Huge carrier on Galaxy 98 in SSB

[nbsr]

I got a Galaxy 98V in and I smelled the burnt from when the guy’s car door opened. I didn’t hook it up and just opened it. The amp exploded 4 out of 8 mosfets Not wanting to even dick around with those boards, where the transistor controlling the fan ops blows and couldn’t care less about an amp on “the bottom” setup, I moved on. Disconnecting the amp there was a 0.5 dead key swinging 52 on a LM 700. So I decided to make it into a 99V?. Fast forward into not doing a proper alignment, there was a carrier on USB and LSB. VR17 had no effect.

So I started from the start:
Removed the diode/resistor for power adjustment and went to original.

Mic gain down

Aligned LSB to specs

Aligned USB to specs

AM way out of spec. up tp 18 Mhz.

Checked the 10.695

I apologize to Sir Mr. Lou Franklin, I never did make that crystal checker that you told me to do. Humble apology .

Replaced the crystal, realigned USB, LSB, AM.

Adj driver and finals to 100ma and 3.8v

2.5 dead key swinging 52 on AM,

30 watt dead key on SSB swing dick on SSB.

VR 17 no effect.

R 276 still in place, so the limiter is still there?

Further digging, Q39 was removed (what a turd).

Replaced the 945

AM 2.5 swinging 10

SSB 30 watt carrier.

What did I overlook?

 

[sp5it]

Parasitic oscillation.

 

[nomadradio]

This is when having an inline frequency counter on your dummy load pays for itself. If the frequency of your sideband carrier matches the channel selected, that's one cause to pursue.


BUT if the counter shows a frequency not controlled by the channel selector, this is a very different problem with a very different cause. And this is what I think you'll see if you put a counter on this radio's antenna output.

Finding out which of those two ways to look further is where I would start.

After tightening the circuit-board mounting screws on the radio's PC board.

73

 

[nbsr]

Thanks Nomad, my oversight for not including it.

USB 26.96504
LSB 26.96505
AM 26.96506

Should I look at IC6 or Q46?

 

[nomadradio]

IC6 is the balanced modulator, the source of the sideband transmit signal, and it's supposed to cancel out the carrier in sideband. VR6 is the carrier-balance trimpot. If someone was randomly twisting adjustments looking for another quarter of a Watt it may be wockerjawed. IC6 is one of those "never goes bad" parts. Nothing is fail proof, but that chip has an almost-perfect service record.

If it had a lot of carrier on one sideband, but not the other I might suspect the sideband filter FL3. When FL3 fails only one sideband tends to lose carrier suppression. The balanced modulator chip cancels out most of the carrier, but the crystal filter finishes the job.

But only when it's working. Can't remember seeing one that forgot to reject a carrier for both sidebands. Ever.

73

 

[nbsr]

I have Franklin's service manual from the 90s. The voltages don't match to what is published for IC6. Would that have changed over the years? I'm enjoying the experience but wondering if I lost a logical approach.
Mike how do I go about finding/fixing your suggestion? Honestly, I wouldn't know where to start.
BTW, thanks for everyone's insight, I truly appreciate it.
Mark

 

[nomadradio]

Leads me to wonder if the 9-Volt regulator Q37 has run away, feeding too much voltage to that circuit? The center leg of Q37 should not have more than about 9.5 Volts DC on it.

Grasping at straws, could the trimpot VR6, the carrier balance be damaged?

73

 

[nbsr]

Old habit, I always check the regulator, 13.8, 8.6, 12.4. I'll pull VR6 and check it today. Thanks

 

[nbsr]

VR 6 is 9K and operational out of the board but has no effect in adjusting carrier suppression. Attached are voltages of IC 6 and Q34.

IC 6
AM U L
6.38 6.05 6.09
8.26 8.28 8.3
3.15 3.08 3.1
0.097 0.95 0.96
8.19 8.2 8.22
1.49 1.56 1.56
0.1 2.95 2.95

Q34 C114
AM SSB
0.09 0.9
0.1 3.0
6.0 0.09