Kenwood TS-9000 Low output on SSB

[mschmitz57]

I picked-up a used TR-9000 that has a problem with SSB transmit.
It transmits briefly on SSB for a second or two, then drops to zero output. Then If I switch the mode switch back to FM momentarily then back to SSB I can briefly transmit again. My friend can hear me normally but the output dies out. Both USB and LSB behave in the same way.
This radio works fine on FM. I adjusted the VR's for 11 Watts Hi, 1.25 Watts Low.
SSB receive is fine also. I tried fiddling with the SSB mic gain but no help.

Any ideas?
Mark

[mschmitz57]

Here's a little more detail. When I got the radio the low power setting output was around 1/4 watt and high power was set to around 14 W.
I adjusted both of these back to factory spec of 1W and 11W using the internal pots.

Inside of radio is in very nice condition with no visible damage or repairs.
I can briefly drive the SSB output up to full power by whistling into the mic (dummy load) but it dies back to zero in about 2-3 seconds.
Voice modulation sounds fine to my buddy for the 2-3 seconds while the RF output lasts. Output dies gradually, not abruptly.
The only way to reproduce this is by switching to FM mode momentarily, then back to SSB. It almost seems like the swr protection is kicking in.

Again, the FM mode works fine. SSB receive also fine. CW transmits a full power carrier when depressing the mic key.
This radio had 3 small wires dangling for a missing tone box that were hanging out of it that were soldered to the rear of the tone
jack inside the rig. I removed these.

All front panel controls work normally.
I went through and reseated all the wiring harness connector and checked for loose components.

Clearly this seems like somthing specific to SSB voice modulation not getting through to the PA.
I tried freezing areas of the internals with no results.

Thanks,
Mark

[5B4AJB]

try replacing the P.A. sounds like it's been cooked'

hmm - F.M. is OK? did you do try a reset?

[mschmitz57]

No, the PA is fine.
Like I said, radio puts out full power (11 watts) on FM and CW.
My guess is somthing exclusive to SSB circuitry (perhaps the mixer or SSB filter?).

[redwa8rli]

No, the PA is fine.
Like I said, radio puts out full power (11 watts) on FM and CW.
My guess is somthing exclusive to SSB circuitry (perhaps the mixer or SSB filter?).

Mark... w/ the limited info thus far, I would check the SSB filter crystal for possibly being cracked/shattered, loose connection in holder and / or bad/leaky padder capacitor.

[KM3F]

On the internet, download the user manuel with the drawings and trace how the SSB circuit is switched in and what componants are in that ckt line.
It could be as simple as a resistor that has gone up in value from heating.
If all the other modes work at full output with no slump in power, the SSB chain has a fault.
Basicly, audio is fed to a balanced modulator ckt.
The balanced modulator has a local oscillator signal injected into a balanced bridge type circuit.
As audio changes the balance, the ckt outputs 2 side bands.
These side bands are applied to a crystal filter that only passes one side band depending on which one you selected from the front panel and passed on the remaining side band to the final power amplifier circuit.
Look in these parts of the circuit for some issue.
FM does not use the SSB ckt so has no issue.
Just for info: The radio does not have AM but "if it did" it's possible the AM may/might also have an issue since it would use the SSB balanced modulator in an "unbalanced" condition to obtain an AM carrier, that is a common way to get AM in many radios..
Good luck.