PTT issues

[KC2UGV]

So, I've been wracking my head around this rig interface I've been working on. Couldn't get the damned rig to TX no matter what.

So, I finally figured out my interface wasn't the problem. The PTT doesn't work on it. I finally had the duh moment, and tried to just short the two PTT lines together right from the mic jack. no dice.

So, it's a Kenwood TM-241A. This is my first foray into radio troubleshooting, and from what I see in the service manual, basically, the PTT goes from the switch to a 1.7KOhm resistor, then into the CPU.

I've tried a reset, JIC. No dice. However, I'm at a loss to see which of these SMD thingies are the resistor.

Any input?

[N8YX]

Does the rig work with a mic attached?

[KC2UGV]

No dice with the mic attached.

[N8YX]

Good possibility that the CPU is flaky. I may have a spare -241 microprocessor assembly around here somewhere. If I do, you're welcome to it. I need to check out that PK-232 and get it in the mail to you as well...

[N1LAF]

Have to watch the voltage levels from interface to radios. If the input voltage exceeds the VCC to the processor, the processor flakes out.

[KC2UGV]

Ok, update! Leaving it off for a few hours + another rest (The manual details a "jumper" CPU reset seemed to clear it up). So, it's working FB now :) Seems like I know what happened. I think the serial port for this machine has a really, really low "off" state (12V). This biased the transistor, I think, and sent the wrong polarity to the PTT of the thing.. At least, I think that's what happened.

[N8YX]

Ok, update! Leaving it off for a few hours + another rest (The manual details a "jumper" CPU reset seemed to clear it up). So, it's working FB now :) Seems like I know what happened. I think the serial port for this machine has a really, really low "off" state (12V). This biased the transistor, I think, and sent the wrong polarity to the PTT of the thing.. At least, I think that's what happened.

Most of the later generation solid-state rigs I've dealt with keep their PTT lines about 1kohm or so above ground when keyed. You might want to look into using an optoisolator (4N25 or equivalent) as a "buffer" between the two devices.

[N1LAF]

My serial interface (for multiple radios)

http://paulfelgate.com/hamradio/serial/index.html

Works with IC-7000 also

[ad4mg]

Ok, update! Leaving it off for a few hours + another rest (The manual details a "jumper" CPU reset seemed to clear it up). So, it's working FB now :) Seems like I know what happened. I think the serial port for this machine has a really, really low "off" state (12V). This biased the transistor, I think, and sent the wrong polarity to the PTT of the thing.. At least, I think that's what happened.

This is good news! I was wondering if I had sent you a dud. Is the power output up to specs?

[KC2UGV]

Most of the later generation solid-state rigs I've dealt with keep their PTT lines about 1kohm or so above ground when keyed. You might want to look into using an optoisolator (4N25 or equivalent) as a "buffer" between the two devices.

Yeah, next one I build will have an opto isolator in there. Just wanted to get off my keister and finally get this project finished.

My serial interface (for multiple radios)

http://paulfelgate.com/hamradio/serial/index.html

Works with IC-7000 also

Bookmarked Paul :)

This is good news! I was wondering if I had sent you a dud. Is the power output up to specs?

Yeah, no dud. Like I said, I think I reversed the polarity of the PTT input (Courtesy of the -12V low on the serial port). Fixed with a reverse-prevention diode. Looks like the power is up to snuff, be able to tell you for sure come tomorrow when I do the cross-town data xfer :)