[Hallicrafters] SR-400A VOX problems

[Don VE3HUR]

The VOX on my SR-400A clips off the first dit of a CW character. It's
not a sharp clipping but, rather, a slow dit/dah seems to fade in.

The sidetone sounds ok and there is 12V P-P at the junction of R143 and
R144 so I presume that the sidetone generator is ok.

As per the manual, I measured the resistances around V19 and V20 and all
were ok except for V19 pin 1 measuring 242K (should be 130K) and V20
pin 2 measuring 3.9M/10.1M (should be 3M/7M).

Voltage measurements on V20 were within tolerance. However, on V19 pin 1
was only 81 volts (should be 135). Pin 7 was -106 volts (should be -130)
but since that is to cut off V19A it should be ok. All voltages are for
CW operation. The +230V line is ok and the bias line is -135V.

I checked the resistors around V19 and V20 by measuring them in circuit
and they all measured within tolerance except for R159 which tested ok
when removed from the circuit.

For test purposes I've disconnected the anti-trip by disconnecting R157.

The two times I operated SSB I was told my audio was ok. I used an
old Turner desk microphone and didn't have gain problems.

Does anyone have any suggestions about why V19 pin 1's voltage and
resistance are so far off. Also - any suggestions about diagnosing the
VOX problem?

73, Don VE3HUR