Icom IC-271a needs help

Discussion in 'Radio Circuits, Repair & Performance' started by N2OG, Mar 31, 2017.

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  1. N2OG

    N2OG Ham Member QRZ Page

    Radio works good on FM tx and rx, and ssb rx is good, But ssb tx I'm told on air is scratchy and or raspy audio, would the trimmers in pll be causing the problem?, or maybe a electrolytic cap. Was told it had been re capped but it does not show it.
     
  2. G4COE

    G4COE Ham Member QRZ Page

    Don't go tweakin' nuffin until you know what the fault is.... I wouldn't go casting evil eyes on the PLL just yet, what about the SSB carrier crystals? Trimmer capacitors is indeed a common fault with ageing equipment with ageing it is not surprising to find tarnished trimmers causing aggro.

    Best plan is to grab a service manual freely available, then check the SSB carrier generator with a 'decent' frequency counter and check as described in the manual.

    Here is a starter-: Have a look here http://www.qsl.net/icom/oldicomfaq/ic-271a_h.html
    and for the service manual https://www.manualslib.com/manual/1003206/Icom-Ic-271a.html
    Click the download button, I'm not a robot and then click the pictures and the manual can be downloaded in pdf format.

    Dave
     
  3. WB8NQW

    WB8NQW Ham Member QRZ Page

    Mike gain too high in ssb mode?
     
  4. N2OG

    N2OG Ham Member QRZ Page

    No that is not it, tried that already, Icom is telling me to change the two trimmers on HPL along with a 100uf 16v capacitor, and a new alignment, and this has not had a recap done to it, So, the recap will be done along with the trimmers, and they should arrive this week.This may turn out to be a long drawn out job, 100 plus caps to change.
     
  5. N2OG

    N2OG Ham Member QRZ Page

    Well, trimmers have been replaced in the HPL, and realigned and SSB audio output still just as raspy and rough as before, even tried another mic, thinking the sm-6 was the culprit but not the case.
     
  6. AA7QQ

    AA7QQ Ham Member QRZ Page

    Download the service manual & do a full alignment with the proper test equipment. Or, have someone else do it. I have the X51 series & fully aligned them. THey work great. The 451 was way out of alignment.

    Ed
     
  7. W1VT

    W1VT Ham Member QRZ Page

    How does the CW carrier sound? If the problem is in the PLL, the CW should sound bad. If the CW note is nice and clean, it isn't the PLL circuitry. You may also be able to listen to different oscillators with a wideband receiver to see which ones are bad, but you have to be careful, as the bad note may belong to the receiver! This is a good place to use an HP8640 as the LO for a direct conversion receiver.

    Zack W1VT
     
  8. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I agree about trying CW, full-power, key down, and listening on a second receiver to see how clean the note sounds.

    If it's pure and clean, I'd really doubt the problem has anything to do with the PLL, trimmers, or anything associate with that.

    If it sounds "buzzy," I'd check the internal power supply in the 271A to be sure it's regulating properly. That's something that can affect how SSB modulation sounds, how clean the CW note is and several other things re the transmitter and not impact the receiver at all.
     
  9. N2OG

    N2OG Ham Member QRZ Page

    Radio is going to Scott at MTS for repair, he has all the equipment to make any repairs needed, best to have him do the job.
     

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