Hi Skipp,
Thanks for the suggestion on stealing the parts from a Mitrek. Been there - done that on a number of VHF Micors, but I wasn't sure if the Mitrek used the same devices as the MSR's UHF PA. Anyway, good news. I found the trouble with PA. Evidently, the trace on the combiner substrate, halfway between where the transistor module solders to it and where the trace makes the 90 degree bend towards the three-way combining, had opened up. I'm guessing that since the output path had opened up, the full force of RF from the transistor must have dissipated into the 5.6ohm/1watt balancing resistor. I repaired the trace, and replaced the 1w resistor with a 1/2w for the time being to test the amp. Good as new. The amp is meeting full output specs. Now I just need to pick up a pair of 5.6ohm/1w carbon resistors. Mind as well replace both at the same time to be safe, since the tolerance will most likely be different between one old and one new one. Probably as hard to find nowadays as a 100w Mitrek! 73 Eric KE2D --- In [email protected], "skipp025" <[EMAIL PROTECTED]> wrote: > > A better source... > > Buy the 100 watt UHF Mitrek Mobiles when you can find them. > The PA is a near exact duplicate of the MSR UHF 110 unit. > > After having done it many times... it will still take you > at least 2.5+ hours to do the swap if you have every tool and > trick ready to go. I wouldn't quote less than 3.5 shop hours > to do one. > > The transistors are integrated and sold only as modules each > and there should be at least 3 of the final high power modules > in your PA. The module kits are/were not cheap from Motorhead. > > Good luck and get your specialized tools out. Don't crack the > white substrate material or you can trash that entire section. > > BE SURE TO CHECK THE HARMONIC FILTER... it's probably bad and > in many cases the source of the pa failure. > > cheers, > skipp > > skipp025 at yahoo.com > > > > "kk2ed" <kk2ed@> wrote: > > > > Good Afternoon, > > > > > > I have an MSR2000 UHF 100w PA that died. One of the two resistors that > > balances the three M2502 final transistors fried, and I suspect one or > > more of the three transistors failed. > > > > Anyone repair the 100w UHF PAs before? I tried to find the M2502 from > > RF Parts and a few other parts suppliers, and no luck. I'm going to > > try Motorola parts shortly, but was wondering if anyone knows a > > replacement/equivalent or a better source? > > > > Thanks > > Eric > > KE2D > > >
