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TS-930 little to no output in AM mode  

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aj6id
(@aj6id)
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I bought this radio a few months back and after getting a little familiar with it, (my first HF radio) I've realized that the AM mode is not working correctly.

I easily get 110 watts in CW, 55 watts in Tune, and I get swings of 80+ on SSB, so I'm assuming the finals are good.

Symptoms: If I max out the CAR on AM I only get 1-8 watts for a carrier (depending on the frequency I'm tuned to. If I put an audio signal into the radio I can get the power up to 10-20 watts at the modulation peaks. The AM reception is great, so the problem has to be somewhere in the AM TX circuit.

Observations: Only in AM, I do not see any ALC movement. I also don't hear my voice when the MONI is engaged (like on SSB). I don't know if it's supposed to work the same as SSB. Can someone confirm that? Power is measured into a dummy load (Bird 82A) and the power levels I observe agree between the internal meter of the radio, as well as a new external power/SWR meter.

This radio is a later-production model (s/n: 508xxxx). When I compare mine to the service manual schematics, I see a lot of discrepancies from the post s/n: 310xxxx schematic; but it does look the closest of the 2-generations shown; compared to mine.  

I heard these radios are notorious for bad solder joints so I desoldered and resoldered every connection on the RF board, but it did not improve anything.

Anyone else ever had this problem?

Any ideas of where to poke-at next?

Thanks.

AJ6ID (Nick)

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Posted : 31/05/2019 10:06 pm
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