Power-on issue, but reset is fine.

[Chr$]

I wondered if anyone has any suggestions to help me resolve this issue:

Issue 6 QL. When power is plugged in or when the wall power switch to the PSU is turned on, it never boots properly. Sometimes it just shows a black screen, sometimes coloured garbage, sometimes mdv1_ spins up accompanied by a coloured screen. Sometimes it shows the Minerva logo bottom right then goes black - it's all very random but never ever works from a 'cold' boot.

However, pressing reset on the black/garbage/random screen results in a normal perfect boot every single time (with either Minerva or JS installed).

Does that mean the CPU (or something) is not resetting like it should do on a cold boot?

[Silvester]

Could be capacitor C4 in reset circuit is defunct.

[Chr$]

Could be capacitor C4 in reset circuit is defunct.

Where did you find that very clear schematic? And is there a board layout of similar quality?

[mk79]

Where did you find that very clear schematic? And is there a board layout of similar quality?

Probably where you find all QL stuff, Dilwyn's page http://www.dilwyn.me.uk/docs/hardware/index.html QLissue6.pdf

[Chr$]

Oh yeah, that's pretty. For some reason I always google it and end up with fuzzy ones. Right, I'll check C4 then.

[Silvester]

Could be capacitor C4 in reset circuit is defunct.

Where did you find that very clear schematic? And is there a board layout of similar quality?

Something I produced back 2014 when I wanted something worthwhile to do in Xcircuit (ie. rendering crappy QL service manual scans into 80K zoomable/searchable PDF's).

No. I didn't do block layout, scans IMO are sufficient (though any volunteers?).

BTW I took some liberties with 'upgrade ROM' mods to simplify issue 6 schematic, but if someone wants to do an authentic issue 5 with patches then I can post Xcircuit PS file and they are free to do the detail (the issue 6 PS is posted on forum elsewhere *).

[Chr$]

Well thanks for that and for this, as C4 was indeed very bad (measuring as 2100pF) and a new one has fixed the issue perfectly. Don't think I've ever had a QL electrolytic go bad like that before.

[mk79]

Something I produced back 2014 when I wanted something worthwhile to do in Xcircuit (ie. rendering crappy QL service manual scans into 80K zoomable/searchable PDF's).

Ah, you did the originals, thanks for that, love em

[Dave]

Something I produced back 2014 when I wanted something worthwhile to do in Xcircuit (ie. rendering crappy QL service manual scans into 80K zoomable/searchable PDF's).

Did you do it from a real Issue 6 QL or from the existing schematic? If the latter, which errors did you fix?

[Silvester]

Did you do it from a real Issue 6 QL or from the existing schematic? If the latter, which errors did you fix?

From existing service manual schematics, a few corrections added (http://www.dilwyn.me.uk/docs/hardware/QLschem.txt). Though one thing I was unaware back in 2014 was in issue 6 the data bus for ZX8302 is direct to CPU (Marcel kindly updated PDF).