PCjr. Power Supply Upgrades
Power is a necessity for computers, but power itself isn't very interesting to most people, it is what is done with that power that counts. Nonetheless, the computer still needs a clean and adequate supply of power to perform the functions and power the devices in it and attached to it that need it. The IBM PCjr. originally came with a rather anemic 33W power supply, then followed by a 45W power supply. The power supply came in two components, the first a large external transformer with long cables and second an AC-to-DC converter board inside the computer. The transformer uses electricity when the computer is turned off, has a rather proprietary connector to the card, can give off an audible hum and the constant usage will wear out the transformer over time as a result. The original IBM boards give off a lot of heat inside the machine and even the 45W card struggles to power more than three sidecar expansions.
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| Courtesy of Akbuku.com |
The picoPSU comes in a kit form for $15 which requires soldering and a fully assembled version for $20 and has a switch assembly similar to the original PCjr's on/off switch. The picoPSU retails for $25 and the external AC-DC power converter costs $16. You can pre-order an ATX2PCjr Adapter from here :
https://akbkuku.com/store/p/1/IBM-PCjr-ATX-Power-Supply-Adapter/
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| Courtesy of Retrotronics.org |
The second replacement power solution is the jrPSU from Retrotronics.org. This solution is a custom board with a full AC-DC power supply on it which replaces the original internal IBM power board. This card was designed by the designer of the jrIDE, Alan Hightower (alanh on the PCjr. forum). It does not need any type of external power brick, only a standard two-prong AC cable. It can output 5A at +5v, +12v and -12v. The pins are gold coated, I don't believe the original IBM cards used gold. Note the two-pin receptacle for the grounding pins on the PCB to the lower left of the big AC/DC module. The switch is a rocker like the original, but it is smaller and black where the original switch is red. More information is available here : https://www.retrotronics.org/home-page/jrpsu/
Currently, the design has exposed solder that go straight to the wall socket and can result in a user being shocked if they touch these points while the power supply is plugged in. Alan is currently designing a 3-D printed bracket to cover those points before he sells to the general public. He graciously donated one to me and I can't see myself going back to the IBM solution. This solution takes up a lot less space than the 45W adapter I have and a lot less heat. The only thing of concern I noted is that the power cord appears hard to plug in all the way into the outlet provided on the card, but you should not have to give it much force for a snug fit. The bill of materials cost for one of these is about $51.00, the AC/DC converter box alone costs $16.58
Both replacement power supplies cut themselves off from the wall power when not in use, which helps save on the electricity bill. Both projects are also open source, so you can conceivably make your own and save a bit.
TexElec Adapter Boards
TexElec has made something of a name for itself in the vintage computer community by making upgrades available from places that have had difficulty keeping them in stock like Lotech.uk. It offers two upgrades for the PCjr, both of which attach to the Expansion Ports at the rear of the system.
The first is the IBM PCjr. CGA and Serial Breakout Board. The second is the IBM PCjr. Joystick and Keyboard Breakout Board. I purchased the second, so I can speak to both products.
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| Courtesy of TexElec.com |
With the CGA and Serial Breakout Board, you can connect standard CGA monitors and Serial mice, modems and other serial devices. There are jumpers on the Board to select between positive and negative horizontal and vertical synchronization pulses. The default for most CGA monitors is positive sync. Unfortunately, using this Board means you cannot use either the PC Compact Printer or the PCjr. Display unless you obtain adapters for them. Moreover, the PCjr. Display accepts audio input through its video cable, but the D-shell connector has no pins for that, so you will need to tap the audio from the RCA jack and build a custom adapter to feed it into the PCjr. Display's cable.
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The best feature about the IBM PCjr. Joystick and Keyboard Breakout Board is the inclusion of a PS/2 keyboard port. This allows you to use a standard PC keyboard with the PCjr. The IBM PCjr. keyboards are awful devices to type on. The key layout is cramped, the keyboards are very lightweight and the keys use a rubber dome mat. There is an RJ-11 jack if you wish to use the original keyboard, but you will need a 4-conductor telephone cable (RJ-14) and it has to be a short cable. I was able to use my PCjr. with my IBM Model M keyboard with pleasurable results. One thing to note is that if you have a Model M with a detachable cable, don't use the extended-length cable. The regular length coiled cable works. Remember to set the jumper appropriately. You can hotplug the PCjr. keyboard but not a PC keyboard.
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| PCjr. Keyboard Diagnostic - PCjr. Keyboard |
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| PCjr. Keyboard Diagnostic - Model F/M Keyboard with Converter |
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| PCjr. Keyboard Introduction Program - PCjr. Keyboard or Model F/M Keyboard with Converter |
Lastly, if you use the IBM PCjr. CGA and Serial Breakout Board, the Cassette Port will be blocked by the Board and will be unusable. IBM PCjr. Joystick and Keyboard Breakout Board will block the Light Pen Port, the TV/RF Modulator Port and the Spare "L" Port, so you cannot use devices which attach to those ports. Still I do recommend their Boards and you can buy them for $28.04 for the Joystick and Keyboard Board and $19.54 for the CGA and Serial Board at https://texelec.com/
What Else Does a PCjr Need?
So between the upgrades and modes detailed in this post and in the last post, what else might a PCjr need? Well, for one a prebuilt and readily available and switchable solution for a PC-Sprint accelerator for one would be nice! A Gotek Floppy emulator should help with getting disks working, especially if you can't find a jrIDE. On the PCjr. forums you can find a disk image which includes images of all cartridge games and allows them to run off floppy. If you want to make a reproduction of a particular cartridge, the necessary files are available here : https://hackaday.io/project/19160-pcjrcart
I would like to offer two observations on the jrIDE as I have used it over the years. First, I have tried more than one DOM over the years and they simply do not work reliably in my experience. These days I use a 256MB SanDisk CF card and one of these CF-to-IDE adapters : https://www.amazon.com/Syba-SD-CF-IDE-Connects-3-5-Inch-Interface/dp/B000YUMLPI
This adapter is ideal because it provides power to the CF card without a wire. The CF card has never given me a problem and boots up reliably.
The second observation is that I have found that my jrIDE does not show the disk drive reliably if it is enclosed in a sidecar case. For whatever reason, whenever I use my PCjr. after an extended period, I have to readjust it in the slot to get it to show the "hard drives". The extra memory provided by the is detected just fine regardless of whether the drives are recognized. I find that letting the card sit "naked" on the end of the sidecars seems to be the best solution. It also allows me to remove the card to load more software onto it with my main PC instead of having to set up an Ethernet connection.
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