Kenwood TR-7400A 2 Meter Vintage Radio Repair

[xrunner]

A ham friend of mine asked me to look into the issues with this old Kenwood radio. He got it off Ebay 2 years ago and it's never worked correctly: it had no audio output and would not access the local repeater which requires a tone to get into (it supposedly had a tone board inside set to the correct tone 110.9 Hz).

When I opened it up I quickly found that the speaker had a broken wire, when jumpered it worked and the radio had OK audio, although the speaker really needed to be replaced so I ordered a new one.

The tone board which somebody put in years ago simply did not function, so he agreed to order a new one from Communications Specialists. I wired the new board in a better way than the old one and set the deviation and after a good TX alignment it got into the repeater just fine. The microphone is extremely small and almost looks like a toy. Speaking of which I had to cut back and re-wire both ends due to very bad strain damage over the years. Amazingly the backlight bulb was still working.

I also aligned the RX and proceeded to give it a good cleaning. The chip date codes are 1976. It's interesting how they made the individual LED digit boards in that era. Anyway it's working well and returned to the owner and he's happy. 

[oilburner]

Great pictures, glad to see it running again-  Thanks

G

[Abbas]

Wow, very nice job you did there. I can't help but to notice that the Kenwood TR-7400A look so similar to the Icom IC-255A, except for the second large knob, but everything else looks similar 
BTW, nice Yaesu rig you got there, I have a FT-2900 myself and its built for lifetime 

[xrunner]

Wow, very nice job you did there. I can't help but to notice that the Kenwood TR-7400A look so similar to the Icom IC-255A, except for the second large knob, but everything else looks similar 

Thanks! It's an interesting vintage VHF radio. They designed some things seemingly "backwards" back then. For example to add +5 kHz to the frequency you don't push the button in, you release the button. Same for the high / low power. For high power you release the power button, for low power you push it in. Just the opposite of the way my mind thinks.

BTW, nice Yaesu rig you got there, I have a FT-2900 myself and its built for lifetime 

There are two Yaesu rigs there  - an FT-891 for HF and an FTM100D for VHF which does the digital C4FM. Those are in my living room "mini-shack".

[tautech]

xrunner, do you do a few of these RT repairs ?
Have you seen Defpom's channel....there's a few early on that are quite interesting.
https://www.youtube.com/user/TheDefpom/videos

This one fixing the digital tuning I thought was pretty cool:

[xrunner]

xrunner, do you do a few of these RT repairs ?
Have you seen Defpom's channel....there's a few early on that are quite interesting.

Defpom sounds familiar I may have run across that channel before - I'll check it out tonight thanks.

[kj7e]

The TR7400 had a real front end, with band pass filtering.  Great radio for congested RF areas with no intermod problems the modern wide-band radios have today.

[kf4lhi]

I happen to have the exact same radio which my Father purchased for me when I was 15yr old ( a new 2M operator ). 

xrunner, Would you be open to repeating the same operation of a ‘tune up’ with the addition of the CTCSS Unit.  Largely been used to speak over simplex with modern disability to TX over local repeaters in Aiken SC.

[TheDefpom]

Defpom sounds familiar I may have run across that channel before - I'll check it out tonight thanks.

I was just browsing around and found this thread... you might also know my name from my radiomods.co.nz site which I have had online since 1997.

[xrunner]

I was just browsing around and found this thread... you might also know my name from my radiomods.co.nz site which I have had online since 1997.

Hello! I do know your name. I watched several of your videos on the hp 8904A Multifunction Synthesizer. I got one a while back and wanted to add options and your video helped me do that - thanks! 

[GeoffreyF]

Good job and thanks for the photos!
KC1KNS Lowell, MA

[xrunner]

Answering a PM I received on how to connect the tone board. Posting here for needed attachments.

See the pdf attached which shows how the tone board I used (SS-64) is connected to the TR-7400A. You can use the active filter socket to accept the wiring. It has five pins (see attached screenshot from TR-7400A schematic). Looks like the tone goes into pin1 of that active filter socket. It looks like I simply used three wires from the tone board -

Red: PWR
Black: GND
Yellow: Tone Out

Hope this helps.

[KG9IO]

Yep Thanks! I'll give it a try. 73 Bill KG9IO

[CaptDon]

I owned one of those a very long time ago. Sold it to a fella in New Cumberland Pennsylvania. Mine had a very bizarre after-market scanner feature added externally to it. A very complicated 'add-in' that wasn't done correctly. I had to go over the original kit instructions step by step to catch the errors. Once wired correctly it worked in good order. The front panel knobs had to be set to a specific frequency for the external module to function correctly. Fun times!!