11 meter modded radio Kenwood 440TS AT Help

[dss56]

I know its a ham radio but modded for 11 meters

I have a Kenwood 440TS AT modded for 11 meters.
I use the MC60A desk preamp mic.

Im wanting to add an echo board/box to the radio and having problems.
3 different echo boards all work on cb radios but not this Kenwood 440.

So I have a small box to put the echo board in.
I added an 8 pin mic jack to the box and a wired 8 pin mic plug straight through pin for pin.

I removed pin 1 audio and put the input echo cable on pin 1 and shield to ground.

The removed wire pin 1 added the the out of the echo board and then ground.

Echo board grnd and 12v+ wired.

turn on echo board and the radio goes crazy audio wise with bad squeal.

I tried 3 different type echo boards and the same problem.

Also tried the kenwood hand mic and same results.

Has anyone tried to add an echo board to the 440ts external.

I tried all kind of ways and still not working.

I take the same boards and put in a 4 pin box wired input and output and power.

tried on a cobra 29ltd and works great.

Am I doing something wrong on the kenwood?

I have installed over 50 echo boards on cb radios with no problem but the Kenwood big problem in Little China LOL

thanks for any help

 

[brandon7861]

It looks like there is a DC voltage on the kenwoods mic pin (going by IF schematic in service manual). Could that DC voltage be affecting the echo board? Have you tried a blocking cap?

 

[Wire Weasel]

Consider simply using an echo mic instead of trying to install a board in the radio? - Not that I think it's going to help much. Those radios have Low AM Audio and not much you can do to punch it up. Made for Sideband.

 

[dss56]

I would use it on ssb Brandon what do you recommend for a blocking cap? I dont have the service manual for this radio just the mic wiring and pin 1 is the audio mic.
Having dc voltage on pin 1 will explain that 3 different echo boards had problems.

Im putting this in a small plastic box as I mentioned not internally in the radio.

thanks

 

[nomadradio]

I would take the power wire for it loose from the mike jack. A low-current variable DC power supply should be on the bench of anyone who does modifications. Power the echo from a separate source and see if that changes anything. If so, power supply filtering is either gone bad in the radio, or needs to be increased on the echo-board side.

73

 

[brandon7861]

I would use it on ssb Brandon what do you recommend for a blocking cap?

Found this online, has a good approach to choosing a cap.

https://www.k5pa.com/Ham%20Radio/Downloads/ICOM%20Mods%20to%20MC-60A%20Mic%20Unit.pdf

 

[bugzilla001]

I would use it on ssb Brandon what do you recommend for a blocking cap? I dont have the service manual for this radio just the mic wiring and pin 1 is the audio mic.
Having dc voltage on pin 1 will explain that 3 different echo boards had problems.

Im putting this in a small plastic box as I mentioned not internally in the radio.

thanks

DSS56: I sent you a pdf of the Kenwood TS440s/at service manual via private message for some reason it wouldn't load here i own one so i have a copy of the manual