Recent content by W3FAW

I'm still stuck on this problem. I tried changing out the power transistor Q66 (B754) with no improvement. A discovery I made is that the ground does not go to the chassis. I wonder if that could be part of the problem. I can't tell where the connection is supposed to be made and I don't want...

Hi Rob, thanks for the input. The voltage at that junction is 8.5VDC. I have removed the diodes and the transistors but the bias voltage is still being pulled low through R274, R275 and R276. It is about 0.95VDC on all three. It seems like another component is shorted and pulling down the...

Hi, I have a 2970DX with no output. I'm getting a signal to the driver, but no signal through to the finals or to the linear amp. It is a MOSFET version with bias voltage reading about 0.98VDC on the gates of the driver and finals. The bias should be 3.6 - 3.7VDC. The IRC520's have been replaced...

Hi all, my 2950 has no TX output and I have traced the problem to the driver. I get signal up to the base of the driver but at the collector the signal drops to half power and I get no signal to the bases of the finals. I have replaced the driver with a known good 2SC2166 and have the same exact...

Robb, Old TP3 is now TP7 - No Signal Old D45 is now TP5 - Good signal I'm discouraged by the lack of signal on TP7 and TP17. TP17 is not on the schematic, but it is somewhere at the end of the exciter stage. That looks like real trouble. I can't work on that surface mount stuff. I'm going to...

Sorry Robb. 2950dx was a complete redesign. Here are the best images I can find for both: 2950 2950dx

I'm sorry. I'm mixing you up. In this thread I'm working with a 2950DX. That is way different from a straight 2950.

Robb, One other strange thing is that I cannot see a signal at TP17. It is not shown on the schematic that I can find, but it is somewhere in the transmit section after the mixer but before the driver. It's probably just before the driver. It just doesn't show up on the scope. If the signal...

Well, I have signal at the gate of the driver, but after that I'm not sure what I have. I can tell you what I have, but I'm not sure what it means. The rf signal at the gate of the driver is 300mV. The signal at the middle pin (drain) is 75mV, and the signal at the third pin (source) is very...

It started out with bad TX audio. I checked the TX bias on the mosfet driver and finals. I found that the driver was fine at 3.7 VDC and one final was 2.4VDC and could not be adjusted higher and the other was less than 1VDC and could not be adjusted at all. With a multimeter, I checked the final...

Good for you. But my final bias current is 240mA. Looks like I'll be taking out the finals tomorrow:) I'm betting on one of those MV1Y's. Good Night!

That's great Robb, thanks. I tried it and it works. Now, that begs the question of how to measure the final bias current.

Hi Robb, for a beginner at troubleshooting, you have good ideas. Well, I removed the driver transistor and the MV1Y and found everything to be in order. I didn't remove any other components but I tested for shorts on everything in sight. I couldn't spend much time on it. I've got too many...

Well, I was able to get the final bias current set correctly at 110mA. I found that VR7 (SSB Carrier Balance) was maladjusted. It was set in such a way that it sent carrier signal to the finals during the test. Once I adjusted it correctly, I was able to use VR11 to put it on target. The...

Hi Robb, thanks for all the ideas. I believe in making the "easy" measurements first so I got past the obstacles and measured the base voltage of the driver and two finals. They were well within range of the transistor voltage chart. The finals measured 0.769VDC Which is 0.1 volt above spec...