[Kenwood] TM-742A & AD Owners Inquiry

[Gary]

The 741's and 742's (including all the other model variations of the
infamous tribander) all share the same overheating problem especially when
a higher power band module is in the middle of the stack. Your 2m band
module is likely experiencing this and it is slowly damaging the PA brick.
I have serviced at least 50 or so of these and advise you to do two things;

first, limit your transmissions to shorter periods and allow the radio
plenty time to cool off and plenty of air flow over it. The fan mounted on
the back is practically useless. It blows air over the rear heat sinks of
each module but hey, guess what, heat rises! The heat generated by both the
2m and 6m modules is quite high when in QSO and will dissipate into the
module above if sandwiched in this manner not into their rear heatsinks.
Second, relocate the 2m module to the top of the stack. Kenwood often
advises not to do this and has even been known to say it can't work if
relocated, this is not true. Here's the trick; the radio's power cord must
be located on the center module, any module whether it's 10m, 6m, 2m, 220,
440, or 1.2G. The power cord area of the top module is taken up by the fan
connector. I run several tribanders daily in my shack and vehicle with no
problems. It's also important to note the radio works best when mounted
horizontally. If you mount it face up and run it for long periods you will
experience a failure of the control card because all the heat is now
collecting in there. I've even seen one left on and mounted face up, the
plastic control head housing eventually melted onto the metal chassis and
had to be replaced.
With a little care your tribander should work fine just if you help it
dissipate its heat however, the damage may be done and you may need to have
that module serviced or replaced, it's hard to say without bench testing.
73,
Gary


nj9k wrote:

> I have a TM-742A that has a 144 module problem, I think???  When I use
> 146.490 and
> ragchew after a period of talking all of sudden my modulation fades to
> nothing. After I
> unkey the mike all the group lets me know about the fade away and gone.
> I can change
> bands and return and everything is normal again.  This only happens on
> "HIGH POWER".
>
> I connected a swr/power meter inline and it showed no loss of power but
> yet the
> deviation dwindles to nothing.
>
> Has anybody ever had this symptom?  The 144 module is the middle layer
> between a
> 220 module and a 440 module.  Heat? Mic? Power module? Deviation
> component? OR
> Gremlins?
>
> Help!!!
>
> Dick, NJ9K
>
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