Most likely you have a rectifier diode that is burned to short,
or a filter capacitor that has created a short. When a shorted
rectifier diode puts AC onto the electrolytic capacitor filter,
it shows as a dead short, and can burn the molex connector up.
The electrolyte from electrolytic capacitors is very low resistance,
if it leaks out of the bottom of a capacitor to a circuit board, it
can short out the circuit board to very high current.
-Chuck Harris
Raymond Boute wrote:
toggle quoted message
Show quoted text
My HP3586A suddenly lost its 5 V, with neither red nor green 5 V led on the A80 board.
I traced the problem to overheating pins in the connector between the transformer and the A99 motherboard (burn marks around the pins).
Wiggling the connector reestablished 5 V, but the overheating is nearly immediate and severe . It does not occur in standby, nor do the connector pins on the A80 board show any overheating when the unit is on. One would expect the current limiter to cut in if there were a short on the bus. The rectifier diodes also get very hot. Evidently troubleshooting cannot last more than a few seconds at a time lest the connector is destroyed.
Questions: (a) is this a known issue, (b) what is the normal current drawn from the 5 V supply, (c) might the rectifier diodes be switching improperly (e.g., causing shorts at switchover), (c) would replacing them by Schottky diodes be indicated?
