[ICOM] IC-756PRO2 tx audio issue

[Eric Dobrowansky K2WD]

	Good Afternoon, I have an IC-756PRO2 which is experiencing audio problems on SSB. The radio will work fine at times. Then, all of a sudden, the transmit audio will go into distortion, getting worse the longer I transmit. RF feedback external to the rig has been ruled out. The power supply and dc power cable have also been ruled out. Same for the antenna. I have tried multiple supplies and cords. Same on a dummy load or antenna. The radio is being run into an IFR COM120B (internal dummy load), and monitored on another HF receiver. The test is performed by using one of the recorded TX msg memories. The msg recording itself is crystal clear, and sounds clear in the radio's monitor function even when the tx distortion issue is present. This also rules out a microphone issue. The problem also occurs no matter what power level the rig is set to, and occurs the same whether the pwr control is set for 10w or 100w. If I repeatedly play the recorded message, it will sound crystal clear at first, then slowly get to the point where it sounds like a poorly driven or biased solid state transistor amplifier (remember how those cb linears sound on ssb?). The problem will dissappear for a day, then come back for a day. Then return again at a later time. Very fustrating! I am guessing something is beginning to fail on the PA module. Once in a while, if I key the rig in CW or RTTY, I will see the power output fluctuate down from 100w to around 90w, then back to 100w. Anyone see such behavior before? Eric K2CB 	Good Afternoon, I have an IC-756PRO2 which is experiencing audio problems on SSB. The radio will work fine at times. Then, all of a sudden, the transmit audio will go into distortion, getting worse the longer I transmit. RF feedback external to the rig has been ruled out. The power supply and dc power cable have also been ruled out. Same for the antenna. I have tried multiple supplies and cords. Same on a dummy load or antenna. The radio is being run into an IFR COM120B (internal dummy load), and monitored on another HF receiver. The test is performed by using one of the recorded TX msg memories. The msg recording itself is crystal clear, and sounds clear in the radio's monitor function even when the tx distortion issue is present. This also rules out a microphone issue. The problem also occurs no matter what power level the rig is set to, and occurs the same whether the pwr control is set for 10w or 100w. If I repeatedly play the recorded message, it will sound crystal clear at first, then slowly get to the point where it sounds like a poorly driven or biased solid state transistor amplifier (remember how those cb linears sound on ssb?). The problem will dissappear for a day, then come back for a day. Then return again at a later time. Very fustrating! I am guessing something is beginning to fail on the PA module. Once in a while, if I key the rig in CW or RTTY, I will see the power output fluctuate down from 100w to around 90w, then back to 100w. Anyone see such behavior before? Eric K2CB 
Good Afternoon, 

I have an IC-756PRO2 which is experiencing audio problems on SSB. The radio 
will work fine at times. Then, all of a sudden, the transmit audio will go into 
distortion, getting worse the longer I transmit. 

RF feedback external to the rig has been ruled out. The power supply and dc 
power cable have also been ruled out. Same for the antenna. I have tried 
multiple supplies and cords. Same on a dummy load or antenna. 

The radio is being run into an IFR COM120B (internal dummy load), and monitored 
on another HF receiver. 

The test is performed by using one of the recorded TX msg memories. The msg 
recording itself is crystal clear, and sounds clear in the radio's monitor 
function even when the tx distortion issue is present. This also rules out a 
microphone issue. 

The problem also occurs no matter what power level the rig is set to, and occurs 
the same whether the pwr control is set for 10w or 100w. 

If I repeatedly play the recorded message, it will sound crystal clear at first, 
then slowly get to the point where it sounds like a poorly driven or biased 
solid state transistor amplifier (remember how those cb linears sound on ssb?). 

The problem will dissappear for a day, then come back for a day. Then return 
again at a later time. Very frustrating! 

I am guessing something is beginning to fail on the PA module. Once in a while, 
if I key the rig in CW or RTTY, I will see the power output fluctuate down from 
100w to around 90w, then back to 100w. 

Anyone see such behavior before? 

Eric 
K2CB