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959 has low modulation

Jdb0367

Jdb0367

Member
Apr 8, 2016
31
6
18
57
Mifflintown, PA
I was hoping for a bit of help here guys.
I have a 959 that has very low audio and modulation.
Low and high carrier settings adjust fine from 1-10 watts.
I have replace the driver, and both finals, and checked voltages across the board. Watching it on the scope while turning vr16 shows very little change.
Injecting the 30mv, 1KHz singnal while on SSB causes some very erratic movement on the radios output meter as well as with the mod signal on the scope. However if I turn my fine adjustment up on my generator, this seems to steady out.
PA seems to be putting out but RX and TX are just very weak.
I'm leaning towards IC9 but at this point, I'm just not sure. Been working on this thing for a few days now and could really use some advice.
Thank you for any and all replies.
 

Robb said:
Has the AM Limiter been removed?
How well does the PA function work?
Did you try replacing the AM Modulator?
Click to expand...
The AM limiter was not removed and yes I did replace it even though it showed good with the voltage checks.
I have made progress since I first posted. Going back thru the alignment again, I noticed L40 was strange.... as in, when adjusting it, the wattmeter and the scope would jump as if the pot was shorted. Searching the board, I found a couple of solder balls and a few heaping piles (factory solder) that were leaning and probably touching some other joints. I cleaned the board up and continued with the alignment and WA LA! Well almost.
I now have modulation that is adjustable. Audio thru the talkback and my sig gen comes thru on receive. The audio still doesn't seem to be as loud as I feel it should be, but I think I need to get away from this thing for awhile.
This is a new radio and it's the Vietnam version. The board looks really crappy compared to the one I have that's a few years older and from China.
Thanks for the reply Robb. I've been scouring thru the forums here for a few weeks and there seems to be a wealth of knowledgeable people here! Yourself included.
 
Thanks for the compliment, but I am just a hobbyist that also owes this forum for the help that I've gotten over the years. I too work on radios as a hobby; don't make a dime. Have worked on my share of 959's - tho. Got a lot of help from here on the WWDX.
 
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Robb said:
Thanks for the compliment, but I am just a hobbyist that also owes this forum for the help that I've gotten over the years. I too work on radios as a hobby; don't make a dime. Have worked on my share of 959's - tho. Got a lot of help from here on the WWDX.
Click to expand...
Yeah....I made a mistake when I decided to open my first radio. Lol
I'm an auto mechanic by trade and that has led me to being a major perfectionist. If it looks like it has room for improvement, I must try to do it.
Now I have one more hobby to add to the seemingly million other ones. Have a great day and enjoy the weekend!
 
Ok guys. Here's what's up with this demon 959 now.
After going over every inch of the board till I was cross eyed, and replacing L40, I realigned and have this thing screaming 60 watts with outstanding audio.
Modulation running 90% and I can adjust dead key to 4 on low and 15 on high.
Transmit audio is crystal clear and very loud!
Time to throw the covers on, wipe of the prints and take it to the truck wearing a smile.
Life is good. Right?.
WRONG!!!!

I hooked this thing up, dropped the key for a radio check and just about jumped outta my skin.
I don't know for sure if I can even describe the noise!
It has a very loud growl, hum, low pitch squeal, and somewhat of a motorboat noise all at the same time.

Mic gain down doesn't change it. RF power down or up doesn't change it. Talkback off doesn't change it. Managed to get a radio check and the guy said. $@?/&&-'!....... what a noise.
So I took it back out. Put my spare 959 in and everything is fine with it.
That rules out everything in the truck.

Put this demon back on my bench and under a dummy load, I can't make it reproduce the noise no how!
I checked the mic ground. Even installed a cap in the mic plug just to be safe. Scratched my head for awhile and I just can't imagine what it would be. Turned everything down so PEP was all the way down to 10 watts and it still does it.
I'm pretty sure it's RF getting into the radio, but why does radio #2 work flawless on the same hook up??

If I'm way off track here with my suspicions, please feel free to voice your opinions. I am lost.

I added braided grounds, running a ext. speaker far from the radio, not over modulating. I wanna rule out feedback and I think I have.
Even on the bench, I can hold my RK56 right up to the speaker and key down to silence. But then again....dummy load.
Leads back to RF noise.
If anyone can help me solve this, I'll buy ya a beer! Or two! Or three! Lol
Whatever it takes cuz I'm about to get the hammer out!

Sorry for the long post and thanks for any possible help!
Joel
 
I did Robb. Actually I've tried 3 diff mics. The think that really has me stumped is the fact that my other radio ( which is set up identical) works just fine in the truck. Same antenna. Same coax. Same everything. I've been reading on Galaxy's site about resoldering a few caps lower to the board. Guess that will be my next attempt.
Is it possible that somehow it's injecting transmit RF from the antenna, back into the radio? SWR is 1.3 and swings back to 1.1 when I talk.
 
HMMM
1:3 swinging back to 1:1??
Was an o scope used to align the radio, sounds like it is swinging backwards, according to your meter, check the radio on the bench using avg setting of your watt meter, see if you have any forward output.

Also take a jumper, 6 foot or so and make an rf choke aka ugly choke , use this right after your radio IN THE TRUCK to see if you have cmc issues.

This RF choke is only for troubleshooting as it seems there are a few issues, the antenna system, and the radio.

Or just put the 959 that works in the truck, you did say they were both the same, and try the problem 959 on another vehicle to see if the same issues follow it.
 
wavrider said:
HMMM
1:3 swinging back to 1:1??
Was an o scope used to align the radio, sounds like it is swinging backwards, according to your meter, check the radio on the bench using avg setting of your watt meter, see if you have any forward output.

Also take a jumper, 6 foot or so and make an rf choke aka ugly choke , use this right after your radio IN THE TRUCK to see if you have cmc issues.

This RF choke is only for troubleshooting as it seems there are a few issues, the antenna system, and the radio.

Or just put the 959 that works in the truck, you did say they were both the same, and try the problem 959 on another vehicle to see if the same issues follow it.
Click to expand...
Thanks for posting Waverider.
An oscope was used to do the alignment. The radio has 30 watts of forward swing on average power setting.
I was always under the impression that a little reverse swing of SWR like that was normal.

Just to be sure on the "ugly choke"......
This issue is happening with the truck off, the ignition switch off, and the power wires connected directly to the battery. I did try grounding the radio chassis with braided straps. No difference.
Could you please tell me what "cmc issues" means?
Sorry if I seem ignorant but I'm pretty new to trying to diagnose radion troubles.

I think I may have failed to mention earlier that I don't experience this noise on SSB. Upper or lower.
It's only on AM
 
Last edited:
Robb....if that question is for me, the answer is... There's not.
Waverider suggested in a post above, that I try one for my problem.
I'm 100% certain it's in this radio. And not the truck
 

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