1960's psu....smoking 1N4005

Here is a small 12v psu board from a Wayne Kerr B522 Component Bridge.....(new to my lab, and arrived in unknown working condition)

I cannot figure out why this (brand new) 1n4005 rectifier immediately gets hot and smokes. (transformer also gets hotttt.)
The old ones there had also fried, so I replaced them.

This is British gear, and has a mains selector switch for 105v or 240v...so I chose 105v and used a variac.
There is a single 0v centertap on the xformer secondary, with a wire to it, but it does not go to the PSU board.
The diode gets smokey hot whether this psu board is loaded or unloaded (@ the 12v outputs).
I replaced all components on this board with new parts.
The diode to it's left, also gets hot.....but not as fast as the one noted (about 5 seconds).

any ideas ??

Thanks,
FB

Freq Band said:

There is a single 0v centertap on the xformer secondary, with a wire to it, but it does not go to the PSU board.

Click to expand...

Where does it go?

Peace,
Paul

Yea,

Trace that out- sounds like the "0V" on your picture above is connecting to that centre tap on the transformer somewhere accidentally. Is there a PCB touching ground, or have you screwed a screw too far into the case and its touching a board?

Mark

OK, I'll trace that wire.....maybe I'll unsolder it, and see if the diode stops getting hot.....
You know gear like this.....spaghetti wired inside.


=FB=