i replaced the diode, and there was no short anymore connecting the meter leads to the terminals in either way. good news.
i used my dca55 to test the 2n3055 transistor at the back, and it said it was ok.
i fired up the power supply, and it worked. powered a 12v bulb fine for a few minutes. then i switched over to charging a 12v battery @ 13V, current limited to 700ma (the c20 rate of the battery).
all looked fine and dandy for a few minutes when suddenly white light and a burning sound came out of the side of the power supply. christ, thats never happenned before. switched it off and pulled it open again.
There appears to be a small cap blown on the circuit board. it is connected across the two ac rails that come from the transformer, then through 2 relays, then into the bridge rectifier. the cap is across the input to the bridge recifier. I have no idea why. because normally any signal smoothing is done with a cap on the output of the bridge rectifier. and its a tiny cap, so i dont know how it would fullfill that purpose even though its in parallel with the transformer, so it might be a resonant/filter of sorts. i know nothing about those guys.
is anyone able to chime in here on anything else i should look at? what might be a problem?
its strikes me as odd because before i identified a cracked diode on the dc output. but this cap has burst into flames on the ac input to the bridge rectifier, probably already stepped down from 240v to something like 36v. I don't understand the connection between these two events.
unless some how the shorted dead diode damaged the cap before. im stabbing in the dark.
in any case, i dont think replacing the cap is going to solve the cause. i fear its just a symptom.
@spitso: do you think you could tell me the value of the cap im talking about? it is c5 on the board. mine has been rendered unidentifiable.