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.
The PET 2001-8 Video Mixer Adapter arrived safely today. I am very pleased with it. I have 4 PET 2001-8 computers in my computer collection that I want to make work. ( view my collection at http://www.myoldcomputers.com ) I tried the PET Video Mixer Adapter on my oldest PET, a 1977 board with MOS 6550 RAM Chips installed. I connected the Video Mixer Adapter to a Commodore 1702 Monitor and it worked flawlessly. I used the troubleshooting methods described on your web site and found 2 bad chips at I1 and J3. The PET now boots to the Commodore BASIC screen with 6143 Bytes free having the I8 and J8 RAM sockets empty. I have a parts machine that has the MOS Chips so I am going to swap out some of the chips to replace them. Thank you very much for your adapter which made the troubleshooting process safer for my vintage PET computers and showing me how to fix my computers.