Help to locate the fault on X68000 ACE motherboard.

[SQZ]

Hi!

After some weeks of testing, finally I recognize that I need help with this. It is a faulty X68000 ACE I wanted to repair.

The symptoms are shown in the videos below:

- video 1 (at power-on): https://www.youtube.com/watch?v=5T0ZB-Q1WI4
- video 2 (pressing interrupt button at some point during power-on): https://www.youtube.com/watch?v=Xgwm1dJe54E

It seems to stop at some point in the machine boot process, as it doesen't reach to the "read floppy" stage. If you insert a floppy disk, led remain solid green all the time.

As I have other ACE (a working one), I could test one by one, the parts of the faulty one on the working one. I suspect that the problem is only with the motherboard.

Tests and conclusions done so far:

- I/O board: 100% working (tested on the working ACE)
- Both floppy drives: 100% working (tested on the working ACE). Cables also tested, 100% OK.
- Power Supply:  100% working (tested on the working ACE). Also tested with a new adapted ATX PSU. No changes.
- CPU: Replaced with new 68000. No change
- ROMs: Tested with known working EPROMS and jumper setting: No change.
- Riser expansion board: Reseated. No change
- Capacitors: Recapped motherboard: No change.
- SRAM: Reset. No change

Also I put the non-working ACE's motherboard in working ACE's case... no change, same symptoms. Must be something in the motherboard.

Impressions about the motherboard, after some visual inspection:

- OSCIAN chip seems to have been replaced (on the solder side of the board, you can see yellowed resin/flux-like on the pins.
- MESSIAH chip have almost all the letters over the chip deleted. you can barely read "SHAR..." and "..SSIA..".
- OHM chip have the same yellowish resin/flux-like solidified paste over the pins, all around the chip. Checked with a magnifier, it seems to have all the pins OK, no shorts, no broken traces...
- CYNTHIA and VICON seems to have some rust over it, in the metallic part, nothing serious. They both also seem to be socketed (originally, because the solder under it are perfect). I tried to reseat the, without changes in symptoms.


At this point I don't know what to test. I have tools and materials to test and repair (multimeter, low-cost lpt-port oscilloscope, cabling, soldering station, etc...), but I have no idea of what to check now.

Any help will be highly appreciated.

Thanks

[eidis]

 Hi SQZ !

Flux residue can eat up traces over time so the first thing to try would be a continuity test of the traces in repaired areas. The schematics can be found in the X68000 FAQ.

Keep the scene alive !
Eidis

[SQZ]

Hi,

Thanks. Continuity test done on all traces on both chips after cleaning resin/flux residue with special flux remover liquid. Traces are OK.

Anyhing else?

[eidis]

 Hi SQZ !

Next step is to switch it on and see if any of the chips, especially RAM chips are getting hot after some time. If all looks good, check the CPU reset line and read the following articles for more inspiration:

CPU Reset Lines
http://newlifegames.net/nlg/index.php?PHPSESSID=debedb4114ee9fe30cb7d81c84ef74d6&topic=19.0

Repairing Game Boards - Troubleshooting Steps (post #2)
http://newlifegames.net/nlg/index.php?PHPSESSID=debedb4114ee9fe30cb7d81c84ef74d6&topic=22.0

And I saved the best for last.

How to fix PCBs - A Beginners Guide
http://forums.arcade-museum.com/showthread.php?t=177192

Keep the scene alive !
Eidis

[spud]

Sorry to revive this old thread.

The schematics can be found in the X68000 FAQ.

Still haven't had the time to check my first ever X68000 (ACE HD). Everything has arrived in the mean time, voltage converter, new system disk, 1 game (Overtake), mouse & keyboard adapter. So I should be all ready to go.

The X68000 has recapped PSU and floppies, but I think not the PCBs. So I guess that's a job that still needs to be done sometime. I don't see any ACE (CZ-611C-GY) specific schematics in the FAQ. Are they identical to the original X68000 (CZ-600C) schematics that are in the FAQ?

[ShootTheCore]

No schematics are out there for the ACE that I'm aware of, but there is a capacitor list here:

https://gamesx.com/wiki/doku.php?id=x68000:x68000_ace_capacitor_list