The Sinclair QL Forum

Recently, I recovered a QL. A few days later, it started crashing at startup, and now it doesn't work at all.

The symptoms are as follows: when I connect the power supply, the video pattern appears on the screen, but unfortunately, it never completes. At the end of the random pattern, a white strip appears at the top of the screen, while the rest of the display remains in a random pattern. And that’s it—no further response.

It doesn't respond to the reset button. Occasionally, it reaches the F1/F2 screen, but the keyboard doesn't register any input, and it still doesn’t respond to reset.

Before replacing any ICs, I’d like to confirm where the fault is. Unfortunately, I currently only have a multimeter and a 200kHz oscilloscope.

Does anyone have any suggestions or ideas?

Thanks in advance!

Start by re-seating all ic's , and verify if the 68 is warming up .

be very carefull when lifting them !!

Which Rom are you using? I think my first thought is ZX8302 that would cause all those issues.

Thanks! My QL has a JM ROM and it's an Issue 6 board. I’ll try replacing the 8302—fortunately, I have a spare one.

I suspect there may be a bus-related issue. The last time I powered it on, after the random pattern appeared, it made some unusual noises and displayed a vertical pattern before crashing. Also, the microdrives activate randomly during startup, which doesn’t seem normal.

I think the 8301 is working, since the graphics appear to be generated correctly—VSync, HSync, and all video signals are present.

I’ve replaced both the 8302 and the 8049. There's been a slight improvement—now it occasionally manages to boot, and sometimes even responds to the reset button.

However, after a few seconds (no more than 5), the system starts to degrade and eventually crashes, showing random values in memory (and video, of course) and becoming unresponsive again.

I'm wondering if you have an unstable voltage - is this machine still running with the 5v regulator? If it is, you could try replacing that - they are not soldered (usually) so it's a just a matter of opening the case, removing the screw that holds the regulator to the heatsink - and then do your replacement.