Time for maintenance. The VOX is inop. 15 meters is inop. First thing is VOX mostly because it's AF and easy to reach. To help me work I made a schematic of just the T/R switching and VOX so I could understand what's going on. Using a second project 830 with an operating VOX but other issues as a test mule.
Click for the full size schematic. It's set to open in a new window or tab. The point of the schematic is to pull JUST the T/R switching and VOX off the convoluted Kenwood oem world map; so someone of my limited skill-set can more easily follow and try to understand.
Just sitting there in receive Relay-1 is not energized, Q17 of 'OFF', Q16 is 'OFF' and Q15 is 'ON' and Send Receive S17 is 'open'.
Relay-1 on the Audio AVR board is controled by Q17. Q17 is controled by either the Send/Rec switch S17 (or Mic PTT) (SS line) or by VOX action via Q16. During Receive with no VOX action (Q16 off) and S17 open (bias string R67 D13 R69 R74 float) Q17 base is held high to the emitter voltage and Q17 is off. If S17 base bias is grounded by S17 or Q16 is turned on then Q17 base is forward biased and Q17 is turned on energizeing RL1 to transmit.
VOX action is controled by microphone audio (VXI) via the Q9 Q10 Q11 amplifier or CW sidetone audio via D9 and anti-VOX via sampled speaker audio (SP) to Q5 Q6. Opening S14/VOX by rotating VOX Gain clockwise (CW) lifts Q16 base from ground so that Q16 is controled by Q15 which is controled by Q12. In receive with no VOX action Q12 is off allowing Q15 base to be forward biased by 9V via the VOX Delay VR5 (VXD) through R69. Q15 is normally 'ON' holding Q16 off and Q17 remains off. With VOX on S17 Send/Rec or PTT will still control Q17.
Either mic audio or CW sidetone forward bias Q12 grounding Q15 base turning Q15 off and Q16 on. Q17 base is forward biased by current throught R74 Q16 R73.
Anti-VOX from the audio amplifier is through Q5 Q6 to Q7. In this case if Q7 is turned on by speaker audio it acts to ground Q12 base holding Q12 off.
D11 Q13 C49 with VR5 and R69 form a timing circuit for adjustable VOX delay. In receive Q13 base and emitter are approximately equal voltage and Q13 is off. C49 is at the same voltage as Q13 emitter. VOX activation turns Q12 on bringing Q13 base low Q13 is on and C49 is discharged through Q13. When VOX releases Q12 turns off Q13 turns off and C49 is charged by the 9 volt supply through VR5 VOX delay and R69. Variable VR5 controls the time constant and VOX release delay.
All voltages measured with VOX Delay and VOX Gain 1/2 (12 o'clock) and a 1kHz 1.5mVrms into the Mic connection. With 1.5mVrms in the VOX Gain at 1/2 just triggered at the voltage shown on the schematic.
30mVp-p at connector 1-5, VXI, from IF board 9-1. This mic audio is taken from the IF board before Mic gain, which has no effect on VOX operation.
700mVp-p at Q12 base. There is also a DC level change from 0.0V to 0.18V
Click on image for full size. Only components part of the VOX are marked. This is an early board and includes C48 and Q14. Late boards have a jumper in place of C48. Component markings are still hard to find and read. I'll have to research for better.
Connector: 1-3 SSB white/red/orange, 1-5 VXI blue shielded white signal, 4-1 SS white/green, 4-2 VXS white/yellow, 4-3 VXD white/blue, 4-4 VXG white/red, 5-4 AV white/red, 5-5 SS gray.
Diodes D6 through D10 and D13 1S1555 to my untrained eye is a low leakage low C part. Probably garden variety 1N4148 would do. A good replacement looks to be Vishay BAV19.
Diode D11 1N60 germanium low forward voltage. 1N34, 1N270 or STMicro BAT43 (Schottky)
Q13 2SA1015(Y) PNP readliy available and inexpensive.
Q16 2SC945(Q)
Q17 2SA562(Y) PNP switching and gp. Readily available inexpensive.