[Kenwood] Another TS940 problem. Auto ATU this time.

[Martin Sole]

Hi,

Well I got this particularly abused TS940 all fixed and it's been
sitting on the shack floor for a month or two waiting for the owner to
come calling. He finally did and I showed him how his radio was now
working great. Right up until I tried the auto ATU. Selecting Auto/Thru
sets everything up right, the relay closes etc. Pushing AT.T does
nothing. Looking at where this comes from, the dreaded digital A board,
I see it outputs from 1 bit of a port expander. Pin 20 of IC6. With this
line disconnected from the auto ATU board I see only 2.5 volts on it,
not the 4.8 I see on another one, also see about 24K between pin 20 and
19, a good one shows infinite.

Does it seem likely that the port expander has died? I can still see the
trigger pulse on the line and was wondering if I could arrange some sort
of extra pull up to force this line high so that the pulse would
properly trigger the following monostable.

Any ideas?

73
Martin, HS0ZED G4UQF