Glad to read you solved the problem... you would do well to check the harmonic filter if your pa is the A or plain series.
The late B series pa's were much butter' cheers, skipp > "kk2ed" <[EMAIL PROTECTED]> wrote: > > 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" <skipp025@> > 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 > > > > > >
