TK-760HG, no audio out

[bob-the-scanner-man]

I've got a TK-760 that has a strange issue. It doesn't put any audio out of the internal speaker or an external speaker plugged into the jack. I tried a different internal speaker but no luck. There are no button beeps and hitting monitor and opening the squelch does nothing.

It transmits fine and when I transmit to it from another radio it lights up and indicates that it is receiving but no audio comes out.

Any ideas? Common issues?

 

[mmckenna]

Is this radio new to you?
Did it ever work correctly?

If it's a radio that recently came into your possession, it's possible it was set up at one time with the KAP-1 Public Address module installed. Installation of that unit involves removing R153 to disconnect the internal/external speaker on the radio and route it to the KAP-1 board.

With the radio facing you, and the cover removed, R153 would be near the back left side of the circuit board. See if it has been removed. R153 is a 0Ω chip resistor. If it's missing, just solder across the two pads where it was.

 

[AK9R]

I've got a TK-760...

The thread title says TK-790HG, but your post says TK-760. Which radio are you asking about?

 

[bob-the-scanner-man]

The thread title says TK-790HG, but your post says TK-760. Which radio are you asking about?

Too late for me to edit it now, but it's a TK-760HG not a TK-790. I made a typo on the title.

 

[bob-the-scanner-man]

Is this radio new to you?
Did it ever work correctly?

If it's a radio that recently came into your possession, it's possible it was set up at one time with the KAP-1 Public Address module installed. Installation of that unit involves removing R153 to disconnect the internal/external speaker on the radio and route it to the KAP-1 board.

With the radio facing you, and the cover removed, R153 would be near the back left side of the circuit board. See if it has been removed. R153 is a 0Ω chip resistor. If it's missing, just solder across the two pads where it was.

This radio is new to me so I'm unsure of its past. I did check for R153 and it IS present on the circuit board.

Any other ideas?

 

[mmckenna]

Is there a 15 pin Molex connector hanging off the back of the radio?

 

[bob-the-scanner-man]

No, no Molex connector. Just power leads and the so239 connector/jumper.

There are also 2 leads going into the radio by the power cable. These are soldered to the 2 tabs on the internal speaker like someone was running an external speaker off the internal speaker somehow.

I tried connecting these to an external speaker during my initial testing and heard nothing.

 

[mmckenna]

There are also 2 leads going into the radio by the power cable. These are soldered to the 2 tabs on the internal speaker like someone was running an external speaker off the internal speaker somehow.

I tried connecting these to an external speaker during my initial testing and heard nothing.

OK, so someone modified it. No telling what happened to it. Could be a damaged audio amp, or something else going on. If there's nothing obvious, it would take hours with the service manual going through it step by step finding where the issue is.

If you've checked all the obvious (minimum/maximum volume, making sure the button tones are on, etc), then it is likely damaged and not an easy fix.

 

[sfd745]

If someone was driving an external speaker off the internal speaker, they probably fried the audio circuit. It also could have been used as a link radio in a VRS setup, pushing audio into another radio. Either way, it sounds like it requires a bench visit (though it's probably not worth the cost).

 

[bob-the-scanner-man]

Sounds like that's what happened. I didn't really spend much at all on it so it's not a big loss. Could probably make more than I paid by selling it for parts on Ebay. Or since it transmits fine use it for TX on a repeater project I've been thinking about doing.

Thanks for the help!

 

[mmckenna]

Yeah, probably your best bet.

You could also get the KCT-19 cable, that would give you easy access to a detector output and you could use it as a data radio/APRS/Packet, etc.
In fact, if you did that and programmed it for 144.390, you could probably sell it to some ham as a dedicated APRS radio and make your money back.

 

[bob-the-scanner-man]

Yeah, probably your best bet.

You could also get the KCT-19 cable, that would give you easy access to a detector output and you could use it as a data radio/APRS/Packet, etc.
In fact, if you did that and programmed it for 144.390, you could probably sell it to some ham as a dedicated APRS radio and make your money back.

That's a good idea actually, the KCT-19s on Ebay are pretty expensive but I might keep an eye out for cheaper one to come along. I've been wanting to set up an APRS station of some kind so this might work for that. Unless it's possible to make a simple one myself since I wouldn't need all of the connections.

 

[mmckenna]

That's a good idea actually, the KCT-19s on Ebay are pretty expensive but I might keep an eye out for cheaper one to come along. I've been wanting to set up an APRS station of some kind so this might work for that. Unless it's possible to make a simple one myself since I wouldn't need all of the connections.

All the pins are on the board, just hard to make connections to them. The KCT-19 just makes it a lot easier.