My 7800 repair thread

[+bent_pin]

I have a pile of 7800s to repair. To keep from polluting the forum with many threads, I figured I'd jut make one running thread to use from one repair to the next.

 

The first unit that I'm working on works perfectly except for the power latch circuit. If I weight the power switch down the unit works without issue, but as soon as the switch is released, the power is cut. I think it's the CD4013 latches that have failed. Here is the schematic:

Has anyone else had and corrected this issue before?

[+-^CrossBow^-]

48 minutes ago, bent_pin said:

I have a pile of 7800s to repair. To keep from polluting the forum with many threads, I figured I'd jut make one running thread to use from one repair to the next.

 

The first unit that I'm working on works perfectly except for the power latch circuit. If I weight the power switch down the unit works without issue, but as soon as the switch is released, the power is cut. I think it's the CD4013 latches that have failed. Here is the schematic:

Has anyone else had and corrected this issue before?

Not this exact issue no, but the 4013s are a common failure point with something similar in the 5200s so it isn't a bad place to start and is a cheap enough part to replace. This might even qualify to piggy back another 4013 on top to see if the behavior changes to give you a better idea.

 

 

[+bent_pin]

4 minutes ago, -^CrossBow^- said:

Not this exact issue no, but the 4013s are a common failure point with something similar in the 5200s so it isn't a bad place to start and is a cheap enough part to replace. This might even qualify to piggy back another 4013 on top to see if the behavior changes to give you a better idea.

 

 

Nice. I have loads of CD4xxx. I'll dig one out and see.