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Another PC122XL TX Problem

Discussion in 'General CB Services Discussion' started by Low_Boy, Jul 22, 2018.

  1. Low_Boy

    Low_Boy Well-Known Member

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    The radio receives great. No TX on AM and SSB. No TX light. Not sure it is a PLL problem. I also have no voice output on PA. I do have sound on pa. It seems like when I key the mic. it is not switching. Yes I tried another mic.
    Q24 carrier oscillator is good. D27, 28, 29 Good. Q38 switch is good. X2 removed and tested good but I am showing no frequency at X2 but show 10.6975 at TP3. Q503 is good. And I do not think it is Q36 or Q37 modulation amp because that would not have anything to do with the TX light not coming on. Or would it?

    What have I missed?
    Thanks.


     

  2. Martian

    Martian Active Member

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    TR 31,32, and TR3 form an rx/tx switch.
    How are things looking there?

    pin 15 of the PLL is at what state?
     
  3. Low_Boy

    Low_Boy Well-Known Member

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    All PLL voltages checked out perfect with radio on channel 19.

    Looking at the block diagram my next list of parts to check is Q31, 33,and 19. I will add Q3 to and 32 to the list. I will post my findings.
    Thanks.
     
    #3 Low_Boy, Jul 23, 2018
    Last edited: Jul 23, 2018
  4. Low_Boy

    Low_Boy Well-Known Member

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    Q3 is noise blanker amp
    Would or could that be a problem?
     
  5. Martian

    Martian Active Member

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    I am sorry, that was TR33.
    Typo :(
     
  6. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    The RX/TX switch stuff is behind the ribbon cable the goes to the front panel.

    BUT - PA overrides TX or RX - so you may have more of a wiring or a blown diode.

    PC122TRC465RXTXPLLLOCK.jpg

    Can you tell me the voltage you get on D38 - it should be ON or >5 volts on TX - OFF or less than 1 volt on RX and when in PA mode - again OFF less than 1 volt - with PA on and you keying the mike.

    Thinking bad Q32 or Power steering diode - but D38 can tell me more...
     
    Shadetree Mechanic likes this.
  7. sonoma

    sonoma Sr. Member

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    I have 6 or 7 of the same version radios and every one of them had bad solder joints in them. touch up all the solder joints and all of them started working as they should..
    I have the trc-453 radios trc-465 radios and pc 122 radios and all had bad solder joints and had to look for them with a microscope to see them since some traces are very small. some of the solder pads are not much bigger than the wire that goes though the holes.
    may not be your problem but who knows for sure until you check them out. if it is a bad part you have the right guy helping you now.
     
  8. Low_Boy

    Low_Boy Well-Known Member

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    Andy I got in a bit late tonight so no radio work. I was waiting until all else failed before I checked the parts you mentioned. So I guess I will start at TR32 and check all the hard parts first. I will check the voltages you mentioned.
    Thanks
     
    kaos513 likes this.
  9. Low_Boy

    Low_Boy Well-Known Member

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    quickly before I turn in for the night d38 CB mode .001 volts and the anode and .034 volts on the cathode in PA mode.004 volts on the anode and .030 v on the cathode.
    I'm off to bed thanks
     
  10. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    If you have RX, more than likely the PLL is fine.

    I'm more worried the Mic might be bad...doesn't need any Pin 1 to Pin 4 stuff, just looks at Pin 3 - Speaker is always connected when you disconnect the Mic..D38 applies power when TX is on to mute the Audio Amp - if Q32 was bad, you wouldn't have any RX or TX - but if Q32 is shorted - yes, it's still bad but RX is on even when Q32 is telling it to stay off...TX won't turn on because TR32 can't tell it to (It's a PNP) - D36, D38 and D37 are the Steering diodes in this area D48 is the RX lines, "back emf" protection diode it accomplishes the same (same symptoms) if it shorts.

    The No TX lite is possible TR33 as per Martian - but it requires TR32 to be functioning properly.

    TR31 - RX - 2342, a high gain NPN can be subbed with a 945 if needed..
    TR32 - PLL Lock - 945 NPN...Routes to CB/PA switch, and uses MIC socket Pin 3 - which grounds to pin 1 on TX
    TR33 - TX - 525 PNP - but you can sub a 2SA1015 PNP if needed...

    The 945 and 3242 are the same pinout ECB Leads down facing you, (face towards you leads down) while the 525 is BCE Leads down facing you...2SA1015 IS OPPOSITE OF THE 525 - it's ECB - so it'll have to be installed in reverse - face the other opposite way...

    :+> Andy <+:
     
    Shadetree Mechanic likes this.
  11. Low_Boy

    Low_Boy Well-Known Member

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    I am out the door hopefully I get back early enough to get back on this. I will post findings. I have tried a couple different microphones and also tried shorting the Mic socket to see if it would TX. No luck.
    Thanks
     
  12. kaos513

    kaos513 Well-Known Member

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    I had a smilar issue with same radio was the pa/cb switch was bad
     
  13. Low_Boy

    Low_Boy Well-Known Member

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    Dug in to the hard ones TR31,32 and 33 all good.
    D37 good.
    Next batch will beD48 TR36 and 37.
    D38 is less than 1volt in CB or PA both sides.
     
  14. kaos513

    kaos513 Well-Known Member

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    Check if you have power on the cb/pa switch
     
  15. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    You asked a question earlier - check you TP mirror board jumper to ground - should have volts ALL THE TIME - yes that means it's got power and you can set AM power (carrier) while it's idle in AM mode. I just check it to make sure the AM regulator and Carrier power AM power - can adjust.

    Else - note the length of jumper - when D38 is not working - you may have a blown trace from the rear of the board to the front - it's a PITA but get a magnifying glass and trace the routes and use a DVM to check for continuity.

    I've had 122, 465 and 640e's blow traces - so it's nothing new...

    The transistors need 8 volts from the main regulator to work, so if those traces popped, there's the reason.

    Refer back to the graphic of the three transistors - look for 8 volts along that outer edge trace - that comes straight from the 8 volt regulator. So if the PLL works - you should have power along there.

    The flat ribbon cable supplies power to the front panel - so if it doesn't TX - it means power is not "returning" to the front panel to turn on the TX lite - so that may mean the TX transistor may work, it's not sending power.

    Ok, locate the ribbon cable that goes to the channel selector - with the radios component side up, the channel selectors - RIGHTMOST conductor in that ribbon, is your 8 volts to TX LED. - now what is different here, is you silence the speaker when you TX - so that tells me that TR33 should work but needed to be checked to verify - ok done, but it's not getting from the transistor to the left side, by the PLL and the Channel selector. - again check traces .... VR3 is the TX freq adj, - so I'm thinking a foil trace failure by VR 3.

    So foil side up - locate the outer trace by those three TR33, TR32 and TR31 - and VR 3 - see if power get past VR 3 and towards the first pin of that ribbon connector - this time - it's the first one on the LEFT (Starting from the left)

    :+> Andy <+:

    BREAKING NEWS - Added this in...
    PC122TRC4658VoltSiources.jpg

    :+> Andy <+:
     
    #15 Handy Andy, Jul 25, 2018
    Last edited: Jul 25, 2018

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