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1200XL Select, Option, Start issue


JGRAHAM2

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I found a spare GTIA and replaced it. No difference. I doubt it is the Mylar connections to the PCB because the reset works and it uses the same connector. What they have in common is they connect back to the GTIA. I tested connectivity between the carbon pads and the connector strips and it looks good all the way through, so it shouldn't be a broken trace.

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Measured at the apprropriate pins at the connector, I would expect that resistance should be at or near zero ohms when the keys are pressed. The pads on the mylar can be stubborn. I've had good luck cleaning them with a pencil eraser. Another trick I've learned is to put a strip of tape over the top of the Mylar where the lines connect to the pcb so when the plastic key assembly is screwed on the little bit of extra thickness sandwiches the connector together with a bit more force.

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Measured at the apprropriate pins at the connector, I would expect that resistance should be at or near zero ohms when the keys are pressed. The pads on the mylar can be stubborn. I've had good luck cleaning them with a pencil eraser. Another trick I've learned is to put a strip of tape over the top of the Mylar where the lines connect to the pcb so when the plastic key assembly is screwed on the little bit of extra thickness sandwiches the connector together with a bit more force.

I bet if you peel back the white silicon spacer on the mylar you will find a break on the mylar side downstream of the RESET pad going to the START, SELECT and OPTION conductive pads. Be careful, only remove as little of the white casket as possible as you may damage more traces. It is important to return the white spacer back where you found it after repairs.

Edited by ACML
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