[CQ-Contest] Mk2R+ optocouplers

Kevan Nason knason00 at gmail.com
Tue Jun 8 09:42:14 EDT 2021

Thought I’d try to save some people some frustration.  Apparently,
optocoupler LED’s have a lifetime. As they get old the light generated by
the internal LED’s weakens and can reach the point where it isn’t strong
enough to cause the receiver to register a pulse.

I purchased a MK2R+ from an internet site that was supposedly in perfectly
working condition. Except it wasn’t. During some very helpful exchanges
with microHAM Customer Service (Jozef particularly), they informed me that
due to a supply issue a batch of MK2R+’s had some alternate optocouplers
installed. Although they had the same specifications as their normal chips,
the alternate parts turned out to have a shorter than expected lifetime.
The unit I purchased would connect to microHAM Router, but after a few
minutes the yellow “X” would show indicating it had lost communications to
the MK2R+. It would automatically reconnect after a few seconds or couple
minutes. The longer I tried to operate the MK2R+ the shorter the times
between dropped comms. That indicated a potential thermally related
problem. After 30 minutes of operation the drop might occur every two to
three minutes. Other symptoms included a continually flashing transmit busy
light (until the MK2R+ reset), N1MM+ would be slow to receive rig frequency
information, inability to transmit, N1MM+ might suddenly change SO2R focus
and/or indicated rig mode, and band switching data fed from the MK2R+ would
be delayed or completely lock on a single antenna despite changing bands.
Also, the internal logs that can be activated from within  microHAM router
showed the Mk2R+ was apparently generating an unsolicited PTT signal and
had frequent timeouts during data requests.

Although there are several optocouplers in the unit, only two are used at
high speed and should be replaced. From microHAM:
“Also check what H11L1 optocouplers you have populated in your MK2R+. You
can find two of them in DIP6 package on top board right behind the front
panel POWER button. If they are white than all is OK but if they are black
they can be responsible for issue. White are Fairchild brand, black are
ISOCOM or EVERLIGHT and we found that later deteriorate timing after
several years of use. In this case I recommend you to replace them for
Fairchild brand (now OnSemi but still have F logo on body).”

Mouser had the chips for less than $1 each. It is fairly simple to change
them out. Haven’t used it in a contest yet, but after a three hour static
communication check I had N1MM send CQ into a dummy load for an hour using
a two second repeat. None of the previously noted problems were happening
so it looks like Jozef’s recommendation hit the nail on the head. My unit
is number 478 and made in December 2012. I do not know how long the weaker
chips were used. You can easily see the chips if you pop the cover. They
are on the upper circuit board.

It might be a good idea to proactively check your chips, especially if you
use automatic antenna switching, because this affected how my station

Kevan N4XL

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