exxos's Atari, Amiga & retro forum

Have you done a continuity test between the pins with a multimeter to catch any shorts?

Thanks. I am not sure what the expected values are. I tested from pin 1 to each other pin and got the following:
1 to 2-9: 41
1 to 10: 0.3
1 to 11: 0
1 to 12-18: 44.9
1 to 19: 10.3
1 to 20-27: 41
1 to 28: 44.8
1 to 29: 0
1 to 30: 0.3
1 to 31 and 32: 10.3
1 to 33: 0
1 to 34: 10.3
1 to 35-39: 0
1 to 40: 44.8
1 to 41-44: 44.9
1 to 45 and 46: 0
1 to 47: 45
1 to 48: 0
1 to 49 and 50: 48
1 to 51-57: 41
1 to 58: 0.3
1 to 59-64: 41.2
1 to 65-72: 0
Does that help at all? Thanks.

It's more testing adjacent pins in case there's a solder bridge.

There is continuity between many consecutive pins in the SIMM socket: 3-4, 5-6, 7-8, 9-10, 12-13, 13-14, 14-15, 15-16, 16-17, 18-19, 19-20, 21-22, 23-24, 25-26, 27-28, 28-29, 29-30, 30-31, 31-32, 33-34, 34-35, 40-41, 41-42, 42-43, 43-44, ...

Not sure what is going on.

I think you should look at the H5 schematic and trace back the simm to the MMU. Looks like bit 8 may not be connected back the the MMU.

Thanks for your help. I will take a look at the schematics as you recommended.

I am sorry. I do not understand how to trace back bit 8 from the SIMM to the MMU.

Is it MDATA8 in the SIMM?

I see that DRD8 maps to D8 on the IC18. Is that correct?

However, the MMU only has D0 to D7. How do I trace DRD8 to D0-D7?

Thanks.

Sorry meant CPU not MMU.

MADx lines , check they go back to the MMU (via 33R resistors).

Connection of D8 goes from simm via the buffers as highlighted below.

Hmm. There is no continuity from pin 31 of the SIMM to pin 63 of the MMU (MAD8).

Later boards go through a jumper...