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Old 10 November 2018, 14:00   #21
alphagemini
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I have now tried with another HD and even booted from a new floppy. Nothing comes up on screen. Si it would appear that the circuitry controlling the video output is in trouble. Is there a graphics chip that can fail? If so where is it?

thanks for any help
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Old 10 November 2018, 21:57   #22
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There are a couple of chips involved. If you're not getting anything from composite or SCART, you could be having issues with the DAC, the encoder, or one of the other parts involved. Given that the whole signal has stopped working (rather than another fault like a colour being wrong), it's possible that one of the sync traces has been damaged, or a part related to the sync signals has failed, meaning the signal isn't usable by the display.
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Old 10 November 2018, 22:13   #23
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Nobody can test equipment that they don't have access to. If *you* made the determination that there was a motherboard problem (but the problem was actually your power supply or video cable), and you just send in the motherboard, then the service department can ONLY test the motherboard.

The question now becomes, do you actually want your setup fixed? If you do, you'll ship the computer (including everything you have hooked up to it, hard disk as well), power supply, and scart leads. Or, you can find someone else with a working setup and borrow a *known working* power supply and video lead (DO NOT ATTEMPT TO POWER THEIR COMPUTER WITH YOUR POWER SUPPLY) for a few days.

It sounds like you are having a mainboard problem, but its best to be sure to send the power supply in to make sure the 5V rail isn't drifting around when it warms up.
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Old 10 November 2018, 23:45   #24
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Completely guessing at the point without seeing it.


It could these as everything else is ruled out;


1) HDD, but even with it disconnected, it should show kickstart screen withing 15 secs (if I recall, it has 3.0 roms).


2) Scart wasn't pushed in square and the sync or RGB signal was not making contact. However this should not effect Composite.


3) Scart wasn't in square and thinking it was cable, started pulling it in and out at computer end. Where by blowing the ferrite beads for video output. Seen this alot of times, where people have shorted 12v out while fiddling to get rgb connector in.


4) Blown protection circuit on TV end. I have seen this once before on Samsung TV. However other TV's have been tried.



5) PSU, but I would think it would effect more things than just video output.
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Old 11 November 2018, 00:49   #25
alphagemini
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Thanks everybody for your replies. I can get some things tested tomorrow.

I will have to buy another 1200, money and time passing. If I can get mine fixed without it costing too much it will be a standby.

Thanks again.
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