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KV4D
10-05-2009, 05:23 AM
hello,
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
KV4D

KV4D
10-09-2009, 04:06 AM
anybody have any ideas?

K7MH
10-09-2009, 06:01 AM
Check with these guys and see what they know about it.
http://groups.yahoo.com/group/th78a/

KB7OSW
10-31-2009, 07:03 AM
I have had Cliff repair one of my Th78a's in the past. Goog work, at a good price....http://www.avvid.com/ Good Luck

N8CPA
10-31-2009, 11:04 AM
I hope this helps.
http://www.radioamateur.eu/schemi/TH78_user.pdf

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.

KV4D
11-19-2009, 02:10 AM
I hope this helps.
http://www.radioamateur.eu/schemi/TH78_user.pdf

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.

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
troy
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
thanks
KV4D

G0IWF
11-24-2009, 08:02 PM
KV4D

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.

G0IWF

KV4D
11-27-2009, 04:46 AM
KV4D

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.

G0IWF

LOL.... well at least im not alone...i hope yours stays fixed.
troy
KV4D

G0IWF
11-28-2009, 04:28 PM
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.
G0IWF

DL7AHW
03-10-2010, 03:02 PM
hello,
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
KV4D

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

dl7ahw

DL7AHW
03-10-2010, 03:05 PM
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.
G0IWF

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

dl7ahw

KE4EMB
03-21-2010, 09:11 PM
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

G0BZB
05-11-2010, 07:14 AM
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.

KV4D
06-11-2010, 01:04 PM
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
troy
KV4D

KD6WAR
07-22-2010, 03:43 AM
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 th78a@yahoogroups.com, "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

KB8YVC
07-27-2010, 04:40 PM
Here's a link to the PCB layout of the TH-78a

http://www.radioamateur.eu/schemi/TH78_pcb_KE4DRN.pdf

YT1PRM
08-04-2010, 12:52 PM
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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