Random QL glitch: no video signal and refuses to boot

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

Postby tofro » Tue Feb 04, 2020 5:05 pm

Note you don't need to fully remove and re-seat chips to improve contact - Moving the pins even only half a mm in the socket is sufficient to break the oxyde coating.

Tobias


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

Postby Pr0f » Tue Feb 04, 2020 9:42 pm

FrancoisLanciault wrote:
Pr0f wrote:I can answer one of your mysteries at least.

I've been looking at the Hermes code - and the keyclick will work whilst there are spaces left in the buffer - after so may character presses, if nothing is reading the keystrokes out of the Hermes chip - the buffer will fill and no longer accept keys - hence no more click

That tends to confirm that the QL is not operating (as in no processor activity - could be in some tight loop, stalled in some hardware way). If you can operate it with the case undone - you may want to check if the smaller of the 2 large chips near the expansion connector on the right hand side is getting hot - this is chip that produces video - ZX8301, and the only thing I can think might be tied to your video modifications...


Good point. How long is the hermes buffer. In my case, the key clicks stop after excatly 7 strokes, always.

Francois


It's 8 bytes as far as I can tell - so that probably makes sense


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

Postby bwinkel67 » Wed Feb 05, 2020 6:46 am

So I did not have the glitch repeat itself for a few days having the computer sit open on my desk and leaving it on for hours (rebooting and unplugging it intermittently). Tonight I came home and turned it on (still in the open stage) and initially I got nothing and was like "oh boy" and I noticed when I typed I heard no key clicks. I hit the reboot switch and all was normal. Note that previous glitches would not immediately fix themselves so perhaps this wasn't a glitch.

What I noticed is that as I tried to hit the reset I accidentally moved the top part which basically only moved the keyboard ribbons on the motherboard from one side to the other. I remember the first time this glitch happened I opened up the case and the keyboard cable was kinked at the connector and I had to cut it to have it work again (like 1/4 of an inch since the kink was a the bottom). I remember wondering then if that could have caused it but that sort of fault causes keys not to work instead of bridging and causing shorts. I did poke both motherboard ribbon connectors applying pressure in all sorts of ways but nothing happened causing a computer freeze (even turning computer on/off).

I just put it back together to sit near the monitor and no problem though at one point there were a few pixels (maybe a rectangle 10 long and 2 wide) towards the bottom center of the screen. I rebooted again and it went away and I thought, maybe the RGB connector wasn't seated all the way and wiggled causing the screen memory to get some random data but maybe I'm trying to explain away problems. Could that be a sign of a faulty memory chip since screen stuff is in RAM?

Running normally so other than that quick hiccup it's fine. I'm still running in monochrome-composite mode since that is factory -- and to be honest it's such a nice picture I'll give up unfocused color for a crisp signal :-)


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

Postby Ruptor » Wed Feb 05, 2020 5:49 pm

A problem I have seen on a PC was the screws around the CPU were too tight it distorted the board and stopped the computer from booting up. Perhaps there is a dry or broken joint that opens or gets stressed when the box is screwed up. You could try flexing the motherboard gently to see it the problem happens. Do you have any window EPROMS added with your modifications?


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

Postby bwinkel67 » Wed Feb 05, 2020 7:29 pm

Ruptor wrote:A problem I have seen on a PC was the screws around the CPU were too tight it distorted the board and stopped the computer from booting up. Perhaps there is a dry or broken joint that opens or gets stressed when the box is screwed up. You could try flexing the motherboard gently to see it the problem happens. Do you have any window EPROMS added with your modifications?


Thanks for the tip...I will try that. There are only two screws on the motherboard but they are firmly holding the board so that could be an issue. I only have the Hermes chip which plugs in in place of the 8049. I also have an ICE ROM cartridge but currently am not using it.


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

Postby bwinkel67 » Thu Feb 06, 2020 4:23 pm

Poking the board didn't seem to work. It wasn't occurring too many times. I left it on for a much longer time and finally it came back. First the screen went haywire while on. It returned at boot. The case was already unscrewed so I opened it up to get temp readings that were all normal. Next reboot and it finally stopped working again and after 10 reboots nothing. I pushed down on all the chips and I think after one of them it seemed to come back. So I carefully pulled all the chips (7 of them), cleaned all the sockets (isopropyl and a toothbrush) and re-seated them. Just ran it for 6 hours and no issue...was pretty warm at the heat sink -- normal not overly as I'm just pointing out the system had definitely warmed up. We will see if that fixed the problem.

I don't think it was the mod itself that caused the problem but more likely taking the motherboard out and flexing things may have caused a bad connection and hopefully in a socket and not a solder joint.


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

Postby RWAP » Thu Feb 06, 2020 8:26 pm

I have come across a similar issue a couple of times in the past.

One was resolved by replacing the voltage regulator - not sure why.

The other was on a QL fitted with a Super Gold Card. It worked great for a while and then would stop - turn it off and wait 20 minutes - then it worked again.

I decided to check the Super Gold Card (as the QL didn't do this on its own) - when I removed the RAM chips from the Super Gold Card, one left a leg behind! It was obviously a crack in a leg on a chip, which basically was expanding when it warmed up...


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

Postby bwinkel67 » Thu Feb 06, 2020 9:36 pm

Great, thank you. That's two more things to look at if it keeps acting up. Currently no more crashes but I haven't tightened the case back and will leave it open for a week or two. If it glitches again, out come the lighted magnifying classes and I'll go over the board (front and back) carefully looking for loose traces or cracked pins. Then on to the voltage regulator. Hoping it re-seating chips works.

As much as I like working on it I prefer not to be constantly taking it apart as that's how things eventually break. The ribbon cable is a perfect example as I put an unused one (so new) into the QL last fall and already it cracked at one of the pinch points -- I do have a modern membrane but why not get some use out of the original ones until they go. I actually put thick clear tape on both ribbons to give them less flex and more rigidity to prevent those cracks :-/


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

Postby bwinkel67 » Sat Feb 08, 2020 10:34 pm

FrancoisLanciault wrote:I am experiencing exactly the same behavior.


I worry updating this due to being superstitions. However, still now glitch repeat since I re-seated the chips in sockets and cleaned the sockets with isopropyl. Murphy's law suggests as soon as I hit submit on this my QL will go haywire again but hoping I have resolved it. So, perhaps gently pulling all socekted chips and cleaning the sockets might fix your QL as well.


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

Postby FrancoisLanciault » Sun Feb 09, 2020 4:01 am

bwinkel67 wrote:
FrancoisLanciault wrote:I am experiencing exactly the same behavior.


I worry updating this due to being superstitions. However, still now glitch repeat since I re-seated the chips in sockets and cleaned the sockets with isopropyl. Murphy's law suggests as soon as I hit submit on this my QL will go haywire again but hoping I have resolved it. So, perhaps gently pulling all socekted chips and cleaning the sockets might fix your QL as well.


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



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