There are at least three or four MSR 2000 PA
units available.
Yes, the versions with the ceramic substrate
are very touchy to repair, hacks are not able
to fudge the proper job. Walk away from
any shop that doesn't appear to have first
hand knowledge of methods used for repairing
this type of pa stage.
It's nice to have the hot gas bonder (or
similar) method for repairs, although I know
a limited number of people who can do it with
special soldering systems.
Any strong stress on the substrate will cause it
to fail with hairline cracks. If your PA suffers
from hairline cracks, no fix except new substrates
will (properly) solve the problem long term.
As a general rule...
The mid split high band pa will fail when run
continous at >65% power in the low range. You
derate derate the mid split (range) PA when
using it in the Amateur Band.
The problem is running the PA at reduced
ratings. As a rule of thumb, rf power amplifiers
are best operated within 5% of their rated
values. Running class C rf power amplifiers
at reduced values is not the best option.
> "N9WYS" <[EMAIL PROTECTED]> wrote:
> Chris,
> You say your Motorola shop "soldered across
> the trace"... I guess I need to know HOW
> they did this. We have an MSR2000 UHF machine,
> and our PA has failed twice in about 6 months also.
You need to put two fans in the factory MSR cab,
sucking air from the bottom up and out. Turn the
the UHF PA down to 65 watts output.
> The local tech tried to do the "I'll solder
> across the trace" fix, and it also failed. To have the
> PA repaired properly, we sent it to the Motorola shop (Chicago
> Communications). They have a "hot air" solder system, which is
> apparently needed for this type of repair. I'm told
> the failure was on a board that has a ceramic substrate,
> and if not repaired PROPERLY, it will continue to fail,
> as ours did. Improper heating and/or pressure
> during repair can >>crack the substrate<< and ruin the
> circuit board.
A big time yep... and the power amplifier modules are
not cheap.
> I just got the PA back, and haven't even had a chance
> to get it back on the air yet; nor do I know what
> this repair has cost us.
> Just something you might want to look into.
> Mark - N9WYS
Set the power level down to 75 watts max output and
put at least one fan in place to move the air around.
If you have high duty cycle operation, turn the PA
down even more to 65 watts max output.
cheers
skipp
www.radiowrench.com
skipp025 at yahoo.com
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