TK-860 Backlight Repair

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kwradioguy
Posts: 35
Joined: Tue Oct 24, 2006 7:57 pm
Location: New Britain, PA

TK-860 Backlight Repair

Post by kwradioguy » Mon Oct 13, 2014 12:53 pm

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

KI4LTX
Posts: 10
Joined: Mon Apr 06, 2009 12:14 pm

Re: TK-860 Backlight Repair

Post by KI4LTX » Tue Oct 14, 2014 3:13 pm

There are 4 LEDs, D802-D805; Might also be transistor Q801, or a bad connection at CN801 pin 1.
It is repairable.

kwradioguy
Posts: 35
Joined: Tue Oct 24, 2006 7:57 pm
Location: New Britain, PA

Re: TK-860 Backlight Repair

Post by kwradioguy » Tue Oct 14, 2014 5:49 pm

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?

KI4LTX
Posts: 10
Joined: Mon Apr 06, 2009 12:14 pm

Re: TK-860 Backlight Repair

Post by KI4LTX » Tue Oct 14, 2014 11:02 pm

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

kwradioguy
Posts: 35
Joined: Tue Oct 24, 2006 7:57 pm
Location: New Britain, PA

Re: TK-860 Backlight Repair

Post by kwradioguy » Thu Oct 16, 2014 7:32 am

Thanks John. I will take some measurements.

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