Grundy NewBrain - Part 6 (Troubleshooting pause)
13Not closer to getting it working ... but the replacement DC/DC converters (TDK CD-1683N) for the VFD arrived from Germany today.
The original DC/DC converter (TDK CD-1867N) is the wrong type for the VFD (apparently), outputting too-high DC voltage. So there is a bodge on it with a zener diode and a resistor.
Managed to find the correct converters (original TDK ones! WOW!) from a fellow in Germany - only €3.32 each.
I am amazed because even the "drop-in replacement" converter boards (model E2598VF from Endicott Research Group/ERG) that were released in 2003 for the "obsolete" TDK part are no longer available (2009-ish).
I've also decided, sod it, I'll try to replace the 16 MM5290N-2 DRAM chips with a single 32KB SRAM chip, so I've removed the RAM board as a start. General idea seems to be to use !CAS for !CS and !RAS for latch clock - half the addresses go direct to the SRAM and the other half are latched. Or something.
Next part, I think, will be seeing if I can get the SRAM board working ...
Correct DC/DC converter boards (194 left as of July 2022):
https://www.shotech.de/en/cd-1683n.html
Press release for ERG's replacement E2598VF in 2003 ... which are now also obsolete:
https://www.electronicproducts.com/vfd-supply-replaces-discontinued-part/
Idea for switching from DRAM to SRAM:
http://sindik.at/data/vram/