QL doesn't work: black screen

[1024MAK]

TV/monitor screens black. Power light on. Fails to power-up. Check voltages (para 2.2.3)
<snip>
Ah, the "power light", where is it? In the PSU or in the QL?

That's the yellow one on the bottom left of the keyboard. It is supplied from the +5V line.

After you have switched on, does anything happen if you press F1 or F2?

Also earlier we were talking about the heatsink for the 7805 voltage regulator. The only special thing about the heatsink in the QL, is it is designed to fit in the case. Richard (RWAP) may be able to sell you a spare. He also has various other spares. See SellMyRetro. In the meantime, any large aluminium heatsink will do. If you mount the regulator away from it's current position, ensure {double, no triple check that the middle lead (0V) is properly connected}. Failure of the 0V connection to a 7805 regulator will result in an excessive output voltage to the QL circuitry, which is likely to kill semiconductors

If I get time tomorrow, I will have a look at the schematic to see what else the +12V and the -12V lines feed.

Mark

[Dave]

The +/-12v is only used by the serial ports, to my knowledge. In my US QL, the microdrive motors receive 9V DC from somewhere but I have never looked where.

[Bubu]

That's the yellow one on the bottom left of the keyboard. It is supplied from the +5V line.

Argh, I've been for 10 minutes looking for such a led, and I can't find it. Is there any pic showing this led? Perhaps it has been removed from my QL...

After you have switched on, does anything happen if you press F1 or F2?

The ribbons look not quite good, so I'll have to shortcircuite the pins in J11 and J12 as shown in this schema:



but I'll do ASAP and I'll tell you. I understand that I have join the following pins:

F1: J11=1 and J12=3
F2: J11=1 and J12=4

If I get time tomorrow, I will have a look at the schematic to see what else the +12V and the -12V lines feed.

I'll be very grateful, thanks!

[Bubu]

The +/-12v is only used by the serial ports, to my knowledge. In my US QL, the microdrive motors receive 9V DC from somewhere but I have never looked where.

Yep, as I can see each microdrive has its own 7805, so we only have to follow the feed line, I'll do it

[vanpeebles]

Photo of the white power led I fitted into mine, in it's standard location

[Bubu]

What the...? Is there a led in that place?

This is behind the keyboard in my QL:



As you can see, there's only a gap in that place. So this led is missing in my QL... OMG... Well, where is this led supossed to be connected to?

By the way, vanpeebles, your QL is modded to white, isn't it?

[Bubu]

OK, I answer myself. My QL has none of these 3 leds:



Well, that's a minor problem, I can easily put 3 leds and go

[Bubu]

And lastly (sorry for the 3 consecutive posts) I've measured the pins where it's supossed to be my yellow led, and when I turn the QL on, there's 5V in those pins, so the led would be on

[Bubu]

News!! News!! ( and 4th consecutive post ) If I short the pins to make a F1, I heard as if the microdrive engine works. There's life in this QL!! (isn't it?)

[1024MAK]

So it looks like the major problem is the video circuitry...

Mark