Hello,
I only have some experience with a VHF MSR. Skipp sounds like the one to help you with a UHF. I'm not sure what originally failed on my VHF PA, but it sure toasted the board. Burned resistors, capacitors, and the finals. It almost looke like it took a lightning hit, but it failed in the middle of January a couple years ago. Its not impossible to get lighting in the dead of winter in Oregon, but it was a nice CAVU sunny day when it did fail. Gary KB7TRP --- In [email protected], "N9WYS" <[EMAIL PROTECTED]> wrote: > Gary, Skipp and/or anyone else, > > I'm just curious - where is the failure occurring in your PA? I was also > running an MSR2000 (albeit on UHF) and I keep getting a failure at the > harmonic filter on the antenna output side. (Kept melting the connection.) > I've since taken the machine off the air and replaced it with a back-up. > The backup has been happy as a clam for about 5 months, whereas the MSR > would fail in about 4 - 6 weeks time. > > If replacing parts in the PA will alleviate my troubles, can someone point > me in the right direction? I'd be willing to scrounge up an old UHF > Motorola Mitrek and cannibalize it to get rid of the headaches I'm suffering > now. > > -----Original Message----- > From: Gary [mailto:[EMAIL PROTECTED] > Sent: Monday, January 03, 2005 7:55 PM > To: [email protected] > Subject: [Repeater-Builder] Re: MSR2000 PA Problems > > > > --- In [email protected], "skipp025" <[EMAIL PROTECTED]> > wrote: > > > > > "Gary" <[EMAIL PROTECTED]> wrote: > > > About a year and a half ago I replaced the whole board > > > on my VHF MSR2000 110 watt NCD PA. (My PA had more > > > problems than just the transistors) I used the PA board > > > out of a 110 watt mitrek mobile. > > > > Tis' the cost effective way if you have the skills, > > proper tools, bright lights, decafe coffee and knowledge.. > > > > > It took me an afternoon to do it as I recall. I had to > > > remove the power control circuitry and change some > > > values of some resistors on the input side of the mobile > > > PA, but it still works great today with a nice clean output. > > > > The time required seriously depends on the model and > > band of operation. Double the time when dealing with the > > UHF ceramic substrates. > > > > > MSR2000 PA's are notorius for failing, especially the > > > NCD units. > > > > What is an "NCD unit"? > > > > > You could not back the power down enough and still > > > maintain a clean output, no matter how much air you > > > blew on and out of the PA. > > > > ..? > > > > Power reduction is simply done with the pot, if you > > require less than the control circuit will handle, > > simply bypass the final stage. Most RF amplifiers > > work better at the nominal operational values. > > > > > > > The CD units faired a little better, but those > > > darn ham operators could fry > > > them too! Ha! Ha! > > > Gary KB7TRP > > > > Only the Micor style msr pa's seem to be trouble below > > 150Mhz. I've never had a 110 watt vhf intermittent duty > > cycle pa fail when tuned down to 60 watts. Same with > > the high power (semi rare) Paging MSR PA. > > > > The fly in the vhf msr soup is the high split msr > > micor style pa. It's not happy below 150Mhz without > > serious power reduction (or modification). > > > > cheers, > > skipp > > Hi Skipp, > > You are obviously in the business, so needless to say my ignorance > is probably showing. > My MSR has the TLD2532A 110 watt intermittent PA. NCD is more my > terminology (non continuous duty) than anything else. I got into the > habit of refering to an intermittent PA as non continuous duty (NCD) > by hanging around another tech that used it. He was also the one > that filled me in on MSRs' PA history. (however right or wrong the > info was) > > I was running my first PA at 60 watts when it failed. The only thing > different that I'm doing now than before, is I am using fans to blow > air out of the cabinet top side vents, plus a fan blowing across the > PA heat sink fins. Before, I was just blowing accross the heat sink > fins only. I'm not sure how efficient the PA heat sink fan is, > because I had to do some creative engineering to get a fan mounted to > blow up the fins from the bottom. My site owner requires repeaters > to be in cabinets with covers on, and you would know how little room > there is to get a fan mounted to blow on the MSR PA with the front > cover on the cabinet and still do some serious air movement. It does > work and looks somewhat professional. > This repeater was getting heavy use at the first PA failure, but now > not as much use. This may have something to do with its'longevity > now. > > Gary KB7TRP > > > > > > > > > > > Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
