realpeterjack wrote:But it would run, at least, wouldn't it? That would let me know the video generator and processor are OK, at least.
The 8301 can generate a video image without a CPU. It would just be black because the CPU can't put any data in the RAM, but it would be a valid video signal.
realpeterjack wrote:I've just started reading other forum posts and found something about Minerva. Do I have to make any changes to the PCB to get it running?
The ROMs on the QL are quite like EPROMs, except the /OE signal is inverted. On one it is active high, on the other active low. So Minerva on an EPROM comes on a little carrier board with a 7400 or similar to invert the ROMOE signal.
realpeterjack wrote:Thank you for the offer. Right now my biggest concern is having no spare parts to check it for problems. I want to have it booting to the prompt, at least, then I may pursue fixing the drives (it had only one installed). I think trying to randomly replace RAM chips would be a waste of time and possibly good ICs, so I basically have two options:
I could ask the friend who gave me this QL to test the socketed ICs on his working QL;
I could get a Minerva rom and perform more testing on my own.
So, it safe to swap the possibly bad parts into the working QL?
It is safer to test the questionable components on the working QL than to take known good parts and risk them in a potentially harmful faulty QL. If you determine you have any faulty ICs, I have spares here I could include in the package.
realpeterjack wrote:I think I'll have to keep from investigating the problem any further until I get either the Minerva ROM replacement or authorisation to test my chips inside a working QL. Even if I replace all memory chips that would not ensure having it in full working order...
Well here's some things you can do...
Tie the data pin of each RAM IC to GND and see if/how that affects the output.
Check RASL, CASL and WEL are being generated and distributed properly.
Check the 74LS257s are being switched properly, and are functioning correctly.
Check X1 and X2 are both making 15 MHZ, and you see 7.5MHz on CLKCPU (8301 pin 7, CPU pin 34)
Reference clock pic: