959 has low modulation

[wavrider]

http://www.w8ji.com/common_mode_current.htm

common mode current good read

 

[wavrider]

take the dummy load to the truck, disconnect antenna connect dummy load see if the noise happens again, if it does not happen then antenna system or coax

 

[loosecannon]

so you have a dual final 959?

did you buy it like this off of ebay or did you do the mod yourself.
959's do not come from the factory with dual finals.

it sounds like the problem you are having is that the radio works on a dummy load, but not on the antenna right?

do you have a low pass filter?
if so, put it in line between the radio and the antenna and see if this changes the performance any.
please post back the results of this test.

my guess is that you have done some mods to the output section of the radio that have caused a high harmonic content.

your dummy load wont react to this, but an antenna will.

fundamental signal is 27mhz. 2nd harmonic is 54mhz. your antenna is tuned for 27mhz.
too much signal at 54 mhz will reflect right back into the radio, which could have caused the feedback you experienced.

so, please list any and all mods done to the TX of this radio if you don't mind, and we will start there.
LC

 

[Jdb0367]

I don't know if I'm on to something here finally.
Checking voltages on the TX Mixer (IC9), I found a couple voltages that seem to be off.
Heres what are called for, and what is measured:
Pin. Measured.
1 - 0.00TX. 0.00
2 - 8.23TX. 7.67
3 - 8.23TX. 7.67
4 - 0.00TX. 0.00
5 - 8.23TX. 7.68
6 - 0.00TX. 0.00
7 - 3.14TX. 3.46
8 - 2.70TX. 3.51
9 - 0.00. 0.00
10 - 0.87TX. 4.6mv
11 - 1.56TX. 4.6mv
12 - 0.87TX. 4.6mv
13 - 1.56TX. 5.1mv
14 - 0.00. 0.00

Should I be concerned with pins 10,11,12 and 13?
Thanks fellas

 

[Jdb0367]

Loosecannon!!
Thank you for chiming in here. I do believe you are absolutely correct.
I did the dual final mod myself. Followed the procedure given by Rick Jackson.
Copied exactly per his instruction with the exception of the IRF520's.
I used 3 FQP13N10's instead.
Power Amp (Q54) was switched to a 2SB817
AM AF Amp (Q55) was switched to a 2SA1012

I do not have a low pass filter to try

 

[loosecannon]

glad to see you got the mod working. (well sort of LOL) it can be a bit of a pain in the butt to get it right.

can you link me to the procedure you used? i would like to see it.

do you have a frequency counter?
if so, can you check TP3 on AM channel 20 and tell me the frequency you measure there?

how much of the alignment were you able to do?

as for the TX mixer, pins 10 and 12 have to do with how broadbanded the chip's response is, and this gets modded sometimes when extra channels are added in an effort to keep the power output the same across the new freq. range.

we won't worry about the different readings there yet, because this reading may be caused by the weird readings on pins 11 and 13. Can you confirm that R261 (the resistor that connects to these two pins) is a 1K ohm resistor? (brown-black-red)

now, pins 11 and 13 are 1/2 of the mixer inputs. pins 7 and 8 feed the 10.695mhz signal in, and pins 11 and 13 feed the 35mhz VCO signal in. mix them together and you get a 27mhz output.

so right now, lets concentrate on that VCO input to the TX mixer, and i want to make sure that we are on the same page with the voltages you are measuring.
on pins 11 and 13, you should be reading about 1.56 volts DC. you are measuring about .005 volts DC on these pins, right?

check L43, the VCO input to the TX mixer. does it seem to peak, or does the output stay the same no matter where you turn it?

if it does peak, does it seem to peak with the ferrite slug sitting perfectly flush with the top of the can?

lastly, did you change L35 to a 4 turn coil when you did the dual final mod?
it is a 7 turn coil in stock form. if you didn't you will need to remove three turns from it, scrape the enamel off the new end, and cut off the excess. dont do it yet though, lets get your radio working first.

lets also make sure that L31, L30, L29, and L28 have not been messed with, spread, compressed or otherwise.

i know i gave you a lot to get to, and am asking for a lot of information, but we need to get certain things out of the way before we can really start troubleshooting.
LC

 

[Jdb0367]

glad to see you got the mod working. (well sort of LOL) it can be a bit of a pain in the butt to get it right.

can you link me to the procedure you used? i would like to see it.

do you have a frequency counter?
if so, can you check TP3 on AM channel 20 and tell me the frequency you measure there?

how much of the alignment were you able to do?

as for the TX mixer, pins 10 and 12 have to do with how broadbanded the chip's response is, and this gets modded sometimes when extra channels are added in an effort to keep the power output the same across the new freq. range.

we won't worry about the different readings there yet, because this reading may be caused by the weird readings on pins 11 and 13. Can you confirm that R261 (the resistor that connects to these two pins) is a 1K ohm resistor? (brown-black-red)

now, pins 11 and 13 are 1/2 of the mixer inputs. pins 7 and 8 feed the 10.695mhz signal in, and pins 11 and 13 feed the 35mhz VCO signal in. mix them together and you get a 27mhz output.

so right now, lets concentrate on that VCO input to the TX mixer, and i want to make sure that we are on the same page with the voltages you are measuring.
on pins 11 and 13, you should be reading about 1.56 volts DC. you are measuring about .005 volts DC on these pins, right?

check L43, the VCO input to the TX mixer. does it seem to peak, or does the output stay the same no matter where you turn it?

if it does peak, does it seem to peak with the ferrite slug sitting perfectly flush with the top of the can?

lastly, did you change L35 to a 4 turn coil when you did the dual final mod?
it is a 7 turn coil in stock form. if you didn't you will need to remove three turns from it, scrape the enamel off the new end, and cut off the excess. dont do it yet though, lets get your radio working first.

lets also make sure that L31, L30, L29, and L28 have not been messed with, spread, compressed or otherwise.

i know i gave you a lot to get to, and am asking for a lot of information, but we need to get certain things out of the way before we can really start troubleshooting.
LC

Here's the link to the mod written by Rick.
I'll let you look it over while I'm soaking in your response.

http://www.cbtricks.com/miscellaneous/fet_papers/mosfet_conv/graphics/6900xxx_ssb_mosfet.pdf

I do have a frequency counter. I don't have a spectrum analyzer but I do have a scope, AF and RF sig generators and some good voltmeters.
Thanks for sticking with me here Loosecannon!
Hopefully we can fix this.

 

[Jdb0367]

Ok.....here is the info you asked me for..

With mirror board still in, AM chan 20, freq. cntr on TP3
16.50985 with mic gain off
16.586 and drifting with mic gain full open, no mod.

L43 peaks just fine and @ peak, the slug appears to be roughly 50% down the can.

I did change L35 to a 4 turn coil

L31 looks factory
L30 has be spread a bit ( not by me)
L29&28 look like they may have bit touched but not bad. (Again...not by me)

I am reading DC Volts on the mixer pins and the voltages I posted are what was read.

I will post my findings on R261 shortly

As for the alignment..... I thought I got thru it all really well.
They radio responded nice and everything on my scope and wattmeter looked good.
I'm by no means an expert on radios but I did buy this thing used and it didn't perform well at all.
It still doesn't perform well. Lol
But I am making progress with your help.
Thank you much so far

 

[Jdb0367]

Yes it is Brown, Black, Red on R261
1K ohm resistor

 

[Jdb0367]

Just double checked voltages at the mixer pins and pin 11 is 4.6mV and pin 13 is 5.1mV

 

[loosecannon]

ok, i just read back through the thread, as i don't want us to be chasing our tails.

first thing i noticed was that the radio does not do this on SSB.
that is a clue!

second thing i noticed was that you have another 959 that also has this same dual final mod done to it, but is a china built radio, and this radio works just fine in your car on AM and SSB.
please correct me if i am wrong on any of that.

next thing is that the dual final mod you used is for the ranger 6900 series boards, and you have the 696xxZ series board. they are very similar, but im not sure they are exactly identical. it does appear that the mod worked for you, but i am curious to know if you had to change anything in the instructions to make it work.

Wavrider had a really good suggestion that i somehow missed.
he asked you to take your dummy load out to the vehicle, take the antenna off the mount, and connect your dummy load in place of the antenna.
then try the radio and see if it does the squeal thing using the dummy load as your mobile antenna.

if your antenna doesn't have a convenient SO-239 connector on it, you can cut the end off of a piece of coax, put some lugs on the center conductor and shield. (those leads should only be about three inches long or so)
now you can connect that coax to your antenna mount instead of the antenna, and connect the other end of the coax to your dummy load.
let us know what happens.


that being said, i do think you have a problem inside your radio, and right now im thinking that it has to do with poor soldering somewhere on the board. (factory soldering, not necessarily yours)
I have already repaired two of these vietnam 959's and both problems were due to poor soldering.
get out the magnifying glass and spend some time going over the board. especially the pll and vco sections, along with the TX strip.
if you see anything funky, don't just re-heat the connection; flow some fresh solder in it.


you should be able to get a VCO reading at TP3 without transmitting, and that's the reading im interested in at the moment.
HOWEVER!
you really helped things along when you posted what the freq counter was doing during TX!

first, another question of course.
is the clarifier unlocked?

next, i want to make sure that when you are peaking out the TX adjustments, that you are using a modulated tone and not tuning for max deadkey.
re-assure me on that one.

make sure Q39 (amc) is in place and doesnt have a leg clipped. you will have to look closely for that one.

to give you something to mess with till i get back to this thread tomorrow, go through the VCO alignment section on cbtricks, and make sure you have peaked L15 as per the instructions.

now set the radio for channel 20, AM mode, receive mode, clarifier centered at 12 o'clock.
connect freq counter to TP3, and adjust L20 for 16.5100 mhz.

remove the mirror board, and key the radio. the freq counter reading should not move.
it should still read 16.5100mhz.
if the clarifier is not unlocked, and the freq counter does shift to a different freq, but stays steady at the new freq. then adjust VR7 in TX mode for 16.5100mhz.

if the clarifier is unlocked and the frequency changes when you key the mic, or if it jumps around when you key the mic (it seems like it does) then this is a real problem.

bad soldering could cause this easily.

it seems to me right now that your PLL will lock, because otherwise you wouldnt have any transmit, but the VCO frequency isnt staying steady at TP3 for some reason.

if you look at the schematic, and find TP3, you can see that it branches off in two directions, one goes to the receiver mixer, and the other goes to the transmit mixer.

if your freq reading in receive is solid and correct, then that branch is ok.
follow that branch to the TX mixer and check the soldering of that path.

sorry if it seems like we aren't getting anywhere, but this is a wacky problem, and its tough to troubleshoot this type of thing without being there.
more tomorrow after i see the results of your testing along with your answers to my questions.

no hammers!!!!
LC

 

[Jdb0367]

LC,
The hammer is looking like a good option at this point!! Lol

Last post for me tonight also....

You are correct on me having two 959's
They both have the same dual mosfet mod done in the exact same way. I did them both myself.
I did not have to change anything in Ricks instructions to make the mod work in either radio.

The Vietnam version ( with the really shitty soldering ) is in my vehicle now and it works fine.
P.S.
I spent hours on that radio with a magnifying glass! Isn't that some quality craftsmanship???

Now back to the problem at hand. ( China 959 )

The clarifier is not unlocked in this radio.

I am using a 1 KHz tone to make my TX adjustments.

Q39 is there and not clipped. ( I installed a new one just because)

I've double and triple checked the VCO alignment and it's spot on.

I will do the other recommendations tomorrow. Well I guess at this point, it's more like later today....... Yawn

I wanna run this VCO pin voltage by you before I go.
TP3, R259 and R261 are showing the 5mV that are at pins 11 and 13 on the VCO.

I've traced that circuit back to Q18 and Q19 to find voltage.

Legs S on Q18 and 19 show 1.9 V
C56 and C57 are fed that same 1.9 V but only have the 5mV coming out of them.
This is the same low voltage that goes thru JP204 and to TP3, R259 and R261.

Is the low pin voltage at the mixer causing my issue?
Or am I delirious from lack of sleep?

Anyways....... I will do your other recommendations after work today, and report back.

Thank you so much everyone
I really do appreciate the help that's been givin so far.

 

[Robb]

One thing about peaking TX coils that really doesn't seem to get much exposure is that they can be over-peaked. As long as one sees the watts going up and up on the watt meter, one might assume that all of those watts are all clean watts. Not so. There are a couple of ways to determine this situation.

First is to hook up an o-scope on your sensing line to the watt meter to see if the waveform is remaining faithful to the same audio signal being put through the mic - ie - the sine wave stays true - no negative peak clipping. You will see this change when you go over the limit and over-peak the last couple of coils as the signal will get distorted.

Another way is not anywhere near as accurate, but it should be used as a final test. That would be to have another radio hear the output signal of the radio under test. Not an audio sample from the audio circuit either, as it is not the same, but an independent radio that is receiving the signal as transmitted. Little tricky to do this; there are a few small issues one has to overcome to make this happen. Another thing is that it is not anywhere near as reliable as the first method. In conjunction with; but not without the first method concurrently; never trusting method two on its own, as the ear is too easily fooled.

I have had to take this approach on Galaxy radios in particular. Too easy to over peak. Goes to prove once again that tuning a radio shouldn't be passed off as a simple operation that anyone can do with merely a watt meter and saying 'auuuudio; auuudio' into the mic to achieve a proper tune, and that there is no problem or mistakes made by this method. Nothing could be farther from the truth.

Not implying or saying that you are doing this, just thought it would be best to keep the tuning method pristine when working on the Galaxy in particular, and any radio in general . . .

 

[loosecannon]

JDB, it was this statement of yours that prompted me to ask you about the VCO alignment:

"With mirror board still in, AM chan 20, freq. cntr on TP3
16.50985 with mic gain off
16.586 and drifting with mic gain full open, no mod."

your VCO alignment cannot be "spot on" if this is the case. if your freq counter starts bouncing around, or doing anything but sitting there solidly displaying 16.5100 mhz then you have a problem with the VCO.

from that statement, it would seem that you were testing it in TX mode, which is where you are having a problem.
the chances of those two things not being related is low.

so if you tell me that the VCO alignment has been checked and re-checked, and you are considering it to be good; then somehow the situation you were having before that i quoted above is now not happening?
please give me some details on that so we will be on the same page.

lets try something else real quick. first set the radio up like this: ch. 20, AM mode, clarifier centered, mic gain all the way down.

now remove the mirror board in the back, and connect your freq counter probe to the center pin of the antenna jack, negative lead to radio chassis. (freq, is AC so it doesnt matter if its PC board ground or chassis ground)

now key the mic and read your actual transmit freq.
it should be 27.2050 mhz, and should not vary at all.

let me know what you find there.


as for the voltage measurements, remember that a capacitor will not pass DC voltage, only AC voltage.
if you see a series capacitor in a path you are following, you can be sure that it is a signal path, and not a DC voltage path.

Q18 and Q19 are part of the receive mixer section and do not provide any DC voltage to this section. you can leave them be.

if you look at the schematic, you can see that pins 11 and 13 are connected together through the secondary of L43, and there is no DC connection for them to be pulling any DC current from.
the DC voltage you measure at the pins is generated internally.

you actually have the greatest source of answers sitting right in front of you!

you have a working DX959 that you can sit right next to the suspect one, and compare voltage readings.
if i were you, this is what i would be doing.

you can also swap parts that you are unsure of as a way to find your culprit(s).

i dont want to go much further until i get more answers from you on the VCO thing, and the other tests.

good luck, i'll be checking back over the next couple of days.
LC

 

[Jdb0367]

LC
Frequency counter on TP3, channel 20 AM, mirror board in, freq. reads 16.5100
Mirror board removed and mic keyed, freq. reads 16.5100 and holds solid

Freq counter on center pin at anten connector, mirror board removed. Counter reads 27.205 and holds steady.

When I said it was drifting last night, it's because I was keying the mic with the mirror board in place and turning the mic gain.
I just tested everything tonight as you stated and it does in fact hold steady.

Please excuse my ignorance but why if I key the mice with the feq counter in antenna center pin, and speak, the counter goes from 27.205 to 23.XXX and 28.XXX and anywhere it feels like going. Is it just because of my voice?

Everything with the VCO seems to check out at this point.
Noise is still there when I take it to the vehicle.

I didn't make an adapter for the dummy load at the antenna.
I just don't feel the need.

I put my Cobra 29 in tonight and made a contact 12 miles out while my antenna was about 2 inches from touching my carport ceiling.

I'm convinced it's in this radio