[OZAPRS] MFJ1270 question

[Matthew.Cook at tekelek.com.au]

Damien,

>Any thoughts muchly appreciated - I've given up  on driving into the
office at 2am to fix it ;)

Sounds suspiciously like either a PSU fault or a Hardware fault within the
TNC.   I would pull all of the IC's and clean the sockets with contact
cleaner, the sockets MFJ loaded are renowned for giving problems (if they
had only used machine pin ?:) ).   If there is an intermittant contact
around the memory addressing that will get the poor old Z80 hung up pretty
quick, there is a watchdog circuit which kicks the micro over if it locks
up, looking at the time stamps this may be your problem.

>From there your next suspect is the 7805 regulator up by the front panel.
There is *supposed* to be a spring clip that presses the tab of the 7805
against the front panel for heatsinking.   I have found a number of these
units missing this clip.   The poor 7805's under these circumstances run
blistering hot but dont fail right away, about 6-10 months of continuous
operation is about right before they kick the bucket.   Keep in mind these
units draw 200 @ 12V (~2W) continously so the regulator has a fair amount
of power to dissipate.

That is about it off the top of my head.   I have a circuit somewhere for
these units, you can contact me off list if you need any further help.

73's

Matt
VK5ZMC




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