This project consists on an minimalistic expansion card with 3 ISA slots for the Amstrad PPC512 and Amstrad PPC640 "portable" computers from 1988. These computers are based on the NEC V30 (8086 compatible) with either 512KB or 640KB of RAM respectively and they expose all the signals of the standard ISA slots on two D-sub connectors on their backs.
I started working on this project back in 2016 but it has been dormant until January 22, 2021. On this day I noticed a Youtube video by Noel Llopis regarding PPC512 upgrades [1] and that triggered something in me to get this project finished.
Following the instructions on the Amstrad PPC technical/reference manual:
Contrary to the instructions of the reference manual, I decided not to power the PPC using the expansion ports and do the opposite: let the PPC power the expansion card.
Since I will only be using low power cards like a XT-CF card to add a "hard disk" and maybe a VGA card (which I still have to find), they will be powered by the PPC, ie, parasitically.
Not many parts are required to make this expansion card.
| ID | Part |
| X1 | 25 pin D-Sub male for cable |
| X2 | 37 pin D-Sub male for cable |
| C1, C2 | 100nF/50V 0.1" capacitor |
| C3, C4, C5, C6, C7, C8 | 10uF/25V capacitor |
| IC1, IC2 | 74HC244 + DIP20 socket |
| RN1 | SIL 10K * 8 resistor pack |
| X3, X4, X5 | 62 pin ISA socket |
| H1, H2, H3, H4 | Mouting holes. I'm using 30mm long screws and nuts to support the weight of the expansion card plus other ISA cards |
The PCB is pretty straightforward. Both D-sub connectors are soldered directly to the PCB edge and the PCB itself should be supported by four screws set to the height required to level the PCB and also mechanically support the expansion cards. The cards should have their ICs facing the PPC with their metalic blades to the right side, when looking to the computer from the user perspective.
Here's a view of the expansion D-sub connectors on the back of the computer, right beside the power input jack.
It took a while to get the prototypes but once they arrived, I quickly assembled one, well partially assembled it with the minimum number of parts, and connected it to the PPC.
It didn't work properly the first time I tested it because I made a mistake in the schematic. The PCB also has that same mistake but the fix consists in cutting a trace. See if you can spot it on the next pictures. More details at the end of this page.
This is the first version of the PPC expansion card I built and, as it happens so frequently with first releases, I found a problem when assembling it. I accidentally left pin 20 of the expansion connector B connected to the +12V line and that causes the computer not to start.
This line is used to disable the internal switching power supply of the PPC when it is being powered by an expansion card. This was my original idea and is also what the service manual tells us to do. But since that does cause the PPC to become unstable I decided to not power the PPC from the expansion card but go the other way around and have the PPC power the expansion card.
So, unfortunately pin B20 was incorrectly left connected to +12V and this prevents the computer from starting.
To fix it, the trace coming out of pin B20 (pointed by the arrow on the picture below) has to be cut. After doing this the PPC will have no problems starting up and the expansion card will work properly.
This will be addressed in a newer version of the card.
Published on Thursday 2021/01/28, last modified on Tuesday 2021/06/08
