If the heatsink was very hot, then I would assume that the PA
transistors were working. Obviously, there are better methods to verify
this. But lets say they were working, I would check the jumper between the
PA & filter boards. This is a common failure point on UHF PAs as well. Does
your filter board have tuning capacitors on it? Stations that came from the
factory in a duplex configuration usually had the tunable filter boards.
I've seen where the tuning caps have become problematic as well.
Make sure the balancing resistors are intact on both the input and
output sides of the PA transistors. If one side is charred, then I would
suspect a bad transistor.
73,
Bryan
N3ST
-----Original Message-----
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] Behalf Of Jamey Wright
Sent: Monday, June 06, 2005 7:47 PM
To: repeater-builder@yahoogroups.com
Subject: [Repeater-Builder] Mastr II UHF Station PA Failure
When I went to work this mornining, I noticed that the signal level from the
repeater seemed to be down a little. I contributed it to band conditions
and decided to check it after work. As I was leaving work, I got a phone
call saying the repeater was hung in transmit. This was caused by a power
glitch or brownout from storms causing a controller problem. I arrived at
the site 45 minutes later and found the transmitter keyed. There is a fan
on the cover of the PA that blows across the components but the heat sink
fins were too hot to touch. I shut off the power supply but allowed the fan
to run while I diagnosed the controller problem. The PA was set for 75
watts out. When I checked it, the power was 4 watts and would creep up to 5
watts after 30-45 seconds. This is a Mastr II repeater PA. The number on
the board is PL19D423006G2 Rev C. I didn't look the number up but I assumed
the writing on the PA cover that said 75 watts was correct. Any suggestions
on what and where to check for problems? I don't see any crispy critters on
the board but some of the components are discolored. They look like silver
thay has been exposed to oxygen. Does the UHF PA suffer from the PA output
to filter network jumper problem?
Thanks in advance.
Jamey Wright
KD4SIY
444.325
Wilson Mtn/Oden Ridge, Al
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