Spy Hunter linear power supply help

DogP

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Hey,

I picked up a dead Spy Hunter recently, and I've narrowed down the problem to the linear PS (swapped it w/ a good one). Typically these are pretty easy to diagnose, but I'm having issues tracking down the problem on this one. It's physically in great shape w/ no acid damage. Basically, the +5V is low, and resistor R104 (10ohm 5W) gets REALLY hot.

I pulled/tested all the transistors on the +5V rail (Q103, Q104, Q105), and even swapped them after they all tested fine, and I also swapped U2, but nothing seems to make a difference. Has anyone had a similar problem, or have any ideas?

I'd really like to repair this rather than using a switcher adapter.

Thanks,
DogP
 
Thanks for the reply... I did check all the caps (just w/ a multimeter) to verify they weren't shorted, but didn't find any suspect. Both C110 and C111 test perfectly fine. Any other ideas?

Thanks,
DogP
 
Check the waveform on the 5v. Choppy input voltage can mess with the regulator circuit. Also if theres a zener diode, measure the voltage across that.. Could be a resistor around the zd.. Good luck!

Andrew
 
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