G'day Ken.
It has to be the transformer. It is only when you connect the
rectifier/filter assembly that the fault occurs because that is somehow
providing a return path to the faulty burnt through windings.
I have a transformer removed from a friend's Alpha 91B amplifier here
that caused similar symptoms. Run it by itself and everything runs
sweet. Connect everything up and all hell breaks loose. Apparently that
was a common problem with that amplifier.
It is insulation breakdown or burn through between windings in your
transformer. Disconnect everything from the transformer and check with a
megger, every wire to every other wire.
Good luck, Alek VK6APK.
On 7/06/2025 4:55 am, Ken Claerbout wrote:
I've been trying to repair a Ten Tec Titan Model 425 amp and I'm about out
of ideas. Here's where I'm at.
The Soft Start 1.5 amp fuse blows.
This model power supply has the separate rectifier and filter board,
mounted on top. The soft-start and bias circuitry are on the lower board.
With the rectifier/filter board disconnected, the fuse does not blow. I
have the gray cable connected between the PS and RF deck but not the HV
cable. Anytime I connect the rectifier/filter board the soft start fuse
blows instantly. Seems simple enough. Most likely something on that
board, bad cap, diode, the usual suspects. Nope! Everything checked OK.
But NR4M had new caps from a project he did so I "borrowed" eight of those
and replaced the caps. Still blows. Replaced diodes and resistors. Same
thing, fuse blows. Everything on the board has been replaced at
this point. I don't see any burned traces on the board, like what happens
sometimes.
I pulled the lower board and looked it over. I don't see anything wrong
with it either. I don't see any DC shorts on the transformer. I've had a
few of those go bad in the past. They take out the 20 amp line fueses and
I can measure the short. So to recap
1. The soft start fuse is blowing
2. It doesn't blow with the rectifier/filter board disconnected
3. All components have been replaced on the rectifier/filter board.
What am I missing??
73
Ken K4ZW
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|