Issues with several KA640 CPU Boards

[spiceminer]

Dear all,

I am currently trying to restore a Microvax 3400 (KA640 CPU).

During startup, I get a few error messages, followed by "normal operation not possible".

The CPU is a "new one" recently bought from Ebay.

Apart from the CPU, two DSSI Drives (RF71 & RF73) are installed in the system and 2x 16MB Boards.







The errors are present with and without DSSI connected, with and without terminated DSSI connector at the enclosure (see picture above).
The presence of additional memory will not change the error msg. "SHOW MEMORY" does not indicate faulty pages.

The KA640 will not boot from DSSI and will not recognize the drives.



@Schroeder pointed me to https://www.pdp-11.nl/vaxsystems/mVAX3300/mVAX3300-info.html where a similar error message is reported.

Maybe this is no fault at all but indication of a false configuration?

The same enclosure but with KA650 & KFQSA & DELQA is working flawlessly including the DSSI subsystem.

I have another KA640 CPU which worked fine a few weeks ago:

including DSSI and network but it stopped working.
I get now no messages on the terminal at all and the LED indicator on the CPU panel is constantly showing an "F" - Initial State - no code executed.....
Eproms have been checked and ok...

Any ideas how I might move forward?

Thanks a lot
Stephan

 

[Schroeder]

I get now no messages on the terminal at all and the LED indicator on the CPU panel is constantly showing an "F" - Initial State - no code executed.....
Eproms have been checked and ok...

The CPU Board is on my table now. I did another visual inspection of the cleaned area of the board which was mainly impacted by a battery leakage. I soldered some parts even knowing that they had good contact just to be safe in case there is maybe a small cut which only disconnects when the board is inserted into the QBus. But with no success.

Obvious is the DC OK, green LED, remains dark. The reason for the board not starting. The signal DC OK is present on the QBus connector. Now, of course I need to understand what the board needs beside DC OK from QBus to function.
The board itself is no more complex than any of the boards from that area but schematics are difficult to find. My hope was on the VAX 3100 schematics but those are a really bad scan.

Does anyone has any schematics from a 3100 or QBus CPU card or an idea how these kind of boards deal with DC OK?

 

[wa2flq]

Check the power supply voltages. DC OK - off is a symptom that either +5v or +12v are out of tolerance. Electrolytic capacitor failures are common in equipment of this age. Processors won't attempt to start until this is corrected and DC OK is asserted.

 

[Schroeder]

The BA Box the CPU is sitting in is my test setup. Other CPU boards does work. Voltages are ok, DC OK and PO OK is present.
The Board did work before is was cleaned from acid. I have checked the cleaned area and traces are looking ok. Without schematics I will be lost ...

 

[cruff]

You should also check for bad solder joints, a microscope or magnifier (or magnifying camera) might be necessary. It may be possible when you cleaned it a bad joint opened up.

 

[spiceminer]

Does maybe anybody has such a CPU in user and can state if the "error messages" from the first posting point to a configuration error or an hardware issue?