Joe wrote: > I'm slowly going through all my repeater stuff here and have a problem > with the 100 watt UHF PA PL19d424895g32. No output. I checked the > exciter into another identical PA and it works fine. Drive is a little > low, 100mw, but it drives the other identical amp just fine. The bad PA > draws 5 amps when keyed, the power control pot varies this current from > 0-5 amps. No output out of the PA. This was a working repeater that is > being tested on it's original frequency of a 45/1456Mhz split. No parts > look burned or discolored. The straps between the boards look fine, no > cracks. I touched them up with and iron anyway just to check. My first > thought is to check the output of the 40watt stage. > > Any words of wisdom before I tear into this beast? Any ideas? I seems > to remember reading about a UHF PA common problem but can't find it in > any of the reflector archive messages. > > 73, Joe, k1ike
Other's haven't mentioned this, since you're "working" on the PA issues here... but when you get done with that PA, something's not right in an exciter that won't put out at least 200mW. 100 mW sounds like a stage isn't tuned correctly, perhaps. Or you've got something else dying in there. Are any of the slugs bottomed out? You might not really have "gotten there" if you have the wrong side injection and you had to pull it down into the ham band. Interestingly, I think I have a PA that just started doing this exact same thing. It'll be interesting to see if we find the same problem. I won't have it "in hand" and have time for bench work on it for a while, though. First things first, the stupid mounting screw (bottom right, the little ones) somehow got cross-threaded and won't back out... so I'll be enjoying some quality time with a drill and a dremel tool to get the thing off the mountain, before I can even look at it). (Sigh.) I had a VHF go dead early this year that I couldn't see any reason it was dead, until I looked at it from further "away"... then I noticed the hairline crack in the top (and eventually saw where it goes down the sides) of the control IC. Something blew the guts of that IC to smithereens (lightning?) internally and the only external signs of problems was the overpressure from inside the IC case, cracked the side of the IC and split the top to release the pressure, and then it virtually "re-sealed" making it very hard to spot on that flat black casing material. At least it was a "different" failure than usual! Repeaters always keep life interesting... whether you want interesting or not. (GRIN) Nate WY0X
