[450] Oh my aching a_ _ !!!!!

[Bob]

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.
  ----- Original Message ----- 
  From: Bob 
  To: 144.450 Mailing List 
  Sent: Friday, November 26, 2010 2:57 PM
  Subject: [450] Oh my aching a_ _ !!!!!


  Have I mentioned lately how much I hate full disassembly of radio equipment when a repair is necessary?
  In particular, amplifiers?
  More specifically, RF Concepts amplifiers?

  Arrrrrggggggh!!!!!!

  One SMALL slip up (one badly built jumper) in an INSTANT created a years worth of headache.......

  Symptoms:

  Initially, the preamp would "click" on, but REDUCE signals.

  Shortly thereafter (after some "keying" and testing, I no longer heard the relay "click" when engaging the "preamp on" button.


  Present progress......

  Troubleshot by checking voltages and resistances at various points against a known "good" amp with working preamp.

  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.

  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....
  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.  
  Preparations were made, screw removal began, then....."oh DAMN!!!!!!!"........
  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.......

  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.....

  AAAAAARGGGH!!!  Have I mentioned how much my ass aches?

  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......

  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.

  I hope this has been entertaining for you all......


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