[GE] VHF Mastr III question

[n griggs]

Chris thanks for replying.  I was looking at the LBI for a MII and it said that the exciter output was 250mw.  We have a MII amp that we could put in temporarily until we get the MIII amp repaired.  I did get the spare MIII amp powered up at home with 100 watts out.  I set the output via the software to '50' which is about 10 watts out.  So much for following it linerally!  (hihi)  I am letting it cook over the weekend and will put it in place probably Monday.  I did have a wild thought about using a similar transistor (say SD-1428) since the actual output transistors and crosses are scarce - IF that is the problem.  I am hoping that maybe one of the voltage regulators went south or, like you said, a cold solder joint or crack.  I also have put solder wick in place of the jumper.  Always thought that it was crazy to put a piece of rigid metal in a place where it might need to flex.
Neal KC4YCM

--- On Thu, 11/4/10, Chris Boone <Cboone at earthlink.net> wrote:

From: Chris Boone <Cboone at earthlink.net>
Subject: Re: [GE] VHF Mastr III question
To: ge at mailman.qth.net
Date: Thursday, November 4, 2010, 10:51 PM

IIRC the MIII amp is close to the MII....the synth exciter puts out 100mw
like the MII xtal version....
Check the driver stages first..you can check them by putting an insulated
screwdriver on the base and then the collector..if there is no change in PO,
then that stage is suspect....I sometimes ground the base thru a screwdriver
end and see if that affects it....Also measure current draw....the one NOT
pulling the load is of course the bad one...(if you don’t have the GE test
set, you can measure voltage drop across the resistors in the collector
feeds)...
OH BTW check the strap between the final PA and the LP filter...it often
cracks...and the PA sees an open or different load...in MIIs, I put a piece
of solder wick there to allow for the flexing.

You could swap and put a MII amp in there in place to get the rptr back on
the air...

Want any Aerotron UHF rptrs??? Friend of mine who is closing his 2way shop
(has been closing it for 5 years!) has one In pristine shape..asked me if I
wanted it...I passed...I have WAY too many GE parts (20+ MVPs!) Love the
EFJs...have one of those on a UHF rptr being driven by a MVP running just 6
watts out (factory job on the MVP output..a rare bird).

Chris
WB5ITT


> -----Original Message-----
> From: ge-bounces at mailman.qth.net [mailto:ge-bounces at mailman.qth.net]
> On Behalf Of n griggs
> Sent: Thursday, November 04, 2010 8:08 PM
> To: ge at mailman.qth.net
> Subject: [GE] VHF Mastr III question
> 
> Gentlemen (and ladies),
> I am about to plunge head first into the repair of a VHF Mastr III power
> amplifier.  This repeater is currently setup as a ham repeater here in
Georgia
> and, recently, started suffering from poor reception problems.  Upon
arriving
> at the site and putting a power meter on the output, It was discovered
that
> the power level was 6 watts and not the full 100 watts that had been set
back
> in March.  We have a complete spare that is going to be put in place and
my
> question is this:  where should I look first before going full bore at
> troubleshooting this?  Is there a common failure of these amps?  Also, if
the
> finals are toast, is there a good source for them short of contacting
GE/Ma-
> com/Ericsson/who ever they are this week?  RF Parts does not show them.  I
> have repaired GE, Motorola, Johnson, Aerotron (there's and oldie) as well
as
> a few others so there shouldn't be that much of a problem.  I also have
all the
> LBI's for the current modules.   Any
>  assistance is appreciated.
> Thanks
> 
> Neal KC4YCM

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