[Kenwood] Amp Keying Relay on 940

[Gary McAdams]

Fellows,

I'm really looking for help with this problem.
Hopefully Clif at Avvid will reply, but I understand that
he has a business to run.

Is there anyone out there who can help me
understand how this amp keying circuit works?

Thanks.

> I find myself in need of some advice again. I have been
> trying to chase down a problem with my Kenwood TS-940/TL-922
> combination.
>
> The problem is this: The amp will unkey after about a minute.
>
> At first it only did it on occasion, now it is getting worse. Originally
> I thought that the amp might be the problem, if only because I have
> had plenty of troubles there. But, I think that it can be ruled out
because
> I can use a shorting plug/switch to key it for a long time with out it
> unkeying. I also tested the amp with another radio for a day, and
> it did not exhibit any problem.
>
> So, I looked at the schematic, and ordered another amp keying relay.
> Installed the relay today, and same problem still exists. I had the
> amp and radio key down, with no drive into the dummy load for
> about 20 minutes with out the relay giving up. But using it on the air
> and it unkeyed in about a minute. After it unkeys the first time, then
> subsequently it will not key, or will key only for short periods. I think
> that the amp relay is working, because I had my finger on it when
> the amp dropped out,and did not feel it release. You can feel the
> little relay catch and release when you put your finger on it.
>
> I'm trying to see how I can troubleshoot this further? Looking
> at the service manual and operators manuals for both the amp
> and radio, I see that the relay should be taking the key line to ground,
> from pin 2 to pin 4 on the remote plug. With my VOM, I cannot see a
> difference between the keyed and unkeyed mode. I did at one time
> see some DC there, which looked to start at about 35 volts and it would
> slowly die down to zero.
>
> I guess the question is: What should I see at the end of my relay control
> cable when the PTT is on? Is there a voltage present? or is it simply
> pulling the signal to ground? The service manual references a 15 vdc
> signal which looks to be routed through the connector. Is this the keying
> voltage for the amp relay? The only other components directly connected
> appears to be a diode and a capacitor. Could one of those be causing this
> problem?
>
> HELP!?! This is starting to drive me batty. If necessary, I'll box it up
and
> send it to you guys... I'm hoping that you will be kind enough to let me
try
> first though, since this rig has been at your shop before, earlier this
year
> and the XYL is not gonna want me to ship it again, although it's still
> cheaper than a new rig!
>
> 73, Gary McAdams, WG7X
>
>
>
>