the appropriate measurements before ordering.

Download the schematic and PCB layout for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from expresspcb.com before you can view the files.

Useful resources:
2716 Datasheet
6540 Pinout
The product page for the original 2009 Rev. 1 version of the adapter is available here.
The product page for the 2013 Rev. 2 and Rev. 3 versions of the adapter is available here.

Skil 1614 and 1616 Chainsaw Fuel Filters

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Are you repairing a Skil 1614 or 1616 chainsaw? Is the original fuel filter disintegrated or clogged with old gas? If so, you need this special custom-made reproduction fuel filter. It replaces Skil P/N 180635, that has not been made for years.

Most chainsaws have a small weighted fuel filter that is free to fall to the bottom of the tank so that the saw will run in any orientation. However, the Skil saws use a large fuel filter made of a fine foam which soaks up gasoline like a sponge allowing the engine to be fed a continuous supply of fuel in any orientation. The tank is not shaped correctly to use a weighted filter and so you need to replace the old filter with a new one of the same design.

Installation is easy, but do note that the original plastic hose barb must be reused. For a discussion on fixing these saws and a cross-reference list of other parts you may need, please see my blog post here.

Black and Decker 73566 and 73074 Bench Grinder Clamp Washers

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These parts are replacements for the grinding wheel clamp washers used in the Black and Decker 7900 bench grinder. If you own one of these venerable old grinders but have lost or bent one of the clamp washers, these are the parts you need to get to get it going again.

As stated in the manual, you must NEVER use regular flat washers to clamp the wheels. Use of flat washers can cause the wheels to crack or even explode in use, potentially causing a serious accident.

These washers have been custom made on a CNC lathe out of carbon steel to the original Black and Decker dimensions for true-running wheels and long life. To reduce the risk of corrosion they are plated with zinc (outer clamp washer) or black oxide (inner clamp washer) just like the originals.

They were designed to fit the Black and Decker 7900 bench grinder, but may fit other models. Refer to the drawings below to determine if they will work in your grinder.

Drawing for Inner Clamp Washer – Black and Decker P/N 73074

Drawing for Outer Clamp Washer – Black and Decker P/N 73566

Manual for Black and Decker 7900 Bench Grinder

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