It’s been a while, but there was a lot of progress.
All the boards have now been built.
The powersupply board works as should. There was an issue with the voltage regulator being not strong enough (1.5A), so it’s been replaced with a 2A variant and now it works nicely. It gets hot though. The mainboard draws quite a bit of energy. Per suggestion of PaulMc, I’ll b trying to replace as much of the 74LS ttl to 74HTC variants and see if that will lessen the load a bit.
Regarding the mainboard, things are a bit complex. It seems to work…shortly. It boots but then hangs in either of the following three screens. Uusually it halts on “Memory is write protected”, with the buzzer continously beeping. Sometimes it halts on either of the other screens.
Probing around with the scope shows that the CPU actually remains active and the CPU’s MREQ is continiously probing, so at this point it needs some hardcore debugging, which is a bit of a learning curve. One thing Paul is worried about is crosstalk on the PCB and I’m going to try run this thing on a 2Mhz crystal and see if that makes a difference.
To be continued, but here were are at the hard parts 🙂
I’m amazed at how wel Paul managed to turn these schematics into actual PCB’s!