PCW 9256 temporary horizontal scan issue after cold boot

Started by ElectricAmstrad, 17:42, 18 January 22

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ElectricAmstrad

I have recently re-capped a PCW9256.
Everything works as expected except after being switched off for longer than an hour, the next time the unit it switched on it displays a strange horizonal scan issue.
After about a minute, whatever is wrong has 'warmed up' enough to correct itself and the display continues to work normally.
Any ideas as to what could be causing this?

ElectricAmstrad


For future reference, the problem turned out to be a bad IC401 (UPC1379C) which generates the vertical and horizontal deflection signals.


The traces attached show the incorrect and correct outputs on IC401 pin 8 before and after the IC was replaced.
The schematic shows the wrong location to take this trace (13) from.

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