Galaxy Dx-959 No Am Modulation/power/transmit

[Ranch55]

Split the baby and set them both to 3.75v; should be OK.

My current problem is that after replacing both Mosfets, and setting the driver at 3.7v and the final at 3.5v, all else seemed to align just fine.
All seems good, until I key the radio on SSB, no modulation, and the radio keys up with full carrier, on SSB....... what the heck ?????

 

[Robb]

AM regulator; that is what this thread is all about.
Start reading it from the beginning.

 

[Ranch55]

AM regulator; that is what this thread is all about.
Start reading it from the beginning.

I have read this complete thread. I am not sure how it may address my problem, or I'm not understanding all I have read.
My radio has AM modulation and carrier. It will dead key 4.5 watts and swing up to about 17 watts.
On SSB mode, when I key the radio, it has a carrier with no modulation present. When I do modulate, it has a swing up to about 18 watts or so, as one would expect. Stop modulating and it will decrease back down to what appears to be a carrier.

 

[Robb]

Improperly adjusted VR6; or VR6 isn't working. Other than that, it could be something in that circuit.

http://www.cbtricks.com/radios/galaxy/dx959/dx959_adj.htm

 

[Ranch55]

Improperly adjusted VR6; or VR6 isn't working. Other than that, it could be something in that circuit.

http://www.cbtricks.com/radios/galaxy/dx959/dx959_adj.htm

Okay, thank you. I will check on that. I appreciate your input.

 

[357]

Q34 could be dead or D57

 

[Robb]

Also check Q55 . . .

 

[Ranch55]

Improperly adjusted VR6; or VR6 isn't working. Other than that, it could be something in that circuit.

http://www.cbtricks.com/radios/galaxy/dx959/dx959_adj.htm

VR6 is working. I can see adjustments made on watt meter and on the oscilloscope.

 

[Ranch55]

Q34 could be dead or D57

will check that next , and Q55 as Robb suggests.

 

[Ranch55]

Okay, this is what I did find.
I contacted Galaxy Radios technical via email. Technical called me about an hour later on the telephone.
They said they had seen this issue several times in this radio and in their 10 meter radios. (SSB carrier when keyed without any modulation)
They recommended turning the Mosfets bias voltage down from the 3.7v~3.9v range, and start at 3.2v bias. Go up from there .1v at a time until the the SSB carrier appears and then back down .1v .......
It worked great. The SSB carrier is now gone with bias voltage on driver and final set at 3.5v ..... If I go to 3.6v, the SSB carrier appears again. So, 3.5v it will be.
Voltages at Q54 and Q55 check out as per specs, as well as Q56 and Q34.
VR6 now balances out very well also on the oscilloscope.
Thanks to all on this forum.

 

[Robb]

Congrats . . . but . . .
NEVER heard of such a thing . . .

The only possible answer that I can see is that there must be some internal feedback happening somewhere.

You did turn down the mic gain on the radio to zero before you tested - right?

 

[kaos513]

I took my time and testeed all diodes i found my issue it was d4 was blown out .

 

[Ranch55]

Congrats . . . but . . .
NEVER heard of such a thing . . .

The only possible answer that I can see is that there must be some internal feedback happening somewhere.

You did turn down the mic gain on the radio to zero before you tested - right?

Yes, mic gain turned down to zero on all adjustments, except when required for a 1kHz signal.
As far as some feedback causing it, maybe so, but I do not know where to look for it.
If I turn the bias voltage up to 3.6v, the SSB carrier shows up. If 3.5v, it goes away.
Q54 has been replaced with a new B817, and Q55 has been replaced with a new NTE153 .......

 

[Ranch55]

I ended up by replacing Q49 and Q47 with FQP13N10 MOSFETS. I replaced Q55 with a NTE153, and Q54 with a new Palomar MAX MOD regulator. (Upgrade for the 827, 817 )
I set the bias voltage for Q49 and Q47 at 4.0 volts.
I balanced SSB with VR6 on a scope.
The SSB carrier that the radio had disappeared. Output power has increased slightly, about 6~8 watts PEP.
Scope shows clean modulation. I did not crank up the ALC to maximum. Only to get max output with clean modulation.
So far, it seems to be doing well. If any issues crop up, I'll update the forum.

 

[VB2021]

Problem found. Found another bad capacitor. Replaced and she is fully running again.

which cap did you find blown ??