Another Galaxy Saturn thread. No V20 adjust. No front RF power knob adjust.

[vswr]

I know, I know. Not another galaxy thread. I did try asking through an old thread but got no response. Firstly to minimize redundant comments, I am a radio technician military trained. 22 years service. Lots of know how in repairs and restoring. All adjustments as per service manual done. Everything works with 1 exception. V20 no current adjustment. Transistor, diode, trim pot all disconnected and tested good. Reflowed all solder joints, no shorted caps. Swapped transistors left to right, still not adjustable. Transistors are not fake. I took them from a known good radio. Voltages are good. Bias resistors good.I just don't get it. Been struggling off and on with it between the shelf and bench, taking time outs, etc. I did not recap the radio. There are only 2 electrolytics in the finals area, and a bunch of disc caps. No short in them. There are 2 silver oxide caps to the right of V10. Both are not shorted. From the schematic, all associated parts involved with bias current test good. I just dont get it so Im appealing to you professionals to offer some insight into this problem.

 

[BayouRadioAmplifier]

First, I would put that shorting bar back in.
key radio up in LSB/USB mode, no audio into MIC,
and measure the voltage at either side of inductor
L50 to ground and adjust VR20 and it should go up to
.7 volts. it should be around .7 volts at L35 since
the bias works on that transistor when you adjust VR10.

and the bias adjustment usually works on fake transistors,
since they take an audio transistor and remark it as a 2SC1969 or
whatever.

 

[vswr]

Appreciate the come back. I will check on the .7 volts. Thats new info but the rest of what you said is appreciated but mentioned in my thread. Thanks.

 

[vswr]

First, I would put that shorting bar back in.
key radio up in LSB/USB mode, no audio into MIC,
and measure the voltage at either side of inductor
L50 to ground and adjust VR20 and it should go up to
.7 volts. it should be around .7 volts at L35 since
the bias works on that transistor when you adjust VR10.

and the bias adjustment usually works on fake transistors,
since they take an audio transistor and remark it as a 2SC1969 or
whatever.

Im yet to see a fake get any bias. I see them often enough. Never found one to be adjustable at all in either driver or final position.

 

[vswr]

Studying the scematic, and further testing shows that when powered down for the night, and then immediately setting everything up to adjust VR20 as per service manual, I do get my bias capabilities back as long as I dont reinstall the mirror board. Once its back in, then I key up, I get only 4 watts USB full whistle. AM I can get 10 watts. Pull mirtor board and retest, VR20 is again dead. This tells me current is getting there. I suspect a couple of disc caps and maybe R271 and L50 but L50 is just a solid 28 gage wire wrapped around a ferite bead. No doubt its all packed in pretty tight. I will do more testing on those voltages then unsolder the base and collector and inject a signal to see if it stays strong or drops out. I hate Galaxy Cbs. No wonder ebay is full of them.

 

[nomadradio]

Got in the habit of just changing R271, the 1 ohm quarter Watt with the ferrite bead slid over one lead. When a final fails, it will frequently pop this resistor. The new final now has no base-bias current.

Following the voltage into and out of R271 should show that nominal 2/3 of a Volt all the way to the base lead of TR55, or whatever the 'second' final is called.

73

 

[vswr]

Thats on the menu. Another weird thing that I found was a jumper very close to the finals that has a rubber insulator over it. Not heat shrink. Its a jumper that measures 25 ohms? ?? Should be a short! Anyhow? Other than that final issue, the rf power knob does nothing I tested it all the way from where it connects to the AM trim pot all the way to where it comnects to the VR803. This radio went through a real CB dummy that twisted and turned everything that could be turned. Its crazy.

Got in the habit of just changing R271, the 1 ohm quarter Watt with the ferrite bead slid over one lead. When a final fails, it will frequently pop this resistor. The new final now has no base-bias current.

Following the voltage into and out of R271 should show that nominal 2/3 of a Volt all the way to the base lead of TR55, or whatever the 'second' final is called.

73

 

[vswr]

UPDATE: R271 good, L50 good, R270 good, VR20 good, there is only 2 disc caps. C209 and c208. Coupling and a decoupling. If they come out to be good that its got to be a final that is an original and meter tests good that could be somehow fooling a meter test. Or the diode. We'll see.

 

[vswr]

Im yet to see a fake get any bias. I see them often enough. Never found one to be adjustable at all in either driver or final position.

.7 volts is good on both. R271 is good. injected 2k into the mic. Scoped it both transistors appear to be equal output on my scope but one has a slightly lower input to the base. I'll change the caps and retest it. If that doesnt fit the bill I have another good powered dx99v that I can strip the 2312s from and try again.

 

[brandon7861]

The transistors, aside from a pair of decoupling caps at their bases, are hardwired in parallel from an RF perspective. Checking each for an output doesn't really tell you much unless the other transistor is not there.

I have a hypothesis... Being the dual finals are hardwired in parallel, is it possible that you are mistaking the lack of current change on TP8 (which is for the driver, not the first final) with a change on TP7? Are you watching for current change on TP7 for both finals??? Both finals get their juice from TP7.

I only bring this up because I, someone only familiar with single-final radios, might mistake TP8 on the mirror board for TR56's supply not realizing the finals share the same jumper. I could see myself moving over a pot and out of habbit moving over to the other jumper too.

 

[vswr]

Yes. You are right. Both finals do meet up at the collector but are separate at the base by coupling caps. I could literally remove the collector and test each one that way. I've properly adjusted VR11 for 20 ma between tp 7 and 9. Ive adjusted vr10 for 50 ma. Very odd because the current creeps up to 50 ma then levels off. Moved over to adjust vr20 for my combined idle current of 100 ma. So making the mistake and thinking that vr11 driver bias us something I wouldnt do. I am after all a trained radio technician. My engineering skills are not half as good as a lot of members in this forum hence why Im asking. Its a very simple circuit but with all the magic that RF creates, it could be anything or any combination. Thanks for your response. I will lift the base and collector from each final one at a time and then make more tests. They are in a push pull config so very similar to how the 959 is laid out with only 1 final. I do have the mosfet conversion kit. If finding nothing but chinese crap continues, I will convert it.

 

[vswr]

Vr10 and 20 through tp 8 and 9. Sorry I forgot to expand on that

 

[brandon7861]

Moved over to adjust vr20 for my combined idle current of 100 ma.

Right, I was just making sure because...

I've properly adjusted VR11 for 20 ma between tp 7 and 9.

VR11 is for the driver TR44 and has nothing to do with TP7

So making the mistake and thinking that vr11 driver bias us something I wouldnt do.

VR11 is the driver bias and is checked via TP8.

I've properly adjusted VR11 for 20 ma between tp 7 and 9.

TP7 is the jumper that feeds BOTH finals TR43 and TR56. VR10 and VR20 are adjusted while measuring current between TP7 and TP9 for both final adjustments. After that, the current meter is moved to TP8 and VR11 driver is adjusted. My concern was not that you confused VR11 for a final bias, my concern was that you may have been using TP8 when turning VR20 when you should have been watching TP7 still.

Vr10 and 20 through tp 8 and 9. Sorry I forgot to expand on that

Thats my point right there....... TP8 is for VR11 driver bias, not VR10 and VR20 final bias

They are in a push pull config

They are not in push-pull, they are in parallel.

 

[vswr]

Right, I was just making sure because...

VR11 is for the driver TR44 and has nothing to do with TP7

VR11 is the driver bias and is checked via TP8.

TP7 is the jumper that feeds BOTH finals TR43 and TR56. VR10 and VR20 are adjusted while measuring current between TP7 and TP9 for both final adjustments. After that, the current meter is moved to TP8 and VR11 driver is adjusted. My concern was not that you confused VR11 for a final bias, my concern was that you may have been using TP8 when turning VR20 when you should have been watching TP7 still.

Thats my point right there....... TP8 is for VR11 driver bias, not VR10 and VR20 final bias

They are not in push-pull, they are in parallel.

You must be missing something. Im not a beginner in electronics.

 

[vswr]

Thanks to those who offered new information. Thanks to those who thought they were helping but turned it into an english exam. With all the fakes out there, I have decided to go the mosfet route and bec done with it. The mosfets are now installed and the radio is booming. Transistors have found their home in the trash. All is good, I'm no longer following this thread. Problem solved.