On Thu, 2006-05-04 at 03:17 -0400, ARDUJENSKI@aol.com wrote:
> I got a report running the Scout that there was a chirp on the transmission.
> Checking the PS the voltage drops from 14.2 to about 10.3 vdc. I was hoping
> someone could help point me to where to start in troubleshooting the PS.
>
> Thanks
>
>
> Alan KB7MBI
> Woodinville, WA
I'd first suspect output cable connections, especially at the radio.
Tentec and others have had problems. Then the fuse in the output DC
circuit, then one of the pass transistors is likely open and there's not
enough drive for the lone remaining transistor to supply the transmitter
load.
The filter capacitor could be mostly open, and only show hum and low
voltage on transmit. Hum from a power supply is dependent on load. It
takes very little filter capacitor for no load, but lots for the big
load.
If you check the voltage across the filter capacitor unloaded and loaded
you will see a significant voltage change. If the loaded voltage gets
under 15 or 16 volts that filter capacitor or a rectifier problem could
be major contributors to low output voltage under load. Hook a paper
capacitor in series with the voltmeter AC probe and see how much the
ripple rises under load. It ought to stay under half a volt or so.
And it could be as simple as poor connections in the heavy current
sections.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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