On 4/20/07, Neil Baylis wrote: > It was the weakest component when the stressful event happened. LOL... Of course! :-) Why didn't I think of that? (Ha!) > 3. Anyone think "upgrading" either that MB352 or anything else in any > > fashion might make this particular power supply more "bullet-proof"? It > > already doesn't have fused output terminals, and I can foresee a drill, > a > > couple of panel-mount fuse holders, and a slight re-wiring job in its > > future. > > Is it possible that the supply died when you switched it on with a > heavy load? If so, I'd look at limiting the inrush current, by putting > a low valued NTC in series with the primary. I'd probably replace the > electrolytics as well, given that they're at least 10 years old. Understand the inrush current -- no, it died under a heavy load that was increased slowly. (I was testing an RF amplifier and wasn't thinking about it... turned the drive RF up, and up, and up... and if I didn't have other lights on in the ham shack, it would have gotten real dark and quiet! I "confirmed" that the 160W VHF amp does put out 160W of RF, or so... right before the supply croaked... (BIG GRIN) ) I've seen other supplies (especially higher-rated ones) with inrush protection circuits like you mention, and at least a couple of popular supply manufacturers have come up with retrofit kits for their big supplies years ago for that as well... this one always made a nice "clunk" when switched on, from the transformer bouncing the metal case and the capacitors charging up... but I never looked at the inrush current needed to fire it up on anything fast enough to catch it. In general, there's no problem with putting a bigger rectifier there. The reason I ask is that I might have access to a free replacement, if it's the rectifier, but it's likely rated higher than the original in the same packaging. Free is good! Looking over the design, it would just mean that if the supply were over-extended again like I did, something else "downstream" of the rectifier would certainly fail instead, but proper fusing and/or other design changes could eliminate that possibility. Fuses are simple and cheap, and I'm not *usually* as stupid as I was the other night! (Ha!) But there's no point unless you have reason to think that it failed > because it's ratings were exceeded. Another possibility is that it > didn't meet its rated capacity, because it was damaged (e.g. during > manufacture) or because it was an outlier. True. I was going by the manufacturer's recommendation, so I assume they've seen this failure before. See the troubleshooting notes that came with the schematic from them. I assume, but still like to check and confirm, that they know better than I do -- the "common" failure modes of this particular supply. And I know the true meaning of "ass"ume... Other possibilities: Your transformer could be shorted. What are you > going to do then? Yeah, thought about that... will be checking that too. If the transformer's dead, this whole supply only cost about $100 ten years ago... and it's done far more than $10 worth of work a year for that decade, in more than one time zone and more than one home. If I hadn't killed it, it would probably have survived at least another two to five years, even without replacing the electrolytics. Replace those semi-regularly and take better care of it than I did, and it's probably one of those "last forever" supplies. A replacement transformer would probably double the overall cost of the supply over its lifetime, and I'd probably still hunt around for a surplus transformer to fix it for fun, but it'd be okay to replace the whole supply with a similar Astron or other linear supply for a similar price, and/or upgrade. Upgrading is always fun... I have my eye on an Astron RS-60M that would fit nicely in the 19" rack under the ham shack desk! No ham ever turns down newer/bigger toys... but no ham turns down the opportunity to fix anything either. Quite the dilemma, huh? (GRIN) A good solid linear power supply is a requirement for this application since there are weak-signal RF receivers involved. I don't mind the inefficiency compared with fighting RFI noise from the power supplies! (Yes I know about adjustable switching speed switchers, and find they're a nifty "trick" to keep RFI from bothering you on a particular frequency and/or harmonics of that frequency, but feel it's prone to human screwup on my part -- forgetting why I'm hearing "birdies" and or noise -- and linears are RF-quiet and put out reliable power for years unless you do something stupid, like I did.) It's all about opportunity cost, right? It's fun (to me anyway) to fix it, but I know what time I have available to work on it before my opportunity window runs out and I'm officially "wasting time" on it. I also know what it'd cost to replace it completely. If this were a mission-critical supply running something that made money, it'd be a no-brainer -- the supply would be replaced already and I'd be kicking myself for not having a spare around already... but this is just hobby stuff, which can mean the decision about what to do about it will actually be more difficult than work-related decisions. :-) It's hard to quantify, "How much fun is playtime if I spend it fixing the supply vs. doing something else?" Nate -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist