Yaseu FT-101e RX audio issue...Help

Discussion in 'General Technical Questions and Answers' started by N8PWM, Aug 4, 2016.

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  1. N8PWM

    N8PWM XML Subscriber QRZ Page

    my Ft-101e has developed a strange rx issue. When powered on rx audio is fine then it quickly fades to distorted low volume and then gone completely. I turn the rig off and then back on and the same happens. Almost like a cap going bad as it charges. The 1315 af board appears to have been recapped at one point. I can't figure it out short of recapping the board with known good caps. Am I looking in the wrong place? Any help would be greatly appreciated.

    Also I lost all tx audio just before the rx issue started. This is kind of pointing me to the af board.

    Thanks,

    N8PWM. Craig
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Assume you have the service manual.

    Pages 4-13 and 4-14 have a "fault tree" which is very helpful in isolating problems; page 4-17 has a voltage chart.

    I'd start there, and check all the operating voltages per the voltage chart on p. 4-17 using a good quality VTVM or DVM. You're likely to see something that doesn't read per the chart and that will be a strong tipoff to the location of the fault.
     
  3. N8PWM

    N8PWM XML Subscriber QRZ Page

    I had a look at the chart but the locations don't make much sense. I pulled the AF board and found many bad electrolytic caps and also several split open Mylar caps. I have replaced all but 6 of the electrolytic caps and all the split Mylar caps. Still same issue. I am still suspest of the board. That is also where the troubleshooting chart led me. The audio is great on power up but fades to nothing as before. I am stumped. Can you point me in the direction of how to find the points on the voltage chart? Maybe it's a bad cap on the regulator board.
     
  4. WA7DU

    WA7DU Ham Member QRZ Page

    Sounds (ignore pun) like a golden opportunity to use an audio signal tracer. You wouldn't happen to have an audio amplifier just laying around with no purpose would you ?

    I am unconvinced that the problem is related to a capacitor charging, then causing the fault. Enen though you did not disclose how long between good audio and bad audio, I doubt that there is a time constant in any circuit in the radio long enough for you to hear it go from good to bad. I'm more inclined to think that it could be related to something going from cool to hot--in other words, the fault may be temperature dependent. You might try some freeze spray on the audio board. You might also gently "thump" the board with the eraser end of a pencil to see if vibration or mechanical shock (gently applied) might reveal aa broken solder joint or a bad connector.

    BTW, what do you mean when you write that the voltage chart locations don't make sense--can you provide an example ?
     
  5. N8PWM

    N8PWM XML Subscriber QRZ Page

    Well, when I look at the voltage chart, it has MJ and Pin numbers and I am confused on these locations. I assume that they are pin locations on specific boards but thats as far as I get. The schematic is not very clear when blown up.
    Unfortunately I do not have an audio signal tracer. Had one years ago but was forced to clean out the shack.
    As far as time between the failure of the audio, it takes all of about 15 seconds. Starts out great and then distorts and fades away to nothing. I did find that many of the caps on the AF board were bad. I have replace them and the initial audio I get is 100% better before it disappears.
     
  6. N8PWM

    N8PWM XML Subscriber QRZ Page

    More information. Since this is my first Yaesu, I have been doing some research on issues with this unit. In poking around I found a post about the voltages on the rectifier board being too high. In this persons case, it appears that the coupling capacitor, C13, between the 12BY7A and the finals
    was bad, causing the -100 to hit -160. All other of his voltages on the rectifier board were fine. I am going to check this out, but I suspect that there are other issues here that I am still not seeing.

    Another point that I forgot to post. I had initially noticed that the mic audio had completely failed. I tested my mic and its fine. I was also able to make a good CW contact even thought the mic audio was gone. Shortly following that contact, the RX audio started having issues.

    These are the readings that I took on the rectifier board with all other boards installed and the radio idling with receive audio failed. Heaters off.

    Voltage Spec Measured Voltage
    -100 -176
    +160 +177.5
    +600 +727
    10.5AC 11.41
    +13.5 14.43
    10.5AC 11.38

    The same readings were taken with the heaters on.

    Voltage Spec Measured Voltage
    -100 -172
    +160 +173.1
    +600 +705
    10.5AC 11.07
    +13.5 14.03
    10.5AC 11.20
     
  7. N8PWM

    N8PWM XML Subscriber QRZ Page

    More information. RF output has been fine. All reports from QSO's have said that the signal was clean and strong.
     
  8. N8PWM

    N8PWM XML Subscriber QRZ Page

    OK so I recapped the regulator board and I also found a trace that was cut. No idea why but it was a ground trace...fixed. No change however it did need it new caps as some were starting to push out the bottom.

    I checked the TX and it is still working fine on CW but no audio with a mic.

    I did not notice this before but the RX audio comes back for about 5 seconds and then fades away again when I switch the MOX on and off when tuning up. I cleaned the relay thinking that might be it but no luck.
     
  9. N8PWM

    N8PWM XML Subscriber QRZ Page

  10. WR2E

    WR2E Ham Member QRZ Page

    Did it appear intentional?

    Did you follow the schematic to see if you could determine where in the circuit?

    I would be investigating this first. Seems WAY off.
     

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