hmb's latest activity

As you pointed out for the Memory Merchant 65K16S board, the S100 address signals A0-A15 are latched by 74LS375s. The 74LS375 is a...

Correct. R1 is 270 ohms on both RevC and RevD boards. There is a typo in post 340 - the reference to "R1 should be 30K" should have...

I found an older (1980) version of the Cromix manual which only describes use of the 64KZ and no other RAM boards - which matches your...

I just quoted what the Z80 Cromix Admin Manual said. Perhaps it was a later version published after the original 64KZ had been...

The 256MSU and 512MSU boards are very rare, and either of them needs to be paired with the MCU board that performs the actual error...

It's complicated. The 64KZ RAM board instruction manual provides a very detailed description of several scenarios under which a Cromemco...

I expect you should be able to accomplish the same things a front panel does, with use of most ROM-based system monitors.

According to the schematic, test point "V" should be connected to pin 3 of IC14 - it will be inverted from pins 1 and 2 of IC14. You...

You may just have a poor signal feeding your scope when attached to test point "V". What do you see with the probe on either of pins 1...

The Dazzler "1976 Rev C" manual has a very detailed diagnostic/troubleshooting section...

Upgrading RAM on the original Z-120 main board involves more than just replacing the 64K RAM chips with 256K RAM chips. A kit containing...

Those RevD scans are very good!

Yes - the Rev D manual copy I have, with the illegible schematic, is from the Cromemco repository.

Unfortunately the schematic in the scanned copy of the Rev D manual that I have is almost illegible - the small section I reproduced...

This was mentioned earlier in this discussion - the Rev D board (vs the Rev C board that has been reproduced) included a couple of...