[TenTec] Omni C + new Ham = Oops.

[Mike Bryce]

excellent troubleshooting

although the diodes on the swr board don't control the PA in anyway.

but it could be that a spike came down the coax and took a few things out. It's possible.

if you can get to the base of the transistors in the PA, in the lock posistion position and the drive all the way down, you should see supply voltage on the collectors, zero on the emitter and .7 on the bases.

since the base resistors are toasty, be sure you replace them with like units, carbon flim or metal film and not wirewound.

call RF parts and see what they have in stock. I'm not much for matched pair in simple PA designs like the ones in the Omni, so save some money

mike

Mike, WB8VGE
SunLight Energy Systems
The Heathkit Shop
http://www.theheathkitshop.com/
J e e p
o|||||||o 

A man with one clock knows what time it is. A man with two clocks is never sure. 



On Oct 15, 2013, at 12:23 PM, Paul Harker wrote:

> Well... here is where I'm at:
> 
> Checked the 914 diodes on the SWR board and sensing diode (D1) was bad
> (leaky reverse biased). A big smile.
> 
> I replaced the offending diode, put everything back together, attached a
> dummy load to the output and turned up drive to see how much current was
> drawn. I noted a 3 amps input power increase, and smoke. Smile goes away.
> 
> Tearing it back down I discover 3.3 ohm R5 and R8 have acquired deep tans.
> These couple the impedance matching transformer to the bases of the power
> transistors. A subsequent check verifies proper bias voltage to the final
> stage.
> 
> Though toasty brown, and slated for replacement, R5 and R8 are still
> correct values.
> 
> Unless I'm missing something major (always a possibility) I'm thinking that
> this kinda seals the deal on the power transistors being bad.
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