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TK-860 Backlight Repair

Posted: Mon Oct 13, 2014 12:53 pm
by kwradioguy
I have a TK-860 on which the orange backlight has failed. I don't have access to a service manual. Before I open it up, can someone tell me:

1) is this repairable w/o replacing the whole display/
2) Is it an LED or a lamp?

Has anyone done this before? Is if fairly easy to repair?

Thank You

Re: TK-860 Backlight Repair

Posted: Tue Oct 14, 2014 3:13 pm
by KI4LTX
There are 4 LEDs, D802-D805; Might also be transistor Q801, or a bad connection at CN801 pin 1.
It is repairable.

Re: TK-860 Backlight Repair

Posted: Tue Oct 14, 2014 5:49 pm
by kwradioguy
Thank you for the info. I take it, other than the LED's, the other parts are on the display board?

It seemed that it lost one or <4 LED's at first. Now all are out.

Do you happen to know the proper voltage levels expected at the B,C,E or Q801 (assuming it is a BJT) during normal operation?

Re: TK-860 Backlight Repair

Posted: Tue Oct 14, 2014 11:02 pm
by KI4LTX
You should have about 3.8VDC at the junction of the collector of Q801 and the anodes of D802 and D804. D803 and D802 are in series, D804 and D805 are in series. So if one went out, you would lose two. The question is why they would go out, unless Q801 is passing too much current.
John
AA4TX

Re: TK-860 Backlight Repair

Posted: Thu Oct 16, 2014 7:32 am
by kwradioguy
Thanks John. I will take some measurements.