[Kenwood] 850 transmit audio garbled

[Joe Martinez]

My 850 has an odd problem, not addressed by the ALC repairs listed online. DC-DC board, DC-DC caps, and AIP board have been replaced (AIP fixed receive). Finals and drivers ohm out okay. 74LS145 (RF and Filter boards) check good. Receive is good. All symptoms seem interrelated.
 
Symptom 1: Transmit audio sounds garbled, like RF on the signal, due to DC ripple.
 
Symtom2: Monitoring the input and output of the DC-DC board I see a full wave ripple develop at key down on the output of the DC-DC board. Starts clean during receive, ripple starts at approximately the same time that garbled audio begins. So the scope sees ripple and a SPIKE! Goes away by disconnecting CN2 from the RF board. 
 
Symptom 3: My scope shows a large SPIKE.  
 
Power off/on,  CW or TUNE, transmit any band into a 50 ohm dummy load, at key down the outboard SWR/PWR meter rises and holds steady for approx 10 seconds then begins a slow oscillation, 50-40-50-40 watts, with approximately a three second cycle. Power output makes no difference on the three second oscillation cycle. I remove CN2, the final drive cable, from the RF board and everything on the input and output of the DC-DC board stabilizes. I also tried two different power supplies, just in case. 
 
Once the oscillation has started I can key down again and the oscillation starts immediately. I must turn power off/on before I get a ten second time of clean DC line at transmit. Then symptoms start again. Also output wattage/power seems lower direct into a 50 ohm load. Okay when run through a tuner into a dummy load. No change to the problem direct or through a tuner.
 
To RECAP: I checked the 14v input to the DC-DC board and when the garbled audio/ripple/oscillation begins and at the power oscillation (40w) low my scope shows a large SPIKE on the input and output of the DC-DC board. DC_DC board has a full wave ripple at this time. It sounds like all are related to a heavy load during key down.
 
Thank you in advance for any assistance.
 
Joe, NJ6OE at sbcglobal.net