[Elecraft] #3421 MCU problems?

[Don Wilhelm]

Daniel,

There is a direct connection between the PTT/DIT line at the MCU (pin 30)
and the junction of R1,C1 and the PTT pin on the front panel Mic Config
Header.

But you have not done enough to confirm a bad MCU yet.

Before doing anything else, put a dummy load on the antenna jack, power on
and measure the voltage at Control Board U6 pin 30 - it will normally be
near 5 volts with the dit paddle and PTT lines open.  If it is near zero (or
somewhere between zero and 3 volts) you might have a problem with the MCU -
or a problem elsewhere.

If you find the voltage at zero, pull U6 and again measure the voltage - if
it is still not near 5 volts, check RP4 for good soldering (especially pins
5 and 6) and check for shorts on the line.

If the U6 pin 30 voltage (without the MCU installed)is indeed 5 volts, then
your board wiring is correct and you can then blame the MCU input pin for
your problems.

73,
Don W3FPR

> -----Original Message-----
>
>   Nope - I've already checked both dit/dah lines and neither is
> shorted  to ground. Interestingly - I can insert dahs inbetween
> the dits, but  that doesn't stop the dits from continuing.
>
>   I'm really thinking that a small portion of the MCU may be
> having  trouble since I looked over the schematic design and I
> can't see  anything that might buffer the MCU from the dit/mic
> PTT connection.  Someone please correct me if I am wrong here. It
> appears that there's a  direct connection between the PTT/DIT
> connection on the MCU and the  key/mic connections - and if that
> is the case - the only solution would  be swapping out the MCU.
>
>   Thanks for your quick reply, and hopefully someone can confirm
> my suspicions.
>
>   73,
>   Daniel AA0NI
>
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