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Author Topic: sick tm261  (Read 1597 times)
KE4HYV
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Posts: 2




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« on: March 04, 2013, 08:41:06 AM »

Am trying to set up a 2m station in the house, but my radio won't cooperate! My Kenwood TM261 keeps blowing the fuse when I turn the power on. It worked fine before I put it away a few years ago. I have nothing except a multimeter for troubleshooting. Is it worth sending to Kenwood service? Anyone experience this?
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K8AXW
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Posts: 3723




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« Reply #1 on: March 04, 2013, 09:07:47 AM »

HYV:  I'm not familiar with this rig so let me ask some basic questions.

You DO have the power polarity correct, right?

Take you multimeter and check the resistance between the + and - power lines.  (Disconnected from the power supply of course) If there's zero or extremely low resistance there is a short in the radio.

Open it up and see if there is a diode between the + and - points on the PCB.  If there is a diode it will be right where the Pos/Neg wires connect to the PCB.  If there is, lift one leg of the diode and measure the forward and reverse resistance of the diode.  If it's shorted, you'll need to replace it of course.

If it's shorted it usually means that you applied power with incorrect polarity.  In this case the diode is forward biased and shorts the B+ to ground blowing the fuse and theoretically protects the radio.  Most of the time this shorts this protecting diode.

No diode?  We go from there......
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KA4POL
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Posts: 1962




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« Reply #2 on: March 04, 2013, 10:13:28 PM »

There is indeed a protective diode as AXW described. So it will protect the rig in case of wrong polarity.
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K7KBN
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Posts: 2782




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« Reply #3 on: March 04, 2013, 11:27:13 PM »

Assuming the OP did actually lift one end of the diode and tested it, rather than (as it sounds) just verifying that there is a diode in place, it sounds like the diode may have failed in a shorted condition.
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73
Pat K7KBN
CWO4 USNR Ret.
KE4HYV
Member

Posts: 2




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« Reply #4 on: March 05, 2013, 06:32:37 AM »

D201, Prevents Reverse Current, may be the culprit. Ma110 diode? as soon as I figure out how to get to it. Looks like ...fun...
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KA4POL
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Posts: 1962




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« Reply #5 on: March 05, 2013, 08:38:59 AM »

In my schematic there is a diode D16 right at the power input which shorts the reverse voltage. D16 is a DSA3A1_FK
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