My MLA-2500 amp blew the leg off one of the diodes on the diode board after
a wire was left too close to the leg ( I think the wire ultimately went to
the 12.6v secondary winding on the transformer, I will have to verify that.
The insulation was kinda wrinkly and the wire was of course parted at the
short). After the diode ad wire were replaced the amp blows the fuse when
switched on, sounds like a big arc somewhere. The tubes were pulled and the
amp still blows the fuse. (No shorts measured on the tubes)
I have turned all the lights off in the shack both covers off and switched
the power on the amp (and blew a few fuses) trying to locate the arc. No
luck seeing an arc and my eyes are ok... ;-)
Next I floated all of the secondary winding on the transformer. 120v, 800v,
6.3v and a 12.6v. Flipped the power switch and the amp does not blow the
fuse. With the power off I checked continuity between each secondary line
and ground and for shorts between all secondary windings to each other.
A problem exists on the 12.6 winding. Measuring the voltage with an RMS volt
meter I get around 177v or 167 or so volts between each of the 12.6v leg and
ground. I get no voltage when measuring between each leg of the 12.6 legs.
I don't understand why the voltage is so high because I show no conductivity
between the 12.6 winding and any other leg on the primary or secondary of
the trany.
Scratching head.....
Ken
N4zed
http://www.qrz.com/db/N4ZED
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