Sinclair ZX80 / ZX81 / Z88 Forums

Hi all I have a problem with my ZX Spectrum toastrack...

Till some time ago everything was working fine...Now each time i power up the machine I get a thick white/black bands pattern with black frame (seldom with a few green dots) and the system is stuck. The strange thing is, if I reset the machine from the pattern screen the Spectrum boots normally (esxdos checks to white screen Spectrum 1982 etc..) and i can enter Divide/DivMMC menu through button. The machine often boots correctly also if I quickly switch off and switch on the Spectrum (I have a power switch)... Without Divide/DivMMC inserted the Spectrum quickly shows the pattern all the same and boots into menu.

I'm using an original European PSU, but i tried also With a 48k UK PSU and a compatible one...Same story.... I deeply cleaned the back connector with IPA, and i tried to power on without the keyboard attached...More of the same.

I have no problem in games once i launch them with Divide/DIVMMC (graphical glitches etc..) I was able to launch both B. Alford's "Tape Tests" utility and diagnostic rom through this method -> https://www.youtube.com/watch?v=wiPi8fVeYN8 ...The lower RAM tests result PASSED as all the other tests (I have a SLAM ULAPlus installed)...

What's wrong with my toastrack? I'm only getting suggestions, if a repairment is needed I'm going to pass everything to my modder/repoman.

Hope I was able to explain myself in a comprehensible way.
Thanks for attention.
A.

Not sure. Horizontal bands are unusual.

As it works once you get it going, I would suggest that you try replacing capacitor C27. This is the capacitor that is part of the power on reset circuit.

Mark

Hi,

Did you ever get this resolved Opossum?
I'm seeing a similar issue with my toastrack, and could do with some pointers!

Cheers!

Are you experiencing the same symptoms? Or are yours different?

Mark

Similar/the same I would say..

powering on from 'cold', I usually get same horizontal black/white lines (with random coloured squares), then it can take a power reset (or two) before I get into the boot menu.

Powering on with an expansion card (in my case DivMMC Future, or Retroleum smartcard) it appears fine. Running diagnostics from the smartcard shows all appears good though.

So try this: use a switched socket or similar arrangement so that you can use one hand to turn your ZX Spectrum 128K on. But before turning it on, press and hold the reset button/switch. Then while holding the reset button/switch, turn it on. After two seconds, release the reset button/switch. Does this make any difference?

If yes, renew capacitor C27.

Mark

So doing this, i hold in reset button, switch on at mains. Screen is corrupted (as described previously), releasing reset switch resets to a normal (good) menu screen.

Thanks for the reply 1024MAK btw!

I did do a recap when I first got the machine (few months ago), but this issue was present before the recap also. I'll open the case tonight and have a look at the capacitor you mention anyway.

I've tested with a couple of diag carts also, they appeared to check out OK (well, from my novice POV anyway! ).

Cheers!

1024MAK wrote: ↑Fri Mar 06, 2020 9:14 pm Not sure. Horizontal bands are unusual.

Hehe unusual is good.
I would even say, its unuseful.

Sorry to add to a post that's older now..

I've been chasing an issue like this with a toastrack I have.

It would present as a garbled screen at startup. Checked the RAM and found 2 chips dead. IC10 and IC11 - replaced them and then the fun started..

From cold, it will start with the vertical lines - or it will get to the menu screen and if left for a few seconds, the machine will reset to 48k BASIC. I thought it may be a ROM issue (as it will boot to Brendans diag board fine from cold or hot - and also the V3 Retroleum smartcard diag and pass all tests).

If I reset it a few times, I'll get the menu and it functions fine from that point onwards. Loads all 128k games/demos and all is good.

If I switch it off for about 10 mins, the whole process will kick off again.

Ok, so I thought, i'll give it a recap. Did that - every capacitor. Changed the regulator for a 2A 78S05. Checked all the voltages, all great (5.02v, 12.01v etc..)

Still got the same issue.

So, thinking about it, it sounded to me like an issue with a cap maybe? Narrowed it down (by switching off when the machine was 'warmed' up and working, and discharged each cap one at a time), then powering up the machine. I found that if I discharged BOTH C111 and C112, the issue would present itself. No other caps on the board cause the issue. And it has to be BOTH caps. Doing one or the other doesn't cause the issue to manifest itself.

Anyone have any ideas why that would be the case? Those caps seem to be involved in the 1488 serial chip circuit.. Not sure why that would cause the issue I'm seeing. Maybe a faulty 1488 chip??

Any thoughts are welcome..

KbJ