Dead QL

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gregtaylor
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Dead QL

Postby gregtaylor » Thu May 10, 2018 3:56 pm

I am trying to get one of my spare QLs ready for sale as I have too many at the moment. Have not switched this one on in many years!

The membrane was shot (the one ribbon almost in two pieces) so have installed new. When I switch on though all I get is a solid black screen. Pressing (blind) F1 or F2 does not start mdv1_.

Anyone any idea of the likely cause. Doesn't look like a memory fault.

Greg


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Dave
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Re: Dead QL

Postby Dave » Thu May 10, 2018 4:08 pm

Every possible avenue is covered exhaustively in this thread: viewtopic.php?f=2&t=1140#p9142

However, if you have done all these things and still have a problem, we'll be right here :)


gregtaylor
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Re: Dead QL

Postby gregtaylor » Fri May 11, 2018 6:36 am

Thanks Dave, Have also downloaded the service book and aim to have a really good play with my oscilloscope passed on to me by my brother. Been looking for a good reason.

Will be back if stuck.

Greg


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Dave
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Re: Dead QL

Postby Dave » Fri May 11, 2018 6:06 pm

We'll be here, ready and waiting. :D


gregtaylor
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Re: Dead QL

Postby gregtaylor » Tue May 15, 2018 4:06 pm

Hi,

Have checked with a logic probe across R, G, B and composite on the 1331. All 4 show the same waveform, regular clock cycles with little or no change. It looks like it is actually sending a steady black (or one colour, at least). I have a horrible feeling this mean the ULA (as it is the dearest) but what do you think?

Greg


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Re: Dead QL

Postby martyn_hill » Tue May 15, 2018 5:53 pm

Hi Greg

Whilst the 8301 remains under suspicion, your latest findings do also suggest that either of the DRAM or else the bus transceiver (that inter-connects the CPU bus to the 8301's 'private' bus isolating the DRAM) might be shot.

I don't believe the replacement 8301 is too expensive - assuming Rich (of RWAP) still has some stock available...

In my experience, building up a small collection of some of the more common ICs used in the QL to use in a 'repair by replacement' approach saves a lot of time. Some of the replacements would require re-soldering but many of the usual suspects are socketed for easy drop-in replacement.

Do you have the relevant QL schematic to hand (Iss 5 or Iss6)? Another invaluable resource in your tool-kit to get the QL back to health and available for download from Dilwyn's QL repository.

Matching your observations against the various symptoms already posted in the thread that Dave referenced should help focus your efforts.

Good luck!


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tofro
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Re: Dead QL

Postby tofro » Tue May 15, 2018 6:25 pm

martyn_hill wrote:my experience, building up a small collection of some of the more common ICs used in the QL to use in a 'repair by replacement' approach saves a lot of time.


Right. It also seems to be a fundamental law of something that a chip you have a replacement for is never going to die again ;)

Tobias


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Dave
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Re: Dead QL

Postby Dave » Tue May 15, 2018 7:37 pm

tofro wrote:Right. It also seems to be a fundamental law of something that a chip you have a replacement for is never going to die again ;)


Given the high number of Italians here, this seems appropriate:

Heeeey, that's a nice 8301 you got there. Would be a shame if something, you know, happened to it... But look, I can save you a looooot of trouble my friend.... See, I have an 8301... And you could, you know, "protect" yourself for the low low cost of £99...

Per month!


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Dave
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Re: Dead QL

Postby Dave » Tue May 15, 2018 7:55 pm

All joking aside, though, 8301s being damaged by their unprotected RGB inputs is a HUGE problem.

My new RGB and S-Video board provides full protection against those kinds of shocks. It's already tested and working as a system - I'm just trying to get it to fit in the weird space that is available. I have to slip a very compact connector out of the slim gap through the ROM port, which is a challenge. That said, I have designed a nice little case for it that matches the QL perfectly, and am doing a version of it for the new QL-SD cards that are coming soon from another person. I could do a combo case so you'd have dual SD and clean RGB and S-Video and Composite, all in one nice slim matching black case.


gregtaylor
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Re: Dead QL

Postby gregtaylor » Sun May 27, 2018 7:56 pm

Thanks to all. Finally found time to very carefully move the 8301 from my working QL to the failed one and voila - microdrives spin, screen works, everything!!

Have found a supplier so just a matter now of purchasing a new 8301 and both will be back into full working order.

Now i just need to fix my oscilloscope which is not working properly.... I have a hobby electronics USB data analyser which works fine. I would heartily recommend them.

Greg



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