Sinclair ql black screen

[Popopo]

Just checked IC21 on the A side I am getting this.
https://youtube.com/shorts/Jo_yYMqE690? ... wfYpTOwIbr
And on the B side I am getting this
https://youtube.com/shorts/1tZc5g3p2wQ? ... Wu6W-mENJz

On Side B this happen to each line?

So, everything that works on side A (CPU, etc) works.
Now we can focus on side B, mainly RAM IC, ZX8301/2 and of course, this IC21 (very low low probability of faulty one, but keep it in the list if the rest fail).

What about the test of heat? did you lay your hand on the RAM ICs to check if there was one hotter than others?

Do you have hot air gun?
Do you have soldering skills? (I guess yes)
Do you have RAMs 4164 or similar spare?
IF so and you have one RAM working IC spare (could be from another computer) and since YOU HAVE NOT SHORTS between +5V and GND nor between +5v any DATA NOR ADDR Line on the RAM ICs, you could place it on piggyback on each RAM IC (WITH MINERVA placed) .

That may work and give you a nice booting screen IN CASE of only 1 RAM IC faulty. In case of more RAM faulty IC, with Minerva place you could detect the second one. The probably increased a lot. So please to use Minerva ROM instead original. Just check that pins of Minerva ROM may good contact with socket, and the socket has not cuts on the PCB. That is something interesting to check, on the bottom of the PCB if there you see suspected track cuts or bad soldering joints.

In case we are lucky, you will find out the faulty RAM IC, in case not, we could focus on ZX8301 & ZX8302 (without forgetting the RAM ICs yet).

[Traindriver69]

Hi
It's funny I am in the process of trying the ram with minerva now
I am getting this screen which looks like it is trying to give a ram error but can't.

[chriskgnr]

Maybe the address decoding ic's?

[Pr0f]

I remember seeing output like that with Aurora card and qubide where my qubide card had a bridge between 2 address lines, causing a short on the bus. The regular repeating black lines are a giveaway. I would check the adjacent address lines and see if you have a solder bridge somewhere, could be a speck, a component lead - it may not be big. A multimeter on continuity check when the QL is powered off will be useful to check address lines - if you've resoldered any sockets / chips - check them first.

[Traindriver69]

I have not done any work on it as yet and when I got it all the warranty stickers were intact.

[Popopo]

Nice step forward.

Please, write down what you have done of advises or what not yet. In order to know how is going on the real state.
Otherwise we are not synchronized.

[Traindriver69]

I have tried the heat test on the ram none getting hot and found one spare 4164 ram chip I have I tried piggybacking each ram chip but made no difference.

[stephen_usher]

Can you burn an EPROM? If so put my diag ROM (see separate thread) on one and use the Minerva ROM adapter with it. You should get some useful information about which RAM chip(s) may be an issue, or if everything's bad, one of the support chips.

[Traindriver69]

I do have a eprom programmer but the minerva rom is soldered direct to its adapter board so rather then damaging it trying to swap roms I would have to buy the bits.

[Popopo]

Hi
Sorry for answering late. Too many task to attend.

The test in piggyback is not a final word you may have more than 1, or (even if you didn't detect it ) one of those RAM IC has shorts between ADDR lines.

The Stephen ROM is a good way but I understand you pretty well about cannot reprogram the EEPROM on this Minerva EEPROM Adapter.

I didn't read the answer to:
3rd. Have you re-seat the socked ICs and cleaned their sockets with alcohol iso.propyl or any contact cleaner yet?

Perhaps to unite all what you have done in the first message of your thread, would unite all what you have done and make easier to continue.

Next week I will take out my QL with oscilloscope and study the scheme again to aids you a little better

By the way, From where are you from? in case somebody nearby you could bring you local aid.