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kenwood th-78a open squelch on vhf side

Discussion in 'General Technical Questions and Answers' started by KV4D, Oct 5, 2009.

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  1. KV4D

    KV4D Ham Member QRZ Page

    i have a kenwood th-78a that has a small problem. the vhf side squelch stays open no matter where the knob is at. the green light stays on and full bars on the meter. there is no sound coming out of the speaker. this is only on the vhf side. i can use the uhf side fine, also can change positions with the 2 and uhf works, vhf wont, right or left side. the vhf will transmit tho. i have searched the internet without finding the problem yet. seen the other common problems but not this one specifically. the c-17 problem usually is on the right side. this problem follows the vhf no matter which side its on.
    thanks in advance
  2. KV4D

    KV4D Ham Member QRZ Page

    anybody have any ideas?
  3. K7MH

    K7MH Ham Member QRZ Page

  4. KB7OSW

    KB7OSW Ham Member QRZ Page

    Repair issues?

    I have had Cliff repair one of my Th78a's in the past. Goog work, at a good price.... Good Luck
  5. N8CPA

    N8CPA Premium Subscriber QRZ Page

    I hope this helps.

    Read page 9. There is a key sequence that changes the function of the tuning knob, which I believe changes the function of the squelch knob as well. IF all else fails, reinitialize the rig.
  6. KV4D

    KV4D Ham Member QRZ Page

    thanks for the ideas guys. still no control tho. it will tx on the left side but the squelch is wide open no matter what i do. factory reset no luck, i done the c17 thing, with no luck either. this must be a problem that is kinda rare cause i have read nothing about it yet.
    i can tx and rx on the right uhf side, tx on the left. no squelch control. i may pull it apart again to see if its the squelch knob??? cold solder joint on the back of the board....maybe??
    thanks again guys
    BTW i noticed its more like it is receiving a signal on vhf, full scale on meter but no noise. it is quiet with no squelch noise. green rx light is on. no signal to receive tho verified by another ht. even with antenna pulled from th-78
    Last edited: Nov 19, 2009
  7. G0IWF

    G0IWF Ham Member

    TH78E squelch problem


    I have a TH78E the european version with exactly the same symptoms that yours has. Mine had been unused for about six years - I took it out of the box and it had no sound on VHF, signal indicating maximum, squelch indicator on and squelch control did nothing. UHF side worked fine. I reinitialized, recharged the battery but still faulty. The next day picked up again tried it and it worked okay!!
    This happened two days ago and so far it is still working well on both bands.
    I'm sorry that I can't offer advice but thought my experience could in some way be useful.

  8. KV4D

    KV4D Ham Member QRZ Page

    LOL.... well at least im not alone...i hope yours stays fixed.
  9. G0IWF

    G0IWF Ham Member

    My TH-78E is not fixed. I've tried it each day since the last post to you and after switch-on it has no sound on vhf, squelch indicator on etc. If I leave it on then after say 10 -20 minutes the sound gradually returns, the indicator goes off and the radio functions correctly. If I leave it on then after about an hour the sound goes off, so does the squelch indicator but the signal bar has gone. If I then switch it off and then back on the radio starts the cycle again with no sound, indicator light on etc.
  10. DL7AHW

    DL7AHW Guest

    Hi dear friend, have you founded a solution for the problems with th78E?

  11. DL7AHW

    DL7AHW Guest

    Same problem

    Hi a friend of me has the same probleme with the th78e. Have you found a solution for it?

  12. KE4EMB

    KE4EMB Ham Member QRZ Page

    Same problem in FL

    I have same problem.
    Found Kenwood Service Bulletin ASB-1013 That lists cause as R97 being "sheard" from control unit board, X53-3420-00 A5. Likely cause was listed as disassembly stress on component. Now if I could only find R97. Another site listed C-17 solder pad failure. Once again cant find C-17.
    Can anyone help with a board layout??? I poked around with a tooth pick and was able to temporarly resolve problem, but couldnt isolate the offending component.
    Thanks, KE4EMB
  13. G0BZB

    G0BZB Ham Member QRZ Page

    Ho Ho..... I am not alone then.

    I took out my pristine TH78E from the drawer where it has lain for ten years and after a week of use as an air band monitor (it seems to have extra rx range) it now has the VHF side squelch light on all the time, a gentle hiss from the audio and it doesn't receive on that channel EXCEPT that if I go down to the airband range below 136MXZ, the light goes out and it behaves perfectly. I think that range is AM not FM. As soon as I turn the VFO knob through 135.995 to 136.000, the bad behaviour comes in again. I can set it to listen on the UHF channel to a VHF frequency and tune the VHF band on rx on that side, but not on the left channel.

    I am very puzzled. If the fault was a component failure, I wouldn't have expected that. I'm wondering if I have inadvertently set it into some strange mode. I can't see small things very well and have fumbled about with the key pad buttons. I could easily have set it into some strange mode, but I tried resetting it and it made no difference.

    I'd really appreciate any solutions anyone can suggest. It seems to be a VERY complicated radio for such a small package. I can't remember half of the key presses to enable features.

    73s de G0BZB.
  14. KV4D

    KV4D Ham Member QRZ Page

    i have gotten rid of mine. i do however have a complete service manual and parts layout for those interested in trying to fix there own. i didnt get mine fixed. but did find out that you can change sides with the vfo. it is related to the left side not the vhf band. you can put the vhf on the right side and it works perfect. (well mine did anyway) so it makes it more useable, just no dual receive but at least i could use vhf again. the left side for some reason is the problem no matter what is there uhf or vhf. anyway email me at kj4dul at yahoo with kenwood 78 manual in subject line and i will email all the info i have gathered on it to you. if i remember correct i have quite a bit of info on them.
    thanks and good luck
  15. KD6WAR

    KD6WAR Ham Member QRZ Page

    I now have the exact same problem with my radio!

    Here is what I found at the Yahoo Groups for the TH-78A:

    Re: No RX on VHF side, always open Squelch...

    --- In, "bushman10980" <bushman10980@...> wrote:
    > Hello.
    > I have a Kenwood TH-78A, is broken - no RX on VHF side and squelch is still
    open. Please help me found a solution.
    > P.S. Sorry for my English.
    This is a common problem for these older HTs. There are 2 capacitors that have
    failed. Look in the files section of this forum and also do a search on the
    messages and you will find out how to repair it. Hope your eyes are better than
    mine. They are almost too small to see well, but the repair is not complicated.

    Ed, WB4RHQ

    I think this is what is known as the "Left-Side Problem" caused by leaking
    electrolytic capacitors C406 and C420.

    I could tell it was a capacitor issue, but did not know which ones.

    Another member of the group posted this:

    "The root cause is the C406 and C420 electrolytic capacitors
    leak which contaminated the surrounding C449 and IC305
    area. It affects the rx backend IC304's limiter
    amplifier voltage threshold level during cold start.
    To fix the problem, I temporary removed the C449 100pF
    cap and bush clean the area with isopropanol around
    the C406, C420, IC305, and C449."
    -JK KC4MPA

    I'll be looking into this in the next few days.

    - KD6WAR
  16. KB8YVC

    KB8YVC Ham Member QRZ Page

  17. YT1PRM

    YT1PRM Ham Member QRZ Page

    squelch th-78e VHF

    Hello, ate some managed to eliminate this problem solved?, To me it pjavilo after long standing in the closet I have not burned or had a battery station oko3 months, when I turned once again as a full scale meter skvelc amount does not open and only on the left side of the VHF gang and a few minutes I'm slowly returns to occur but did not like the FM over we act as AM modulation and here I like this over a year but not to solve the problem and when I put on the right side to be working normally, then VHF and I am as a real FM, I mertio voltage at lijon sumljajuci battery voltage to it and is oko2, 1v which I think is that maybe but I was even changed, if anyone has a solution? thank Milan yt1prm 73:confused:
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