Kenwood TK-860G power button and speaker problem

[Wrench1]

Hello,
I have a Kenwood TK-860G and the power button does not do anything when pushed. The radio is on all the time. I thought it might be the keypad so I used a different keypad off my other TK-860G that I know works still did not work. Also the speaker does not work I swaped out speakers did not change a thing. And I also swaped out the front control/display board when i did this the board thats power works just fine on did not work on the other radio?
The radio does not have the IGN cable installed.

Any thoughts?

 

[ramal121]

The power on sequence in a Kenwood is pretty complicated. If you are sure it's not a problem with the switch itself, troubleshooting that portion can leave you with no hair in short order.

To really check the switch you'll need to find a spot (test point) in the radio labled "PSW". If you measure PSW with a meter, it will show 12 volts as the button is pressed, zero when you release.

If that is good I have only two suggestions. Replace the front panel board (expensive), or the haywire Bubba way is to bridge the switching mosfet and find a way to switch on/off the red power lead (your radio will always be on).

As far as the speaker, plugging a new one onto the board will tell if it went bad or not. The only other switching is at the external speaker jack. Do you have an external speaker you can try? Beyond that, it's the audio PA and board level stuff.

 

[WX9EMS]

Your most likely problem is that Q23 (2SA1641) has failed in the closed position. I have several TK-840 that had this ailment, replaced Q23 and the power button works once again. Q23 should be the biggest transistor on the foil side (bottom) of the board, replace it and you will be back in business again. Contact your local Kenwood dealer and have them order the transistor to keep it to the OEM specs.

 

[ramal121]

Mmmm. Q23 huh? Thanks. Can you explain what that does so I could correlate that to other models?

Shoot, if i wasn't so lazy I'd break out my 840 schematic. LOL thanks...

 

[WX9EMS]

One of the first components in line with the B+ is Q23 (Q4 TK-840, IIRC). It is a high current switching transistor (according to datasheet). I had previously followed through the complicated path you described above and it had lead me to this little bugger. When radio was supposed to be on, the base showed supply volts (13.8V), then when pwr button pressed again, it would show just over 1 volt or so. I removed the suspected offender and checked with my meter and it was defective (closed circuit, should be open). I temporarily replaced the OEM transistor with a TIP36C that I had in the junk drawer and the pwr button functions as it should. Not real sure what makes this component fail, but it seems that every TK-840 I have ever owned has had this problem; but not so much with other Kenwood mobiles. Maybe it is due to heat or over-current issues.

There is a technical description of the power supply and its circuitry in the service manual for those who wish to read more.

This may or may not be the entire fix, but this is what fixed all of my TK-840s with power button problems.

 

[Wrench1]

Thanks for the information. I will open it up and and trace down the PWS circuits. The power button does not bother me that much. I put and new radio in the truck that this one came out of when we started having problems with it. If I could get the audio to work I would put it in one of the skid loarders and have it power with the loarder IGN. I did try and put a pair of head phones in the external speaker jack still had no audio. Any thoughts on what to trace on the audio side.

Thanks Again for all the info so far.