Tek 7904 Power supply help

[Bill Riches]

I have been working on my 7904 power supply for way too long!  I  would like to talk with someone that knows and has repaired these units.  Thank you.

Bill Riches, WA2DVU
Cape May, NJ
bill.riches@verizon.net

[med6753]

I have. When I bought my 7904 it was ticking like mad. Issue turned out to be a shorted tantalum capacitor on the -17V bulk supply. What is your supply doing? Blowing fuse? Or just completely dead? Or trying to come up but going into tick mode?

I have a document specific for troubleshooting the 7904 PSU but it is too large to attach here. Send me an email at seanfinn999@gmail.com and I'll send it to you.   

Edit...oops...just noticed you provided your email. I'll send you the document.

[madao]

i have  repair two  7904 PSU.  Both is failed with odd reason.

One runs only up to 170V Input (by 230V setting), then fuse blow.  One  940µF of two series is shorted.



other PSU run  with two simple plugin with sometime starting issues.  Four plugin,  it starts sometime , if PSU is warmed up.  It make noise "SUMMMM ! SUUMMMM! ", not ticking !

Reason:  two  power transistor  in primary side is semi-broken (to much less current gain by  higher current, less than 4 ßeta ), if transistor is hot, it hat gain of "a bit over 4" --> stable oscillation.
Transistor swapped , then  it run  stable. I have replace him with 2N6678.



Greetings
matt