Hi From London England

[Ruptor]

Is my QL one of the early ones with a serial number of D14 071480? I assume 71480 is the number built but how many were built by the time production stopped? If it is an early one does that mean I need to do mods on it? I don't remember there being any problems with it when I used it in fact compared to the DEC 11 we had at work the QL was ultra reliable. Just imagine if it had proper disc drives to start with we might be using QL derivatives today instead of PCs but I guess Sinclair computers would have been bought out by the Americans to stop the competition like they did with INMOS and the Transputer.

[Chr$]

Is my QL one of the early ones with a serial number of D14 071480? I assume 71480 is the number built but how many were built by the time production stopped? If it is an early one does that mean I need to do mods on it? I don't remember there being any problems with it when I used it in fact compared to the DEC 11 we had at work the QL was ultra reliable. Just imagine if it had proper disc drives to start with we might be using QL derivatives today instead of PCs but I guess Sinclair computers would have been bought out by the Americans to stop the competition like they did with INMOS and the Transputer.

No, that's a fairly late one. It started with D02-XXXXXX and the D number denotes the month number, not 'DECember'. You probably have an issue 6 (the latest as far as I know, apart from the Samsung German/US ones). They sold approx. 100k UK models.

With a proper FDD it would have been more expensive and may not have sold 'as well'. But you're right, even back then the Americans were very powerful/influential, whatever really good ideas that foreign companies had would have probably ultimately been taken over or quashed in some other way.

[Ruptor]

No, that's a fairly late one. It started with D02-XXXXXX

That is good it will have less bugs & mods then. Unfortunately I plugged it in, tuned the TV in to what looked like a computer screen but it was a sparkly green interference screen not changing when buttons were pressed. Um! I think the computer is dead. I stuck a voltmeter on the pins and two read a lot of AC at 16.7V no DC so I am off to find the circuit for the PSU. Service manual I suppose.

[Chr$]

Hopefully it's the PSU then and no damage done. Open it up, there're not that complicated. I serviced one and changed the 2 fat caps the other day.

[Ruptor]

No circuit in the service manual. I have opened it and it looks weird. An SCR and two diodes stuck on windings opposite to the main PCB what is it all about. The caps are not blown or shorted. There seems to be 10.75V on each cap & between two pins on the power lead but the 44V AC is reading 16.7V. I will have to see where that comes from.

[Chr$]

Around 16v AC sounds about right for one of the required voltages. There should be about 16v AC and 9v DC and on the plug the middle pin is GND.

More here: viewtopic.php?f=2&t=1231

[Ruptor]

I checked the supply with a scope and on the output pins there is a 44V AC wave and 10.8V DC so could it be the 9V supply that is causing the problem? I would have thought the regulator for 5V could take a minimum of 12V input since many handle up to 35V. Having opened the supply and put it back together the QL still gives a green screen but this time holding the switch on the right it gives morse code like vertical lines every half inch across the screen. When the button is released there is a click as if something is being initialised so there has been a change compared to the first turn on but still the pale green screen that is slightly more stable and clear. It looks like I will have to open the QL up to make progress.

[Chr$]

I'm afraid I don't know. 44v AC seems very high.

Vertical lines could be a ram prob, or something else. The click is certainly the little speaker. They always click when you reset with the button on the right. No doubt someone will be along who knows a lot more about these things, once they've slept off the Christmas pudding.

[tofro]

44V VPP measured with a scope is about 15.5V RMS - So, fine. Typically, voltages will go down a bit anyways under load.

The 10.8 Volts also look OK.

You really need to have a look inside. First thing to check is IC sockets - contact between sockets and ICs gets worse because of time and corrosion - simply remove and re-seat the socketed ICs.

Tobia

[Ruptor]

You really need to have a look inside. First thing to check is IC sockets - contact between sockets and ICs gets worse because of time and corrosion - simply remove and re-seat the socketed ICs.

It looks like it has just come out of the factory but I jiggled the chips about that sit in sockets and it made no difference. The 5V is on the regulator and the TTL chips. Since the RF video output is working and displaying the ram contents it is reasonable to assume its power is there and any power to the microdrives is irrelevant to booting I think but no sure. Any other suggestions as to where the fault might lie given the symptoms are welcome. A weird thing happened when I touched pins on the processor around pin 1 the system seemed to do the power on click but several times. It never did it again which is weird since if there was a sensitive signal one would expect it to always be sensitive and I thought it might be floating but still no difference to the pale green screen.