On Sat, 2009-11-07 at 05:32 -0800, George Stern wrote:
> Hello,
>
> I have a 962 Power Supply Im using with my Omni 6+. I recently had the
> rectifier fail in it. I replaced the rectifier, pass transistors and all
> filter caps in the unit.
> The supply operates fine however I noticed yesterday when I accidentally
> keyed the rig into a high SWR the supply didn't trip and shut down.
>
High SWR does not automatically mean high supply current. It only means
high supply current when that high SWR presents a LOW load impedance to
the PA transistors. And that impedance is affected by SWR and the
transformation of the output low pass filter and the PA output matching
transformer. A high SWR can easily show a high load impedance at the PA
while showing a low impedance at the coax connector due to that output
filter and that will lead to a lowered supply current, but raised
collector voltage on the transistors. Fortunately TenTec chose rugged PA
transistors to accommodate such a situation.
A high SWR can show any kind of impedance at the transistor collectors
from very low to very high with all possible magnitudes and phase angles
in between. Its only the low impedance occasions that make the power
supply current protection function.
> I was under the impression the supply has a circuit breaker, however reading
> through the description the supply has an electronic current limiter with a
> factory set threshold of 22 amps.
>
> My question is since I've replaced major components of the supply and likely
> affected the overcurrent trip settings how do I adjust the electronic current
> limiting to the proper value?
>
Replacing those parts should not have affected the overcurrent trip
point.
> I have 2 pots in the supply R24 100 OHM which is off the B+ rail and goes
> through a resistor to to pass transistor Q8 and R30 1K which is between the
> B+ and B- rail and the wiper going to the small IC which I assume is the
> regulator.
>
Without seeing the circuit, I'd say I don't know what R24 does but the
other pot, R30, probably sets the supply voltage. They don't need
adjustment.
> If someone has done this before or has any info on the adjustment procedure
> any information would be greatly appreciated.
>
> 73,
> George K2JYL
>
73, Jerry, K0CQ
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