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Galaxy Saturn low transmit

Hawkeye351

Sr. Member
Jun 27, 2021
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747
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Got another Galaxy Saturn on the desk today. Someone stamped the sale date on the inside heat shield. Sell date was July of 1996.

Issue:
Low transmit power.

Evaluation:
Tested finals, driver, pre-driver, af regulator, Passthrough regulator, solder joints. All check out good, except for the last coil past the final which had come loose from the board. Resoldered and still same low output.

Checked each stage with my oscope.
Mixer shows good signal on output.
Pre-driver shows good signal.
Driver shows good signal.
Each final shows good signal.
Each stage shows amplification from the previous stage. Collector voltages are correct, base Ma is correct. Just low output.

Story is, a local just purchased it out of storage from a couple years, hooked it up and talked on it about a month or so until the power slowly dropped to 7w swing max in any mode.

After thinking it over, I thought about the output caps. I yanked both and tested each.

The 560pf tests as 325pf and not stable, changes each time I check it.

The 820pf tests as 796pf and is stable, doesn't change each time I check it.

Guess the 560pf shot it's wad....
 

Had some family issues come up. Getting started again later. Sorry for holding you guys up on the outcome of a few radios.
 
Got this one back going.

The 1 ohm resistors (with the beads on one lead) at the first final bias VR and at the second final bias VR was shot. Replaced both.

Both final bias VR adjustments were way out of tolerance. One showed around 28 ohms, the other showed around 34 ohms. Out of circuit of course. Replaced both.

Driver was good, both finals were leaning toward the minimum side on HFe. Replaced both finals.

Last coil in the output stage was loose from the board. Resoldered.

560pf 300v mica cap was way below it's tolerance. Was showing around 320pf.

A disc cap near the second final bias resistor (1 ohm) was leaned over and the leads were laying across a jumper. Straightened up all the parts in that area.

Output now:
AM - carrier - 1w up to 10w.
AM swing - 45w max PEP, 34w peak, 22w average.

SSB - 45w (gonna cut this back to around 35w)

VCO set according to service manual.

Buffers maxed out according to service manual.

Pll oscillators dead on the money.

Carrier oscillators dead on the money.

Transmit frequency dead on the money.

Power supply voltage set to 14.20v.

Finals, driver, Passthrough run very cool to barely Luke warm.

Now just gotta finish it up.
 

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