Posted by
Bill Coleman-2 on
Aug 14, 2012; 5:37pm
URL: http://elecraft.85.s1.nabble.com/K2-KPA100-Failure-to-be-recognised-Troubleshooting-question-tp7560222p7561074.html
On Aug 2, 2012, at 11:52 PM, Bill Coleman <
[hidden email]> wrote:
> OK, my K2/100 has been operational since October 2002. Very recently, I started to get some INFO 080 errors, and then the K2 completely failed to recognize the KPA100.
>
> Looking at it on the bench, the Vdd at Pin 1 and 20 of U1 of the KPA100 is about 1 volt. OK, if the PIC doesn't get enough voltage, it is no wonder why the K2 doesn't recognize it.
>
> I removed the U1 chip, and the voltage rises to about 1.1 volts. U3 (the voltage regulator) is warm to the touch, which tells me it is likely current limiting.
>
> Pulled U3 off the board and it tests just fine (although I'll replace it with a new part because now it is rather smoogly). Put an ohmmeter across the 5volt point and ground and I read 13.8 ohms. Hmm. That's in the ballpark.
>
> SO -- it's probably either U4 - the MAX1406 or U6 - the EL5146C chip that's gone bad and is shorted out internally. I don't see any evidence of a solder bridge or flake or other issue. I suppose I'll order some replacements.
>
> Question: Which chip should I remove first? I'm leaning toward the EL5146C, since I was getting some odd-ball power output behavior before the INFO 080 issue raised up. Plus, it has fewer pins than the MAX1406….
>
> Any other suggestions as to why either of these chips might have failed?
OK, since no one answered my original question, I will. Just so we have the records in the archives.
So, to pick up, removing the 78L05 U3 device shows a resistance of about 13.8 ohms -- which is virtually a dead short for the 100 mA device.
Having ordered replacement parts from Elecraft, I decided to put the 78L05 back on the board (I did test it) and try to figure out which chip was bad. Since I suspected U6 - EL5146C, it was first. Rather than trying to desolder it right away, I used a pair of wire cutters to clip pin 7. My theory was, if the 5 Volt line recovered, then U6 is bad -- if the 5 volt line is shorted, then U6 is ok and it's U4 - MAX1406. In the latter case, I could solder pin 7 back down to the pad and not try to pull it off the board.
Well, one thing went wrong and one right. Clipping pin 7 on U6 resulted in the entire pin coming off the chip. Ooops. But, that was ok, because U6 was the bad chip. I clipped U6 off the board with cutters and cleared the soldering holes. Then I put a machine pin socket in place, so I can replace the chip right away whenever Elecraft ships me the parts.
Now to figure out why my KAT100 is not working.
Bill Coleman, AA4LR, PP-ASEL Mail:
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Quote: "Boot, you transistorized tormentor! Boot!"
-- Archibald Asparagus, VeggieTales
Bill Coleman, AA4LR, PP-ASEL Mail:
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Web:
http://boringhamradiopart.blogspot.comQuote: "Not within a thousand years will man ever fly!"
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