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<DIV><FONT face=Arial size=2>One additional item for Dave...final transistors
are SRF3883 (same as in my 432 amp, and same as came in my FIRST 2 meter amp
according to my records) driven by a single MRF1946.</FONT></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=n1ujs@toast.net href="mailto:n1ujs@toast.net">Bob</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=450@lists.vhfwiki.com
href="mailto:450@lists.vhfwiki.com">144.450 Mailing List</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Friday, November 26, 2010 2:57
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [450] Oh my aching a_ _
!!!!!</DIV>
<DIV><BR></DIV>
<DIV><FONT face=Arial size=2>Have I mentioned lately how much I hate full
disassembly of radio equipment when a repair is necessary?</FONT></DIV>
<DIV><FONT face=Arial size=2>In particular, amplifiers?</FONT></DIV>
<DIV><FONT face=Arial size=2>More specifically, RF Concepts
amplifiers?</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Arrrrrggggggh!!!!!!</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>One SMALL slip up (one badly built jumper) in an
INSTANT created a years worth of headache.......</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Symptoms:</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Initially, the preamp would "click" on, but
REDUCE signals.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Shortly thereafter (after some "keying" and
testing, I no longer heard the relay "click" when engaging the "preamp on"
button.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Present progress......</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Troubleshot by checking voltages and resistances
at various points against a known "good" amp with working preamp.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Lifted a leg of a resistor (last component in
line to relay) and discovered a 13 ohm resistor had thousands of ohms of
resistance. Replaced and attempted to activate relay with direct
voltage....unsuccessful.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Assumption made that said relay no longer
functions. While this may not be the entire problem, further
troubleshooting would be useless without replacement. I have just such a
relay, and in order to replace it the entire board must be
removed....</FONT></DIV>
<DIV><FONT face=Arial size=2>Besides the myriad of screw removals, a few small
wire connections must be desoldered, and (most unfortunately) the transistors
seal to the heatsink must be broken (therefore forever compomised unless you
have enough teflon paste to put back on "just so", which I don't), but "no
bag!" I've done this before. </FONT></DIV>
<DIV><FONT face=Arial size=2>Preparations were made, screw removal began,
then....."oh DAMN!!!!!!!"........</FONT></DIV>
<DIV><FONT face=Arial size=2>For years I had the "high drive" amps.....nothing
in the way of screw removal......this is a LOW drive amp, and one of the
screws is nicely hidden under a capacitor....the type that is a heat sinking
giant metal square, solder down on it underside, sides, and over the top to
the board, as well as a variety of devices...which in and of itself presents
enough heatsinking to prevent removal, but is also "sunk" by the gigantic heat
sink! Not to mention the plethora of sensitive expensive devices in
harms way during such an attempt at extraction.......</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Well anyway, the capacitor was removed (I hope
safely), screws removed, board removed, relay removed from board, new relay
soldered onto board, board replaced, screws in place but not tight.....wires
and caps still to be resoldered.....unknown as to whether anything will be
damaged when done, and what else I will find needing repair.....</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>AAAAAARGGGH!!! Have I mentioned how much my
ass aches?</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>So there you have it.....stopped midway for a
smoke and stress relief break so hopefully I won't destroy anything else today
and can face the rest of this......</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I still need an MRF966 transistor.....I am going
to attempt utilizing a cf300 from a 2 meter spare, but unsure if it is
sufficient for the frequency. We will see.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I hope this has been entertaining for you
all......</FONT></DIV>
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