Testing audio boards for the Kenwood, TK-2140 VHF portable.
This model is also capable of LTR trunking, which is not needed for this application, and the poor design of the radio has led to numerous problems with transmit audio, receive audio. I have had to repair about 100 of these radios already. Another weakness in the design, is the 5 volt bus, which ANY momentary short causes the fuse to blow, or the regulators get wiped out first. It's a crap shoot on this.
Another design flaw with this model, are the ceramic filters.
There are no D.C blocking capacitors, which allows current to flow across the poles of the filters, and etch away the plates, causing the receiver to lose sensitivity.
I have posted an image of a filter removed from this model in an earlier post concerning this issue to illustrate the problem visually.
The other problems are the leads to the microphone, speaker and side buttons. The wires are short, frail and break just looking at them!
They are also connected through very tiny two-pin plug/socket assemblies. They are miserable to work with. I supplied close-up images of the audio board's connectors so you can see where the cause of the problems stem from. The card simply plugs in, and is held in place by the main board's pressure, and a small rubber pad.
The board often flops up and down when dropped or the radio is 'abused' more than usual, which causes the connector to flex outward, spreading the contacts, which, over time, causes loss of the audio path, as well as transmit audio, speaker audio, and finally, transmit control. The TX LED stays illuminated after the PTT is released.
In closing, the TK-2140, and all models of this configuration are absolute garbage, and I suggest you buy something better!