On Sat, 05 Jun 2010 10:36:36 -0500, sorry-spammers wrote:

I suppose this is more repair than homebrew, but since at least it's in
the right spirit I hope you'll indulge me...

Took a lightning hit on the power line about a week ago. The ham
antennas were disconnected so the ham gear survived, but some of my
computer & consumer gear wasn't so lucky.

In particular, a Sony XDR-F1HD HD Radio tuner.

It actually works fine. However, there's about 600mV of AC between
ground and the shield sides of the audio output and antenna input jacks.
As you might guess, this leads to a bit of a hum problem!

Suspected leakage across the power transformer (between primary &
secondary) but I'm not finding any with an ohmmeter. There's absolutely
*nothing* on the primary side of the transformer except the power cord
-- no capacitors to ground, nothing like that. Silk-screen on the power
supply board does say there's a fuse *inside* the transformer but
obviously that's not going to be a source of a ground fault.

I'm confident the fault is in the Sony (and not the audio amplifier or a
damaged antenna cable) since if I connect the same audio cables and
antenna to the old analog tuner it works fine.

Anyone have any good ideas where to look?

I guess I could:

- Come up with an isolation transformer & just run it that way. (it
only draws 13 watts) - Build up an external power supply. It only needs
+5.2 and +10.5V unregulated, and the connection points are silk-screened
on the board. - Live with it & just kick in the high-pass filter. (and
use the analog tuner if I want to listen to a program -- the Sony is for
DXing

I would suggest temporally swapping out the xformer with something
comparable or remove the xformer from the radio and see if it has leakage
outside the radio. (assuming it's not a switching supply)