Thanks to Tim, I received a rather special Geneve 9640. The board is non-working, dammaged and some IC are missing. It's a fun challenge for me to revive this great computer. This repair is above all a relaxed game, there's no hurry. And a lack of free time will lower the repair progress.
Here is the board received:
06/27/2018: I begin by a state of play of the missing parts:
VDP V9938
RTC MM58274
Audio SN76496
SRAM M5M5256P-15
Logic 74LS04
Logic 74LS244 X3
Logic 74LS245
Transistor 2N4126 X2
Crystal 32.768 KHz
Battery CR2032
LED
The first repairs:
- PCB deeply cleaned
- Thermal paste replaced for each voltage regulators (LM7805 and LM7812).
- Bottom side of the board: Many pins were bent/crushed to 90° and made short-circuits to the neighbours pins. I have straightened all of them.
- Damaged Solders on some pins crushed: Repaired
- Bottom side of the board: All excessive length of pins cut
- Capacitor C200 damaged : Replaced
- Crystal 12MHZ : One leg was broken: Replaced
- A crystal trace to C82 was broken: Repaired
- 74LS04, 74LS244 X3, 74LS245 installed
- CR2032 Battery holder soldered
- VDP 64 pins support badly soldered: Repaired
- 32.768KHz crystal installed
- LED installed
- Transistor 2N3906 Q11 & Q12 Installed (in replacement for 2N4126)
* Transistor Q200 (2N4401) dead: replaced
- 22uf 35V capacitors X7 replaced.
- 10uf 16V C12 Capacitor replaced.
- Broken trace already repaired with a long running strap. It's not secure, so a better repair made.
07/03/2018: It's time to power up the motherboard... No firework, no IC put into orbit. That is one point! But no video signal, I get a blank screen. Many work remain to revive the board.
- 18pin IC support installed on U203, replaced with a 14pin IC support.
- All the MB81256 IC replaced with KM41256-12
- Broken trace found under the EPROM IC support: Repaired. A former owner used a metallic tool to extract and made a scratch on PCB, cutting a trace
- Bad PAL IC - Replaced.
09/03/2018: The Gevene is working fine! I'm happy to have resurrected this board :)
Note about the Q11 & Q12 transistors:
When we look at the schematics of the Geneve9640, we see that all the two transistors are inverted according to the MM58274 datasheet (see Typical connection). A strange situation that it's interesting to study.
In the same time, I will verify all the schematics of the Geneve9640, to see if them contain eventual errors. It remembers me the schematics of the 99/4A that contains errors that I had to find all before developing my TIny-99/4A computers.
For this moment, and to repair quickly the Geneve 9640, I prefer to use jointly the two documents that show the 4 layers of the PCB. It's very interesting to study wher all the traces go.
