Microelectronics | Siemens 80386DX ISA Single Board Computer

Synopsis

Honestly, I bought this board for spare parts. I originally wanted to extract the CPU and FPU sockets and also the cache controller for my experiments. It was fairly cheap and very corroded under the parallel port. Also, some traces of heavy corrosion were underneath the PCB, in the same area. So it was cheap. Very cheap, I would say. The parallel port connector was an old style Harting part with elongated pins. Since I had one of these in my spare parts box (extracted from my defunct Micro Z80 project), I decided to attempt to replace it.

Disclaimer
This article is not to be treated as a do-it-yourself tutorial on how to fix, restore, rebuild, or improve this unit. This was not my initial intention. But you can consider this whole content as a general guideline, should you decide to attempt any service procedure on an identical or similar unit.

The entire documentation is just a reflection of my work and I cannot be held responsible if you damage your unit, or even harm yourself in the process.

Repair

The operation was straightforward. I struggled a little bit with the rust on the PCB, but I cleaned it up in the end. A phosphoric acid based solution did miracles. But then I had to quickly clean with acetone. All this without touching the solder points. I applied these solutions only on the dirty soldermask.

I'm pretty happy with the results.

Pictures

Here are some pictures that I took during this operation.

As a curiosity, this PCB was factory repaired at some point. The job appears to be done by a skilled technician. But it still looks ugly. I've seen better digital PCB repair jobs. Now I'm thinking about using this single board computer somehow.

There is very little rust left on the PCB.

The new connector looks very old-school.

On the solder side there is almost no rust near the parallel port pins.

Overall, the PCB assembly is very crowded and packed with components.

Detailed view on the said repair job. This chipset appears to be an early one as there are a lot of logic ICs and PALs involved in the implementation.

Junk parts. The metal bracket can be cleaned to a certain extent. But since the chrome (or nickel) plating is cracked in multiple areas, rust will resurface.

For the moment, this ISA card will return in the drawer. But it's ready to be used for a nice retrocomputing project.