> "N9WYS" <[EMAIL PROTECTED]> wrote:
> Gary, Skipp and/or anyone else,
> I'm just curious - where is the failure occurring in
> your PA?
Depends on which model/version you have...
Most PA failures occur in the final transistor
module section. (The expensive parts) The cause
is heat, possibly sourced to the self desoldering
harmonic filter, high duty cycle operation and
or reflected power issues.
> I was also running an MSR2000 (albeit on UHF) and
> I keep getting a failure at the harmonic filter
> on the antenna output side. (Kept melting the
> connection.)
This is a very common problem, there is a fix.
Motorola revised the the pa and the harmonic
filter a few times. The "B" version pa's are
much better than the "A" versions.
I replace the entire harmonic filter with the
late version. Check to see if your unit has
lumped value caps soldered on the filter, or
the equivalent etched value (in the substrate)
caps.
> I've since taken the machine off the air and
> replaced it with a back-up. The backup has
> been happy as a clam for about 5 months,
> whereas the MSR would fail in about 4 - 6
> weeks time.
I spent much of my late 80's era time repairing
MSR A version PA's. Motorhead (motorola) actually
had a depot swap upgrade (to the B version) for
a time.
> If replacing parts in the PA will alleviate my
> troubles, can someone point me in the right
> direction? I'd be willing to scrounge up an old
> UHF Motorola Mitrek and cannibalize it to get
> rid of the headaches I'm suffering now.
A late version mitrek will do the job...
You have to take extra, extra, extra... extra
care not to overheat the modules and ceramic
substrates while removing them from the donor
radio. The general rule when first learning is
to trash one or two substrates before you learn
how to manage the desoldering gun heat properly.
If you hear the ceramic substrate crack one
time, it's probably trash. Same applies to the
micor pa ceramics.
cheers
skipp
skipp025 at yahoo.com
ps: you can email me off the list if you need
a source of used mitrek 110 watt uhf radios.
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