#bitx40 Q8/Q9 dead - no TX or RX #bitx40


Ryan Flowers
 

Hi everyone, it's been quite a while since I posted here! 

The short version: I have no receive, and Q8/Q9 show now voltage on the base or emitter. Collector has the correct voltage, about 9v. I replaced them (and Q7) with 2n3904's, and the symptom is the same. I checked all resistors in the DDS preamp circuit and none of them were open. I'd think that R92 would be suspect because it biases Q9, but it tests to 10K resistance. C91 and C92 are removed. R91 is fine, as is R80 and R81. So, I'm at a bit of a loss. Here's a refresher on the circuit:



The longer version: It quit transmitting one day, so I took it out of service until I had time to work on it. As I was working on it, receive stopped working. I think my little 5v regulator for the arduino bumped something, and something that might not have been able to get 12v nominal got a dose of 12v nominal. The little power supply lives right above that area on a standoff, but it was floating free while I was working on it. That was a Bad Idea. For now I'd just like to get this thing going again. 

What confuses me is that replacing the transistors didn't do anything to resolve it. I did check capacitors, and some of them showed about 3k-5k resistance, but that was in circuit, so kind of expected. 

If anyone can assist, I'd be grateful for the help to get my beloved BITX back on the air. 

Oh, and as for the dead PA, I think I have that figured out. Guess who didn't have diode protection on Q13? <--- this guy.

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Ryan Flowers - W7RLF
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