UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Sharp MZ-80K help needed on repair

SiriusHardware · 10th Oct 2021, 1:45 pm

The next time it boots up and seems to be running the RAM TEST code normally with the 1-2-3 rolling in the corner, try pressing and flexing the PCB - does that make it crash, does the number in the corner stop rolling?

Looking at the broader picture we can say that it didn't work, then it did very briefly, now it doesn't again. It would be unusual (although not impossible) for an IC to be faulty, fix itself and then break down again so it is more likely that you are looking for a physical-intermittent fault such as a bad IC socket contact or a bad VIA (a through hole connection between the upper and lower side of the PCB) or a fractured or damaged track. You'll only find a problem like that by exercising extreme patience and measuring from every point on each circuit node to every other point on the same circuit node.

This will be made even harder if the fault is connecting and disconnecting whenever it feels like it so it just happens to be working at the moment when you measure it.

10th Oct 2021, 1:45 pm	#260
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,586	Re: Sharp MZ-80K help needed on repair The next time it boots up and seems to be running the RAM TEST code normally with the 1-2-3 rolling in the corner, try pressing and flexing the PCB - does that make it crash, does the number in the corner stop rolling? Looking at the broader picture we can say that it didn't work, then it did very briefly, now it doesn't again. It would be unusual (although not impossible) for an IC to be faulty, fix itself and then break down again so it is more likely that you are looking for a physical-intermittent fault such as a bad IC socket contact or a bad VIA (a through hole connection between the upper and lower side of the PCB) or a fractured or damaged track. You'll only find a problem like that by exercising extreme patience and measuring from every point on each circuit node to every other point on the same circuit node. This will be made even harder if the fault is connecting and disconnecting whenever it feels like it so it just happens to be working at the moment when you measure it.