Still no shipping info on the RGB2HDMI. Found some ram at a price I was willing to pay, but the earliest it’s supposed to arrive is October 30. If the ram turns up early, then I may take another look at the SCSI/RAM expansion card, though I’m not gonna get my hopes up.
Took the SPAL and ZPAL out of Disk Controller with the V2.2 ROM and ripped them. Decided to have a look at the RAM/SCSI Expansion PALs and noticed that apart from one 16R8, five of them are 20L8’s, and one is a 20R8. The ChipTester didn’t support 20L8/R8/R6/R4s PALs with the firmware I had on it (v3.4.2, latest at the time), but I put in a request with Evie at BackBit.io and in less than 24 hrs these were added to the latest firmware (v3.4.3), since they’re essentially the same idea as the 16L8/R8/R6/R4s just with more pins. The newer firmware logs details about L series PALs as well (which pins are mapped as inputs/outputs), so I’ve gone back and re-ripped all the PALs to collect all this info, beyond just the binary data.
FWIW: I really can’t overstate how satisfied I am with the BackBit.io ChipTester V2. It’s been a rock solid device and the support Evie provides is just amazing.
Also removed all the chips from that same Disk Controller in preparation for soldering/clean-up. I tend to leave chips in boards where possible unless I’m in the middle of something that requires their removal, as it’s too easy to accidentally bend a pin. This board was the one with the SCSI hardware/socket populated, but with a dead Z80. Time to solder up all the vias, then give it a clean and then check/touch up any joints that look in any way sub par, same as I did with the motherboard.
Bottom of board before soldering up all the vias/unused pads:
When I did all the vias, I also:
- Fixed up the alignment on the molex connectors that power the floppies.
– May replace these later. There’s 2 different types of connector here. - Realigned the 16 Mhz oscillator crystal, as it was sitting at an angle.
- Installed M2 metal screws to hold the IDC sockets for floppy/SCSI onto the board.
- Installed M3 nylon screws into the remaining blank holes that are for brackets and connectors.
Filling all the big holes with screws means less cleaner gets on the component side.
I also installed headers SJA-0 and SJA-1 for the Channel A onboard serial port. The serial ports hang off a Zilog Z8530 SCC connected direct to the Z80, allowing the Z80 itself to run serial operations, completely separate to the MC68000. It’s also apparently possible to use this for debugging the board. While I don’t have a spare Z8530 at the moment, populating the headers for Channel A at least is a no-brainer.
Of note: There are 2 sets of headers per serial port, on this board and also on the motherboard, all with the same pinout. For Channel A, they are SJA-0 and SJA-1. The SJ*-0 header is RS232 level and allows you to rewire the outputs to specific pins, including putting +12 and -12V power on specific serial pins. The SJ*-1 is TTL level and allows you to rewire specific outputs from the Z8530 to the RS232 level shifter IC’s (MC1488/MC1489’s). This means you can do things like loop back at the TTL level or the RS232 level just with jumpers, bypass a faulty input/output gate on one of the RS232 level shifters (if you have one unused), or tap off RS232/TTL serial from these connectors for all sorts of uses eg: directly to other devices, implement different serial types like RS422/423, have connectors located elsewhere on the case, etc.
Top of board after soldering up all the vias/holes, but before cleaning:
Once again, cleaned the board with Servisol Circuit Board Cleaner NA-1008.
Bottom of board after cleaning, prior to fixing joints:
Close up pic of some of the joints (around the Z80 socket):
Things to do next:
- Now that I can actually see all the existing joints, time to fix them all up.
- Perform a raft of continuity tests around the Z80 and compare to the other Disk Controller board, where the Z80 was fine.
– Definitely don’t want to plug my remaining Z80 into this board and kill it. - Go through the some of the comissioning tests (hopefully).