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

Wed, 18 Jun 2003 08:37:32 +0700

Thanks for the help so far.
Several mentioned the need to key the rig. Not the problem - I have
three TS940's here at the moment one of which is my own which I've had
for nearly 10 years, also a 930, so I'm quite familiar with it's tuner
operation. Problem is when pressing AT.T the sub display does NOT change
to ready, hence pressing the PTT has no effect since the tuner is, well,
not ready. The line that goes to AT.B on connector 1 pin 2, ATS, seems
to be the problem. Pulling this connector and putting a momentary short
on it cause the ready to appear and the tuner works fine when the rig is
keyed. Seem the line from Digital A isn't doing it's stuff and looks
very low when compared to a good one. This seems to make the fault
understandable when you see it is driving a dual 555 timer that needs
>1/3 of Vdd change to trigger. The fault also clears if swapping the
digital A board. Seems like the port expander IC6 is the problem. Just
an 8255, Z80 series port expander, I just didn't relish having to pull a
40 pin chip. Thing is the chip does work. I can see the trigger pulse
when the front panel AT.T switch is pressed it's just that the levels
are wrong, the logic high is going only to about 2.5 volts.

73
Martin, HS0ZED G4UQF

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Martin Sole
Sent: 17 June 2003 14:07
To: [email protected]
Subject: [Kenwood] Another TS940 problem. Auto ATU this time.

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

- - -

Your moderator for this list is:
Larry Wilson KE1HZ [email protected]

_______________________________________________
Kenwood mailing list
[email protected] http://mailman.qth.net/mailman/listinfo/kenwood