[Elecraft] [K2] K2/100 - Serial Port Quit Working

[Don Wilhelm]

Bill,

Make certain you have +12 volts on U4 pin 1 and +5 volts on U4 pin 16 
and about -25 volts (-8 to -27 volts) on U4 pin 8.
If those are correct, replace U4 and it should work)

73,
Don W3FPR

On 11/4/2021 3:29 PM, Bill Coleman wrote:
> About 10 days ago, I was having trouble with the K2/100, as it was no longer talking to WSJT-X correctly. I could get the audio running, but it would never contact the radio.
>
> Trying to set up for CQ WW Phone, I had the same trouble with N1MM.
>
> Tried to use the PORT TEST feature by going to the SEC menu, selecting PORT, going into EDIT, and pressing the DISPLAY button. It would say TEST, but I’d see no characters transmitted.
>
> Since I use USB serial adapters, I tried two of them, to no avail. Can’t get a peep out of the K2/100.
>
> Opening up the rig and digging out the scope, if I send characters on the serial port, I see pulse trains on KPA100 U4 - the MAX1406 chip - pin 11 (R3OUT). So, it would appear that characters are reaching the main CPU.
>
> If I put the scope probe on pin 12 (T2IN), it remains locked on ground, never moving, even when I do the PORT TEST.
>
> If I remove the P1 connector from the control board, and put the scope probe on pin 1 of that connector, I DO see pulse trains from the PORT TEST. This indicates to me that the CPU is OK, but something is wrong at the MAX1406 chip in the KPA100.
>
> In addition to not getting a response from the K2, it doesn’t appear to obey commands. If I send RT1; or XT1; it doesn’t turn RIT or XIT on.
>
> I tried using a different main CPU chip (I have one with older firmware), but that doesn’t appear to make a difference. I’m wondering if my problem is a blown MAX1406 chip.
>
> Any recommendations or advice? It’s a big pain to remove the KPA100 board, so I want to make sure what I’m replacing before I go after it.
>
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