The Sinclair QL Forum

Fixed it! Thanks to Pr0f for directing me away from the primary side of the PSU as there was nothing wrong with it! I measured D512 and it had no voltage. Unplugged the next most important board along (the Chassis board II) and the diode showed 5v. Tested again on the EPROM that is on the PSU board ...

Using my crude methods the new thyristors test very similar to the removed part. So I'll fit a new (NOS) one and will then test voltages at various places on the secondary side. What I can also do - as various other boards are plugged into the main PSU board - is remove some/all of them and see if t...

I ordered a couple. Cheap enough and easy to swap.

If you have a multimeter with a DC input voltage rating of 500v or higher - you should be able to measure across the main capacitor - on DC voltage range - you should see some 350-400V. You could also check the stripe (cathode) side of the rectifiers on the secondary side - these should give some i...

My 'scope isn't rated for that high. I wonder if that new big cap is crap.

I get 320v across the big cap (C395) but from the cap negative to pin 5 of the transformer (the circled test point no.1) the multimeter throws a fit but did briefly show around 11v. Not 400v!

So that seems to confirm that the issue (assuming it's the only issue) is on the primary side?

Thanks ever so much Pr0f. There is indeed an illustration of what to expect at those circled points: GrundigPrimary2.jpg Before I dig out the oscilloscope, circled no.1 should be approx 400v and it's one of the winding ends (the 5 between 5 and 3). But I assume it should be 400v between circled poin...

I know there are some expert electrical gurus here so thought I'd post this issue... This schematic is the primary PSU side of a 1993 Grundig GV280S VCR. Mains comes in at the top, optocoupler bottom right and you can just about see the secondary windings along the bottom. GrundigPrimary.jpg I bough...

t0nyt wrote: ↑Mon Apr 08, 2024 6:24 pm My mother was born 1926 (still going too)

Bless her.

One of mine was, but only just (1900). The others were 1915 and 2x 1926.