Random QL glitch: no video signal and refuses to boot

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bwinkel67
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Re: Random QL glitch: no video signal and refuses to boot

Postby bwinkel67 » Fri Feb 21, 2020 3:46 am

FrancoisLanciault wrote:I have not yet opened my QL (lack of time). But sure, the first thing I will try will be to check the socketed chips. Hopefully it will be just that. I will let you know.

François


Have you had any luck fixing yours. It's been almost 2 weeks and mine hasn't glitched since so the deduction that futzing with the motherboard (i.e. I had to remove it) likely moved something that caused one of the socketed chips to lose full contact. Grabbing the 9-pin signal off of MC1733 for color composite wasn't causing the issue.


FrancoisLanciault
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Re: Random QL glitch: no video signal and refuses to boot

Postby FrancoisLanciault » Fri Feb 21, 2020 8:11 pm

bwinkel67 wrote:
Have you had any luck fixing yours. It's been almost 2 weeks and mine hasn't glitched since so the deduction that futzing with the motherboard (i.e. I had to remove it) likely moved something that caused one of the socketed chips to lose full contact. Grabbing the 9-pin signal off of MC1733 for color composite wasn't causing the issue.


The only thing I have done so far is to open the QL and re-set the chips in their sockets. No joy. Unlike you, the problem is not intermittent. The QL is simply totally dead with the exception of the power LED and Hermes that clicks when a key is press until its buffer fills.

I have been using QLs since the first days and have had many problems with them, bad contact, etc, but every time something could be seen on the screen (garbage) often accompanied with terrible sound coming out of the speaker and wild running microdrive motor. It is the first time the QL is dead like that.

Next step is to remove all adds-on and try again with a BBQL config. However I am beginning to fear of a bad ZX8301, which would explain the lack of image and processor activities.

I would gladly accept some guidance as to what to probe to check the health of the ZX8301 and other support chips.

François


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bwinkel67
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Re: Random QL glitch: no video signal and refuses to boot

Postby bwinkel67 » Fri Feb 21, 2020 9:21 pm

If putting it back to BBQL doesn't fix it then yes, replacing chips is the easiest. You could put a volt meter on to see if signals are flowing but that requires a bit of knowledge of which pin on which chip wants what -- not impossible but you have to read the circuit diagram for the motherboard and/or the pin-out of each chip. Then, applying an oscilloscope to figure out what the chip is doing could be the next step. I have very little expertise in any of that (and don't even own an oscilloscope) but would like to get better at it. I watch Adrian's Digital Basement on YouTube pretty regularly and he does a great job showing that stuff though he claims he's not an expert (and not on a QL but on Amiga's, C64's, etc...).

As for replacement chips,which would have been my first approach, you can get them pretty cheaply from a seller on SellMyRetro. The ZX8301 is becoming rare so you might want to get one, see if it fixes things, and then get a second one as a spare -- I added a spare this year. I also try to be careful how I plug and unplug things since some of the chips (video esp) aren't buffered. I do want to add some protection to my video via zener diodes so that will likely be my next task (starting summer when I have more time)

But I think that likely replacing chips will be your best (and quickest) route to fixing it since in a way, re-seating chips kind of does the same thing: the chip has a bad contact so it doesn't work properly and re-seating it fixes the contact and the problem vs the chip is broken and doesn't work properly so replacing it will fix the problem -- in my case I was lucky and the chips were ok but one had a bad contact.

Keep us posted and good luck bringing it back to life!!!



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