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Tram D201A No carrier, am modulation good

T

troyota

W9WDX Amateur Radio Club Member
May 9, 2007
125
9
28
Well here we go again. After the SSB receive is finally working for a day or 2. Now I have lost the AM carrier. However, it will still modulate 20 watts. I have 0 power/modulation on LSB or USB. Before this happened AM transmit worked good. I had a 5 watt carrier on am and 20 watts modulation. I only had about 5 watts modulation on SSB. I have tried another BA and BM board with no luck. I have noticed the last few days the noise floor was really quiet, but would still pull out the weak receive signals. I checked with my Yaesu 990 and sure enough it would hear the signal but had quite a bit of normal white noise. Turn the switch to the D201a, no white noise but the signals were still coming in. Anyway, not a real issue I just thought it may be related? Oh, BTW the receive has not been affected with the vacation of transmit. (for now anyway)
Thanks
 

Should be several bias resistors, check those to see if they are still somewhat close to the values they should be.
 
Thanks Wavrider and Nomad, I checked the resistors and did find R711 out of spec. 1/2 watt 330ohm had changed to 6 ohm. I replaced it but didn't get any change yet. I do have the complete service manual and schematic. I would have never gotten this far without it. I admit, I struggle with the schematics sometimes.
I did have to change out c706 on this one due to it being jackhammered and broken. Luckily I had a replacement from a donor. I used the By Gosh By Gum method and the neutralization went fine. No oscillation on SSB, transmit was on frequency. I'm thinking were good. BUT, I did not set the bias then. For some reason I got mixed up and was thinking I don't have to do that, this one is fixed bias..... (Yes, I'm a dummy)
Now, back to where we are...bias on AM RX was -24.5, adjusted to -40. SSB RX bias was -46 and will not set any lower, the trimmer is on the stop. I try to peak t700 for max -dc volts on channel 20 TX and nothing, no change at all. Because they interact with one another, I see if c706 will make a difference and it does not. T700 and C706 makes no change no matter where they are set. Readings were taken in crystal mode.
Thanks
 
I finally got a very minimal carrier. I tried to neutralize, tune and load with no luck. Then I noticed my frequency counter was reading output, unfortunately it was transmitting at 25-26mhz. I started checking things and then verified the fact that I am indeed a dumass. What I thought was R711 a 330 ohm that was reading 6 ohm was actually R712 a 4.7 ohm. I changed it back to the correct value. Went through the alignment again and all went well, reset ALC and AMC. However I am skeptical on the fix, because I changed that resistor to the wrong one after I had the no carrier issue. But for now I have this thing pretty close. AM and SSB receive is good, except for the low noise floor in AM. I am pretty sure it is the RF gain control pot. It feels rough and gritty while I turn it. Transmit appears to be ok. AM carrier about 5w swings to 20. SSB modulation to 30 watts. I have been getting superb audio reports. Crystal clear broadcast audio is what I am told.
Thanks guys for all the help, hopefully I can call this one good and start on another one.
 
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