"I have a Panasonic 1124 printer which keeps blowing the only 250V 3A fuse on board. The fuse burns as soon as the power is turned on.
I unhooked the components which connect to the logic board - i.e., printhead and tractor feed.
Is it possible that the problem is in the power supply? If it is, what can it be? (The bridge rectifier consists of four hefty diodes)."
(From: Bruce A Haugh (email@example.com).)
With the power supply disconnected from the rest of the printer circuits, blows the fuse, the problem is with the power supply. I have a Raven PR-9101 (made by Panasonic) that has the exact same symptoms. Turns out that one of the secondaries on the power transformer has shorted. You'd need schematics to confirm voltages.
(From: Robert McCallum (firstname.lastname@example.org).)
I've fixed quite a few panasonic printers and yes 90% of the time when the machine is dead, it's one or more of the bridge diodes.
(From: Kerry Messana (email@example.com).)
It's fairly simple to diagnose where the problem is originating. If you unplug (if possible) the output cable from the power supply and it still blows the fuse then the power supply is at fault. As for what could be wrong, well, I am not familiar with the particular supply. If it is a linear supply a good place to start is the bridge circuit. If it is a switching supply you could also start there but there are more possibilities further on.
(From: John A. McCulloch (firstname.lastname@example.org).)
Another very common problem with the whole Panasonic 11XX series of printers is the zener diode and pass transistor. When the diode shorts, the transistor blows, and I mean *blows*!