At 07:41 PM 03/10/08, you wrote: >Thanks, >I finally figured this critter out last night. I found the P/N on >that SCR barely readable, but there. It was the 2N681, that Astron >told be it was. Further checking shows it to be 25V/25A. Light! >That's probably why they went to that 50V/65A unit that crosses to nothing! > >I found all I needed at Digi-Key rather than going through Astron. >Hey, when I can't even send email, do they think I am going to order >parts? NOT!
Look at the Astron page at www.repeater-builder.com and you will find a few experiences people have had when communicating with and dealing with Astron... You will also find a few ideas for repairing / rebuilding / modifying an Astron. >Does anyone know what is used for the AMMETER? I want to add V and A >meters. I have a large Ammeter (feed through) but the schematic >shows current being sampled and run through a 500 Ohm pot. Astron uses the same meter for both, just different scales. >I have many 1 milliamp meters. If I can find the right pot and/or >fashion a by-pass wire across the meter then re-scale it that would be nice. I've made shunts from various lengths of wire. One shunt was 20 feet of #18 wire coiled up into a 6-inch circle and taped. >I never have liked the idea of feeding full current through a meter! If they have decent internal shunts that is fine. Look at All Electronics. I've used meters from them. Yes, they are made in various foreign countries, but they work in that application. On a power supply you aren't going to be using the meters as absolute standards (that's what a calibrated DVM is for), just as approximate indicators. Note that the metering calibration resistors may have to be tweaked to have aftermarket meters read right - it all depends on the internal resistance of the meters, and that changes with the manufacturer. Voice of experience - don't let an electrician help you punch the holes for the meters. The so-called three-inch punch is the size of the fittings used to mount a piece of 3-inch conduit into a junction box - the resulting hole is actually about 3 1/2 to 3 3/4 inches. The first time I was young and stupid and ended up having to enlarge the hole further and use a 4 inch meter. >The lightning appears to have gone around the outside of the unit. Lightning goes where it darn well pleases.... >All 8 pass transistors shorted. There are some recommendations on pass transistors on the Astron page. >5 of 8 emitter resistors open. Don't trust the "good" ones. Replace all of them - that way you have 8 identical values (after all , they are supposed to balance the current, and won't if they are not IDENTICAL in resistance). >The MOV blown right off its leads! It's supposed to be sacrificial. Replace it with three as per the Astron page. And use the gap-caps as well. The Astron is built to a price target, and as a result is under-engineered, and over-rated. >Best of all, one mounting on a pass trans appeared to be stripped, no >turning it from outside or inside with pliers. I then realized the trans was >loose! I pried it out and saw the screwhead WELDED to case! Not surprising. Welding is done with high current, and you probably had a current spike in excess of 1,000 amps for a microsecond or three. >The control board, filter caps, rectifier diodes, driver trans, >power transformer >and all else appear to be OK. Change ALL the silicon on the regulator board, including the driver transistor. No sense risking a failure a few months from now for less than $10 in parts. Especially if it's on a hill powering a repeater. >Thanks again for the help All! > >Bruce (PooterWizz) >(CallSign coming soon) >(Tech Test 3-20-08) Mike WA6ILQ
