QL doesn't work: black screen

[Bubu]

Hiiii

I've just come to this forum and I've been quite welcome

The thing is that I was given a QL that, obviously, doesn't work. It has no PSU, and I buit one just taking a 9V PSU and using a special connector I could given the 9V to the QL:



But when I turn on the PSU, an excellent black screen is shown in the TV
And nothing else happens...

I did this twice. And the 2nd time it happened something: suddenly, a serie of random loud beeps sounded (I almost fall down from the chair)

This QL has no heat sink inside. Anyway, do you know where should I get measurements of volts as I can check if at least the voltages are OK?


Thanks in advance!

[Bubu]

(ooops, the pic doesn't fit the forum!!)

[1024MAK]

The 7805 voltage regulator needs a heatsink in order for it to dissipate the heat it generates. If it does not have a suitable heatsink, it will shut down. However, running the QL like this risks damaging the 7805, as the sharp and rapid cool - heat cycle is not good for it.

As viewed in your picture, the left hand leg of the 7805 should be a DC voltage of at least 8.5V. The right hand leg should be between 4.75V and 5.25V. Both these voltages are respect to 0V which the centre leg and the heatsink tab on the 7805 are both connected.

I assume that you are aware that the power input is a three pin connector and as well as 9V DC, the QL requires a AC line so that two further voltage regulators can generate +12V and -12V rails. These are mainly used by the serial ports, but IIRC one of them is also used for something else (could be a mod that was recommended).

Edit: there is some power supply information in this thread. If you search you may well find more information.

Mark

[Bubu]

The 7805 voltage regulator needs a heatsink in order for it to dissipate the heat it generates. If it does not have a suitable heatsink, it will shut down. However, running the QL like this risks damaging the 7805, as the sharp and rapid cool - heat cycle is not good for it.

Yep, the thing is that this QL came without a heatsink... Do you know where can I find one? Or could I build one with pieces?

As viewed in your picture, the left hand leg of the 7805 should be a DC voltage of at least 8.5V. The right hand leg should be between 4.75V and 5.25V. Both these voltages are respect to 0V which the centre leg and the heatsink tab on the 7805 are both connected.

I'll see if these volts are ok in this QL, but I think so as the computer boots, but not the OS. I heard once a serial of beeps

I assume that you are aware that the power input is a three pin connector and as well as 9V DC, the QL requires a AC line so that two further voltage regulators can generate +12V and -12V rails. These are mainly used by the serial ports, but IIRC one of them is also used for something else (could be a mod that was recommended).

OK, 1024MAK, I have no PSU for the QL so I had to build one for booting up at least. I thought that 12V were only used for microdrives, so I don't mind at the moment. I prefear now see if this QL works or not, I mean, if customs chips are dead or not.

Edit: there is some power supply information in this thread. If you search you may well find more information.

Thanks, 1024MAK, first of all I'll check the voltage in the 7805

[vanpeebles]

In the past people have mounted the regulator on the outside of the case, fitted to an old PC heatsink or similar

[Bubu]

It's a good idea! Although I'll replace the regulator by a Tracopower, I can do that meanwhile

[Bubu]

I've just measured the pins of the 7805, and it's okay:

IN: +8.8 VDC
OUT: +4.9 VDC

Which other pins could I measure to determine if chips are well fed?

[Dave]

Do you have an oscilloscope?

[Bubu]

I'd like but not yet, I'm looking for one since 2 years ago as I'm repairing Jamma boards too.

I only have a polymeter (is it well said?). By the moment I suspect that some chip is not receivig the right voltage. Which pins should be measured first of all?

EDIT: Ah, I forgot it, I also have a logical probe

[Bubu]

Searching and searching and searching again I've found this:

http://www.sinclairql.net/srv/qlsm4.html

In a table is shown this:

TV/monitor screens black. Power light on. Fails to power-up. Check voltages (para 2.2.3)

Renew IC22
Renew IC24
Check RAMs
Renew IC34
Renew IC18
Renew IC33


So I have something that I can check I'll tell you the results!

Ah, the "power light", where is it? In the PSU or in the QL?