And the last two pics...
So, as I was saying when the unit boots up it does the RAM test, then it goes into "HARDWARE TESTING", then waits a few seconds, a beep goes on, and there it stays for ever...
The unit has 2 CPUs, one for the front panel and display and the other is the main control CPU. At first I though that one of them was frozen but it gets even more interesting to
test that both are working and responsive!
The front panel CPU has a test pin (17), that when pulled down displays test characters on-screen:
Hmm, there is activity in the main CPU too, and it seems that something is withholding the unit to continue its normal operation. Indeed, there is a watchdog timer
that generates and interrupt when it is not being taken care of properly, and this is the case after the unit starts beeping, an IRQ is generated and it is not attended:
Moreover and to my surprise, during all this time the crossguard controller of the A5 main CPU is still receiving and transmitting data (commanded by the MC68000 CPU) over the fiber optics in to the isolator board:
At this point one may be tempted to think that the CPU has gone into some kind of wild uncontrollable loop, but no
.
I decided to create a fault by removing the transmitter fiber optic that connects the outguard power supply A6 and the A/D converter and logic assembly. What the A5 CPU does puzzles me,
it turns off the beeper (on at all times up to now) and displays "ISOLATOR FAILURE" which is actually what it should do.
So to recap.
-NVRAMs passes the test, so the data buses and address lines are fine, at least address lines A1..A16 which are the ones needed to access those memories
-Both CPUs at A5 and A6 are working and responsive
-Timer seems ok
-Crossguard controller seems ok
-Front panel controller seems ok
I will continue the tests as time permits. Any idea or suggestion will be appreciated