QL doesn't work: black screen

[vanpeebles]

Sounds like you are getting closer Yes my white QL is a custom job I wonder who pinched your LEDs and why?

[Bubu]

That's what I'd like to know too What I imagine is that the last owner thought this QL didn't work and used it as pieces. As far as I know there are 2 missings thigs: the heatsink and the leds.

Well, coming back to the problem, if the failure is the video, which chips are involved, and how could I test them? I hope no custom chip was in that black list...

[RWAP]

I have all the bits and pieces you need.... (including the original LEDs etc)

As the QL microdrive motor runs when you press F1 - the QL is working as such.

Are you trying to view it using a television or TTL monitor? It might just need a replacement MC1377P chip.

[tofro]

Some of the "usual suspects" would be:

• IC28 (MC1377)
• TR9 (The video mix transistor)
• ZX8301 (ULA1, custom chip, but can be had through Rich Mellor)

In the given order.
It would be worth knowing if it's only the TV out that doesn't work (so you should probably try the RGB connection first). IF RGB works and Composite/TV doesn't, that would point towards the mixer circuitry.
Sync signals seem to work, though, as you wouldn't even get a black picture without them.

Hope this helps a bit forward.

Tobias

[Bubu]

I have all the bits and pieces you need.... (including the original LEDs etc)

As the QL microdrive motor runs when you press F1 - the QL is working as such.

Are you trying to view it using a television or TTL monitor? It might just need a replacement MC1377P chip.

Thanx for coming, Rich! But you told me once that you have nor heatsinks neither PSU's, have you?
I'm using a CRT television

Some of the "usual suspects" would be:

• IC28 (MC1377)
• TR9 (The video mix transistor)
• ZX8301 (ULA1, custom chip, but can be had through Rich Mellor)

In the given order.
It would be worth knowing if it's only the TV out that doesn't work (so you should probably try the RGB connection first). IF RGB works and Composite/TV doesn't, that would point towards the mixer circuitry.
Sync signals seem to work, though, as you wouldn't even get a black picture without them.

Hope this helps a bit forward.

Tobias

Thank you for your ideas, tofro. Using the RGB connection it's quite difficult for me as I don't have the appropriate cable, but I'll try it...
Meanwhile, could I test the IC28 in any way? (volts, electric continuity, logic probe...)

[tofro]

If you happen to have an oscilloscope, you could be looking first for the composite signal (should be an irregular signal on top of the regular sync, between 0V and 2V), and then the single-color "R", "G" and "B" signals. If you see single color and sync, but no composite, it's likely to be the mixing circuit. In all other cases, I would first try and replace the MC1377.
But as you're apparently seeing a synced black screen, that hints to working sync signals, and so I would suspect the 1377 as the culprit. But that's simply a guess from afar.

Tobias

[RWAP]

I have heatsinks, LEDs, 1377., 8301, 8302, 8049 chips, membranes etc...

I did say that I had heatsinks (I am sure) - ....

The only thing I don't have are any spare power supplies unfortunately....

[Bubu]

(...) and so I would suspect the 1377 as the culprit. But that's simply a guess from afar.

OK, tofro, the focus is on the 1377. Mine is a MC1377P, I guess that "P" stands for "PAL"
And now the thing is, how the f* should I extract this chip from the PCB? It's terrible!!
I think I'll use a staple remover:



but I have it in my work office, and it will be tomorrow

For today I'd like to get the pinout of this chip in order to see what can I measure

Thanksssss

I have heatsinks, LEDs, 1377., 8301, 8302, 8049 chips, membranes etc...

I did say that I had heatsinks (I am sure) - ....

The only thing I don't have are any spare power supplies unfortunately....

Argh, Rich, I understood you didn't but anyway, the postage costs from England to Spain are prohibitive to me, so... I'll try to do it by myself (but the PSU). To solve the heatsink, I'll replace the 7805 by a tracopower. And about the leds, it's easy to replace them.
Other question is the membrane... it's broken. I'll try to patch in a way that I've patched a Speccy.

If we find out the fail chips, I'll ask you

But the PSU...

[Bubu]

And this is the 1377 pinout. I have to look at pin 14, that must be 12 volts... ummm... I'll tell you tomorrow!!

[1024MAK]

QL power arrangements

Most of the board uses the +5V supply, which comes from an on board 7805 supplied by the +9V rail.
The microdrive circuitry and motors uses the +9V rail (the microdrive ULA boards each have an on-board 78M05).

There are also +12V (78L12) and -12V (79L12) regulators on the main board. These supply the following:-

+12V used by:
Serial ports IC25
Composite Video (which feeds the UHF modulator), MC1377P, IC28

-12V used by
Serial ports IC25
The extra modification to improve microdrive operations. See service manual.

So as the MC1377P colour encoder chip has no supply, that would explain your black screen

If you do not have a suitable 15V AC supply, you can feed in +15V dc but only the postive (78L12) regulator will work. But it should power up the MC1377P colour encoder chip

I hope this helps.

Mark