Are you sure they're 9902's? Those IC's are UART's and are generally used on the RS232 board. More likely the PALs are at fault. They're very sensitive to any spikes or surges since the card has no electrical buffering. I would also like to find someone who can burn new PALs. My REV A 9900 will need them. Last week someone on eBay was selling a new lot of 5 PAL12L6's for $22.00. Before I could get back to them someone snagged them. The PAL's aren't much good unless you can find someone who can read the code from a good one and then burn it onto a new one. Trying to get in touch with the CTIUG 'cause I'll bet someone in the group still has an eprommer. Problem with CorComp was they were never very forthcoming about details of their card. They could have released that info to the TI community when they went out of business. Would love to see a schematic of the 9900 card and/or the equations that were burned onto the PALs. It also might be possible to contact W.R. Moseid for some info. He was one of the CorComp team. Only other way I can think of is to borrow a couple from a good 9900 and copy them. Also hope some more come up on eBay
Yes, the power plugs into the 9900 Micro Expansion system (should have clarified that) through the RS232 portion and the system could be purchased as a RS232 only system, and the disk controller could be purchased and added later, if I understand correctly. This means that without the disk controller addon, which also houses the 32k memory portion, you still had 9902's (two of them), (1) 1489, (2) 1488, (1) 9901, (1) 74LS123, (1) PAL, (1) Eprom ( I believe a 27128 series), (1) 74LS2244, (1) 74LS04, the system should still boot. But all I get is the cyan screen. Now I haven't checked the resistors and caps as of yet, but I am still leaning to the PAL as the culprit, as I have checked and/or changed all the 74 series chips, and have swapped out the 9901, and removed the 9902's and each of the other chips and retested, no difference.. On a side note and as stated in the beginning of this thread, my Corcomp disk controller card can be used but only with the Geneve, and a member of this forum already sold me a replacement set of the Miller Graphic eproms, that would not even let the Geneve use the card. I had to go back to the old MG set. The PAL is what I was suspecting on this one too, and your words have strengthened that, though not conclusively.
Edited by RickyDean, Wed Jun 1, 2016 11:11 AM.