FT-101E Intermittent Audio level/S-Meter level

Discussion in '"Boat Anchor" & Classic Equipment' started by KB3GWQ, Jun 26, 2018.

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  1. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    Months back I got an FT-101e and recapped it and it has been working great the few times I've used it for extended hours (like 6 hours straight a few times!) but now I have this problem where the audio gets cut down a lot and the S-Meter goes down too. I tried wiggling the PL-259 connector, reseating the bulb, moving the band mode, rf gain, rf attenuator switches, cleaning the "Antenna Relay" in the HV cave and even poking around with chopsticks on the modules to wiggle them back and forth and I can't find it. Even tried poking around at the wires around the switches to see if it was some kind of cold joint that is being affected by temperature.

    The problem manifests itself even if the bulb is removed, the antenna relay removed or if there is no antenna attached. When I first suspected the bulb I cleaned it and the socket with de-oxit and it's unrelated to the problem. If I turn on the 25/100khz tune the output is also lowered when the crackling happens. RF Attenuator is working and so are the knobs because even at low volume if I flick the switch or adjust those knobs I can hear small changes.

    When this problem is occurring you can still hear stations it's just the audio and s-meter levels have been knocked down to near S2 or S3 on the meter and the volume to go with it. On 40m where I might have a noise level of S5-S7 when this problem happens (which is now pretty much non-stop even after I left it sit for a day to cool down) it drops down to S0.

    Even with the faint noise you would hear with those things disconnected and the volume at max you can still hear this audio getting much lower and intermittently going back to the original level. It's like as if there is a cold joint but I can't find it and I have no clue where to look. I do have a scope, so if someone can guide the blind here I'd appreciate any help. I'm out of ideas at this point with the basic tests I've performed.
     
  2. N8YX

    N8YX Ham Member QRZ Page

    Look at the 1st RF Amplifier transistor. It's a 3SK40 or similar. Cold solder joint in that area could cause what you're experiencing.
     
  3. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    OK. Which module is that on? And what do I test? I have a DVM but haven't had to get this dirty on fixing electronics besides some generic parts swapping stuff and cleaning switches.
     
  4. N8YX

    N8YX Ham Member QRZ Page

  5. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    Roger, have a SVC manual for it. I see, this is the tiny board that's by the VFO. I will take it out and inspect it.
     
  6. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    OK. So I took the board out and took the transistor out and cleaned the socket with deoxit and also cleaned the card edge on the module. I did notice one of the resistors has the insulation falling off it. When I push on this resistor with a pair of chop sticks that is changing the volume levels. The resistor doesn't look burnt or anything, but I'm guessing if the insulation deteriorates on the resistor than this can affect it? I will replace it anyways but I am curious. Regarding a replacement are metal oxide film resistors OK?
     
  7. N8YX

    N8YX Ham Member QRZ Page

    Metal oxide film resistors should be fine, as long as they don't appear inductive to the circuit and change its tuning characteristics. I doubt you'll have a problem, though.
     
  8. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    OK. Well it's R1 and R3 on the board which according to the parts list is 100K 1/4 Carbon. So I guess metal oxide is OK for this? R3 is the one apparently giving me problems, but R1 also has deteriorated and I think it would be best to just replace both of them. I did disturb VR-1 very slightly and put it back in relatively the same place just to make sure it was not this pot on the board because the back of it is kind of black looking. Hopefully this will not be a serious problem, if so how do I check it and just properly once I have verified it's these two resistors? The block diagram says "Set for minimum signal at 3.840khz when transmitting on 3.800 as heard in separate receiver." This is vague to me, I don't know if this means CW, SSB, or AM. Does this mean I set it to AM and listen on a separate radio listening at 3.840 but the 101e is at 3.800 (or close to it anyways) while transmitting and just the pot until the signal heard at 3.840 on the other rig is as low as I can get it?
     
  9. N8YX

    N8YX Ham Member QRZ Page

    There should be an alignment procedure in the FT-101 Service Manual which covers the setting and the equipment needed to perform the step.

    I imagine Roger will share his knowledge of the '101 series when he checks on this thread...
     
  10. G3YRO

    G3YRO Ham Member QRZ Page

    Hi . . . just seen your post.

    I was going to point out that the Receiver front-end FET is plug-in, so may just need pushing in and out to clean the contacts. (I think Yaesu imagined these might fail due to static etc, so made it plug-in for easy replacement . . . however I have NEVER had to replace one on any FT101 !)

    So did replacing the suspect resistors cure this receiver intermittent fault?

    Regarding adjusting that pot - it just adjusts the Tx Mixer for minimum spurious transmissions - so as it says in the handbook, transmit into a dummy load on 3.800 in the Tune position (set the carrier level so the PA current is about 100mA).

    Then tune into the spurious signal somewhere near 3.840 on another receiver . . . and adjust that pot so the received signal is as weak as possible.

    Roger G3YRO
     

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