Sinclair QL - blank screen.... HeLp!

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XorA
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Re: Sinclair QL - blank screen.... HeLp!

Post by XorA »

abraXXious wrote: unfortunately I do not have access to a logic probe so I am going to have to try and test/replace the logic chips one at a time.
That can be rectified pretty easilly these days.

http://www.ebay.co.uk/itm/USB-Logic-Ana ... SwbYZXame3


MartynHill
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Re: Sinclair QL - blank screen.... HeLp!

Post by MartynHill »

Hi Steven

The HAL IC only came in to play on Issue 6 & 7 boards, so if you can't find that, its an Issue 5, which used standard 74-series logic chips that were later replaced by the HAL.

Can you take a picture of the board and upload it here?

As a REALLY cheap and cheerful Logic probe/analyser, I have successfully used a device available from Hobby Components in the UK which connects via USB to a PC and you then run an open source piece of SW called PulseView to monitor the 8 available I/O pin-states.

Good luck - it can be really satisfying to get a limping QL to function again - especially if the casing/keyboard etc is still in good condition.

M.


Derek_Stewart
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Re: Sinclair QL - blank screen.... HeLp!

Post by Derek_Stewart »

Hi Steven,

The order to test replace is hard, as the defective chip could be any of them.

If you can remove the chips without damaging them they can be tested on a IC Tester. I have a couple of Eprom programmers with IC Chip testing facilities incorporated.

Although there are in-situ IC testers that can be used with the chip still in place. But the results are sometimes confusing with the chips still soldered in.

Without testing each chip to find the defective one, you could try changing them all, TTL chips should not be too expensive.


Regards,

Derek
abraXXious
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Re: Sinclair QL - blank screen.... HeLp!

Post by abraXXious »

Thanks guys. I will look into the logic probe.

There appear to be no HAL or PAL chips - all seem to be off the shelf logic ICs (which is good in my case - cheap and easy to replace when I find the faulty one).

Please find a picture of the board. Please excuse the quality, I took it in a hurry. ;)
Attachments
QL.JPG


Martin_Head
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Re: Sinclair QL - blank screen.... HeLp!

Post by Martin_Head »

A couple of points come to mind which I don't think has been mentioned yet.

Check for bent pins on the expansion port down the side of the board.

Check the reset button is working, and not causing the QL to be constantly reset.


abraXXious
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Re: Sinclair QL - blank screen.... HeLp!

Post by abraXXious »

Thanks Martin. Checked the expansion port - all good. Tested the reset button - all good.


martyn_hill
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Re: Sinclair QL - blank screen.... HeLp!

Post by martyn_hill »

So that's one of the later Issue 5 boards - after the switch from 'piggy-back' EPROM to mask-ROMs.

You can see a space where another 74-series IC was used to help in the EPROM decode that then got consumed into the custom-masked ROMs themselves.

One thought:
The 15MHz crystal clock oscillator can become damaged as it sits proud of the board and can be fairly cheaply and easily purchased/re-soldered.

If that isn't toggling the clock, you might see the behaviour you have observed as it operates both the Master Chip (MC - 8301) and in turn, the CPU Clock. Its stood upright, horizontal, mid-way back on the board, just right of the MC itself and is a metallic silver can shape.

There's another similar oscillator running at 11MHz between the 8302 'Peripheral Chip' and the 8049 IPC. Possibly worth replacing that as well, as its pretty straightforward.

Don't worry about the smaller cylindrical can oscillator right next to the 8302 - that's a 32KHz that simply runs the 'real-time' clock (and 'tuned' by that variable capacitor with the small screw protruding from the top - something else they did away-with in later boards.)

Good luck!


abraXXious
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Re: Sinclair QL - blank screen.... HeLp!

Post by abraXXious »

Hi Martyn,

good call on the oscillator crystals - I had an Amiga 1000 once arrive not working even though it was purchased working and shown as such. Turned out to be the clock crystal which had just died in transit (hard bump or vibration perhaps?). Replaced the crystal and off it went. This QL was purchased working, yet arrived dead.... I wonder....

Anywho have purchased an 11 and 15 mhz crystals. Will update when they arrive.

Thanks again,

Steven.


Martin_Head
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Re: Sinclair QL - blank screen.... HeLp!

Post by Martin_Head »

abraXXious wrote:I have substituted every socketted chip from the working QL to the non-working unit and there is no change, so it is not one of the socketted chips.
Have you tried the chips from the non working QL in the working QL to prove they are OK?

As you only seem to have a multimeter for testing. Something you could try, which is a bit long winded and not overly accurate. Is to take the working QL and measure the resistance of all the pins on the IC's relative to ground. Write them down on a piece of paper, and compare them with the non working QL. Looking for any major discrepancies.


abraXXious
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Re: Sinclair QL - blank screen.... HeLp!

Post by abraXXious »

Thanks Martin, some more good avenues to explore - will start that this weekend and post back results.


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