[K2] KPA100 - Failure to be recognised - Troubleshooting question

[Bill Coleman-2]

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?

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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[Bill Coleman-2]

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: [hidden email]
Quote: "Boot, you transistorized tormentor! Boot!"
           -- Archibald Asparagus, VeggieTales

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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