On 2/20/22 01:28, Lincheng Xiu via groups.io wrote:
After 6 hours troubleshooting, it is fixed. The reason is C35 short. 100uF/50V electrolytic capacitor.
Here is what I traced the partial schematic of HP83751A power supply.
?After C35 short, the PWM controller does not drive the MOSFETs.
Also checked the ESR of C1, which is too much, 2 ohm, it will soon fail, just replaced with a new one.
Wow, I see electrolytic capacitors like that dry out and lose capacitance all the time, but I don't think I've ever seen one shorted. Nice troubleshooting!
-Dave
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Dave McGuire, AK4HZ
New Kensington, PA
Dave McGuire