[Milsurplus] PP-109 PSU Parts Needed

[W7QHO at aol.com]

In a message dated 1/12/07 3:08:36 PM, Jim.Falls at conservation.ca.gov writes:


> This is the 12V one that drives my RT-68/GRC. It has a dead vibrator and I 
> am out of 5A fuses. Vibrator hums happily but is shorted inside. Causes an 
> overload in the 85V Primary circuit, makes R-19 get HOT and blows the fuse in 
> about 10-15 sec.
> 

Jim,   

Let's see, 7 pin synchronous vibrator, could be either series or shunt type, 
looks like the same type used in the DY-88.   Vibrator apparently running but 
series resistor to the primary CT heating up and fuse blowing.

Internal short in vibrator suspected.   If shunt type vibrator, pin 6 would 
have to be shorted to pin 7 (or to the case) to give observed symptoms.   If 
pin 1 (other side of primary) were shorted to ground (i.e., pin 7 or the case) 
vibrator would not be running.   If series type, either pin 1 or 6 grounded 
could give the symptoms observed.   What do you find when applying an ohmmeter to 
the vibrator pins with the unit pulled out of the PP-109?   Pins 5 and 2?

Note that C-20 shorted could give same symptoms.   If this is the case, fuse 
would blow even with the vibrator removed.

Short in the primary could also give same symptoms.   Hard short in the 
secondary circuit could too.   Ditto a shorted buffer cap (C-23).

Any output from the +85 volt supply in the short interval before the fuse 
blows?

Does swapping one of the other vibrators into the 85 volt circuit solve the 
problem?

Not uncommon to have to open up these old vibrators up and clean the 
contacts.   May take a lot of sanding, the crud is very hard (whatever it is).

Dennis D. W7QHO
Glendale, CA
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