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Realistic trc 458 no receive no transmitt help

Discussion in 'General CB Services Discussion' started by drking, Apr 19, 2017.

  1. Robb

    Robb
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    Yup

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    Well, tantalums aren't subject to drying out like electrolytics are - which is their failure point - as we know. From what info I've gathered, they can fail from moisture intrusion or by being accidentally shorted. Then their life expectancy drops off rapidly. However, the last radio recently repaired was a Uniden PC 244, it had a failed tantalum at the audio chip. When I've rebuilt some old 148's, a couple of them had tantalums that were far out of spec, so they were replaced. Not sure of their life expectancy overall.

    Make it an option with your kits and then see how it goes from there?
    The BAT85's in the last kit you sent was a real useful item! Their forward/turn-on voltage is lower than the STMicros. Good stuff!


     
    #16 Robb, Apr 20, 2017
    Last edited: Apr 21, 2017

  2. drking

    drking
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    Well it seem like I have distroyed the radio the ribbon connector is rotten just broke up as was cleaning wonder if I get that socket to buy old or new
     
  3. Robb

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    I wouldn't say that you have ruined it, but you may have made it a little harder to fix. You have to give that cable a delicate touch when cleaning it.

    Some guys have used old floppy disc drive computer cables to roll their own cable replacement by hard wiring one cable end to the board and then building up a perfboard for the ch LED/channel selector board for the other end. Might still be able to find it on YouTube if you dig enough. But that is also a little harder to do and takes some finesse.
     
    #18 Robb, Apr 20, 2017
    Last edited: Apr 21, 2017
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  4. drking

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    It's not the cable it's the connector on the board I want to change it as it is dry rotten
     
  5. LeapFrog

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    It might be easier to go ahead and get one from a parts radio that is in better shape, or you might consider removing the factory ribbon cable and use an old computer hard drive ribbon cable, each point wired in and soldered individually or maybe there is room to put pin headers on one end to make it simpler, but I don't know if the radio's PC board will have a standard pin spacing.

    (I've never had the chance to look at one of these TRCs in person)

    My point is that the cable socket will likely be proprietary and a modern replacement will probably be hard to find, but I hope I am wrong and that they are available somewhere. Best Regards
    -LeapFrog
     
  6. Robb

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    Might need to find the same radio in non- working condition and use it as a parts radio That is what I did, as this made it much easier to make one good complete radio.
     
  7. sonoma

    sonoma
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    I have 3 presiden washington 858 pll radios I rebuilt a couple years ago and one the socket was bad in also. what I did was removed the socket and soldered the ribbon cable to the main board. the ribbon on this one was long enough to reach the solder locations. the radio is still working that way. may be a option on yours also if you are careful with it.
     
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  8. drking

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    Ok Robb now I wired back the selector ran wire from the board to the selector 1 wire at time an still no display no ash noise either
     
  9. Robb

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    Might want to re-check your work.
    No continuity = no ch LED display/receive/transmit/channel selection.
    Either that, or the PLL chip is toast, or voltage isn't getting there.
     
  10. drking

    drking
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    So if the chip is fried will that cause no led display
     
  11. Robb

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    pll.PNG

    Or no voltage getting to the PLL or to the cable. That PLL is getting rare. Check to see if it has had a channel mod hack and that all solder joints are good.

    You can see from the schematic pic here that the entire feed thru that cable to the ch selector/LED comes from the PLL chip.

    Check your voltage feed and ground to the PLL and ch selector/LED too.

    http://www.cbtricks.com/radios/cobra/139xlr/graphics/cobra139xlr_sch.pdf
     
    #26 Robb, Apr 24, 2017
    Last edited: Apr 24, 2017

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