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.