Luis' Build

[lrodriguezrullan]

I double-checked and there actually is continuity from pin 31 of the SIMM to pin 63 of the MMU. I had to adjust the multimeter.

[lrodriguezrullan]

There is also continuity from pin 49 of the SIMM (DRD8) to pin 61 of the CPU (D8).

[exxos]

There is also continuity from pin 49 of the SIMM (DRD8) to pin 61 of the CPU (D8).

That cannot be right because the signal goes via the buffers...


viewtopic.php?p=90359#p90359


I would check another like DRD7 and see if the same happens.

[lrodriguezrullan]

OK. I double-checked and there was continuity between pin 49 of the SIMM and pin 61 of the CPU. I did not actually test on the CPU, but on the 5V Bus IO Port #1. Is that OK?

I also tested between pin 27 of the SIMM and pin 62 of the 5V Bus IO Port #1 and there was continuity too.

[exxos]

Any 5v port is fine.

I measured pin 64 and just ran my probe down the simm socket and there is no continuity. Not on pin 61 either. That is normal because the buffers are breaking the connection to the simm.

How are you doing continuity test ? I'm using multimeter just on ohms setting. I also assume you doing this with the power off ?

[lrodriguezrullan]

Correct. I wonder what could cause that.

[exxos]

I'm afraid I don't understand what's going on. If you have 2 problem data lines shorted directly to the CPU somehow, then you wouldn't just get 1 bit error on ram test. It doesn't make sense.

What do all the other 14 bits test as ? What ohms value are you reading ?

[lrodriguezrullan]

I am testing with my multimeter in 200 K ohms.
I tested the following and got 44.6 to 44.7 for all:

SIMM 4 and CPU 4 (D1)
SIMM 6 and CPU 3 (D2)
SIMM 8 and CPU 2 (D3)
SIMM 20 and CPU 1 (D4)
SIMM 22 and CPU 64 (D5)
SIMM 24 and CPU 63 (D6)
SIMM 51 and CPU 60 (D9)
SIMM 53 and CPU 59 (D10)
SIMM 55 and CPU 58 (D11)
SIMM 57 and CPU 57 (D12)
SIMM 61 and CPU 56 (D13)
SIMM 63 and CPU 55 (D14)
SIMM 65 and CPU 54 (D15)

Thanks!

[lrodriguezrullan]

I see what the issue is. I need to use a lower setting in the multimeter. I changed it to 20 Ohm and got no continuity for all the combinations between the SIMM and the CPU. Still need to figure out what the issue with the memory is.

[exxos]

OK so continuity is basically zero ohms. Or below 10 ohms for example.

I would resolder the simm socket and try diagnostic cartridge again. I'm also assuming you get the same bit error every time ?

While running diagnostic, just press down on various places on the motherboard and see if the bit error changes.