SX9K uncontrolled receive volume

[Bobby]

I have a Synor X 9000,VHF, that has developed a problem with the receive audio. It is NOT DISTORTED, but it now runs very high (like a "10 " setting). When I toggle the volume down, it just about shuts completely off like on a "0" setting, with nothing in between the "10" and the "0"?????

I changed to another SX9K, and control head, individually, with the same cable, and they are OK. I then swapped control heads (a good control head from another radio) and it was still distorted on the problem radio. I then put a "good radio" on the control head of the bad radio, and audio still runs high.

So it is not the cable or control head, but the radio.

Any thoughts to a solution?

Bobby

[Mike B]

The volume control function is a clocked synchronous serial data stream from the radio drawer U500 pin 16 Preamp Data, U500 pin 14 Preamp Clock, U500 pin 25 Audio Mute and U504 pin 12 Preamp WE (write enable). These 4 digital control lines go to preamp chip U302. If its not an audio amplifier problem like out of control amplification gain, then its either the radio drawer microprocessor system or the preamp chip.

There is no analog volume control circuit inside the control head, the control head is all Systems 9000 digital data telling the radio drawer U500 microprocessor to change the volume setting.

The easy fix is just replacing the personality board (if you are comfortable doing this),
http://www.onfreq.com/syntorx/syntorx9k ... l#bot_view
http://www.onfreq.com/syntorx/syntorx9k ... l#x9kperbd
setting the jumpers:
http://www.onfreq.com/syntorx/syntorx9k ... l#x9kjuper
readjusting the R111 compensation (very important if you use DPL and critical for low band), then the R108 deviation, and usually not but sometimes the R213 squelch threshold.

You could also trouble shoot the existing audio amplifier, starting with the preamplifier. You could use your good radio as a reference for oscilloscope measurements of U302 pin 14 (the audio output). Using a service monitor to modulate a steady amplitude audio tone through the antenna input try changing the volume setting and seeing if the preamplifier output levels are predictable and reasonable. If the preamp doesn't work you have a preamp or digital control problem, and if the preamp works you have a downstream audio problem. You could also check U302 pin 15 the preamplifier audio input if U302 doesn't work.

There is a Rx routing troubleshooting flow chart in the Syntor X 9000 service manual. The compensation adjustment instructions are located there also.