kenwood troubles

[VE6IVN]

I recently was able to pick up a nice Kenwood ts-940 and it was working great until.......
At a recent contest a few of the guys decided to hook up a amp to the rig now as soon as I turn the rig on it goes into transmit and doesnt come out of it
Anyone else ever have this problem and if so were you able to fix it?

[NQ6U]

For clarification, does it do this even when it's no longer hooked up to the amp?

[VE6IVN]

Yes no amp hooked up and as soon as it powers it goes into transimit

[K7SGJ]

Not having a schematic handy, my first guess would be to look for a problem in the T/R switching circuitry. If it's switched by a relay see if the relay driver is shorted or just biased on all the time. That should get you traveling in the right direction. Use the block diagram to get a general idea of how the switching is done, and then use the schematic to take you to component level.

[VE6IVN]

Thankyou will start looking in that direction

[N8YX]

Which model of amplifier was hooked to the '940, and how was this done - directly, via an isolation device such as an ARB-704?

And the most obvious question: Has the "Send" pushbutton on the leftmost side of the rig somehow become engaged?

[N2CHX]

Not familiar with that radio but maybe there's a jumper on a connector that needs to either be removed or added?

[N2CHX]

A quick Google search suggests maybe a defective Q29.

[NQ6U]

If the amp was an older one, it's possible that the T/R switching ran at too high a voltage for a solid state rig. For instance, on an SB-220 amp, the no-load voltage at the T/R relay jack is well over 100VDC. That could easily fry a transistor on your rig, which was probably designed for around 25V max on the T/R circuit.

[VE6IVN]

Yes I believe it was a old amp and I have started to look at the TR circuitry it definitely shorted something to ground to bring it into tx mode

[N2CHX]

Yes I believe it was a old amp and I have started to look at the TR circuitry it definitely shorted something to ground to bring it into tx mode

From what I read, Q29 is the transistor that would most likely be shorted. Might want to check that out.

[VE6IVN]

KKM ty Looked at q29 its ok so probably the relay next thing to look at also found another one on line bought it so at least I will be back on the air and I will be able to play with this one

[K7SGJ]

KKM ty Looked at q29 its ok so probably the relay next thing to look at also found another one on line bought it so at least I will be back on the air and I will be able to play with this one

When you turn on the radio, can you hear or see the T/R relay engage? If so, something is causing it to pull in. Another thing to try, since you say the relay driver (I assume Q29 is the relay driver as I still haven't looked at a schematic yet) is okay, is to see if it is turned on. Check between the base and emitter and see if there is around .6 volt between them. If so, and the relay is tripping when you apply power, you can assume it is a problem further back.

ETA. If you find the E-B voltage on the relay driver is not always present, and only goes to .6 volt when the radio is put into xmit mode, then perhaps the relay contacts are shorted or stuck. If you do pull the relay out to replace it, that would be a good time take some readings prior to putting the new one in, especially at the relay coil points.

Good luck.

[KG4CGC]

This is better than when I used to watch House.

[KG4NEL]

This is better than when I used to watch House.

Jennifer Morrison as a brunette? Hot yo.

[kb2vxa]

Yeah, I suppose so since she wasn't allowed near any oxygen equipment. I've had some pretty foxy nurses and the one at the physical rehab facility I called Dragon Lady made this look like the back end of a bulldog.