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Galaxy dx77HML no AM transmit but works on SSB

chassis221

Member
Feb 7, 2011
55
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Philadelphia Burbs
Been awhile since I've been on the Forum but I've been having an issue with my DX 77. Transmits fine on sideband but switch to AM and nothing at all no modulation no power. Same issue with my 95T.
Thanks.
 

Same issue two different radios - I start looking at other things, would be weird for both radios to have the same fault inside. Microphone, meter, system all ok?
 
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I woud start looking the response from Andy at previous thread (he is the master :) ), check that area first. Is it the final stage Collectors being feeded in AM mode?

I have seen several times, some component in that area defective (you can start with the pot for regulating AM power to see if it is not open as it is a weak part).

If all the voltages are present and nothing is working bad in that area, you can review next the carrier oscillator. Is it working and is10.695 Mghz (for AM) present?. Remember that for TX, you need the frecuency from VCO and the one from carrier oscillator being mixed to generate the final 26-27Mghz at output.
 
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Yes I am following Andy's instructions very closely. I was just curious if the op had ever figured out what was wrong with his radio being that I am experiencing the same thing. Didn't mean to get two threads going on the same thing.
No voltage getting to collectors on driver or final in am mode. Am low and high power pots have been tested good. Slight carrier can be heard on monitor radio.
 
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I was headed to Tennessee a few weeks ago and was going to stop by DTB but we passed by too early in the morning and on my way back from Tennessee was a Sunday and I believe they were closed. This thread was very helpful thank you to everyone who give some input.
 
In many instances, the traces can blow from the power switching going on in the front panel.

You'll have to check traces to verify that AM mode is even getting to the AM regulator.

When SSB seems ok, you have your 12~13.8V on the CENTER LEG of the driver and Final - yet it disappears when you switch to AM, it means the AM Regulator is not switching over.

Can be various things including bad or loose wiring in headers from the front panel wiring to the main PCB.
 

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