Nate, Fallow my instructions you will find where the problem is. my best guess is q6x4,dz2 ziner is shorted if you didn't put stronger fuse. 1. check resistance on C1 is it low ? ohms 2. disconnect or unsolder q6x4,dz2 3. check resistance on C1 again is it sweeping or high? 4. if yes then replace with new component and make sure check all other component too. 5. if you do not want to waist more parts use my old technique instead of fuse use 500watt light bulb. if you got any voltage on output and components are not getting hot now you can put the fuse and test it. sorry there is lot more other methods to do it but I have to go Andre -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf Of Nate Duehr Sent: Friday, April 20, 2007 11:57 AM To: piclist@mit.edu Subject: [EE] A "better" MB352? Okay, I just figured I'd ask... just a fun power supply question or three... I have a linear 13.8 VDC 20A continuous/25A peak power supply that blows input fuses on the 110V AC side as soon as it's powered up. I asked a little too much of it a few nights ago, methinks. :-) My best guess is that the diode bridge rectifier, which is a bog-standard MB352 is toast. I only had time last night to open the case and look for anything "obviously blown"... i.e. "You let the smoke out"... I didn't check it yet. It's been dead for a couple of days, and I've been working too much to even look at it. Of course, I have no problems digging into it and testing it to see if the rectifier is shorted... and replacing it. The manufacturer puts a note on their schematic for troubleshooting that states the rectifier is the likely-to-be-dead component if it's blowing AC input fuses at power-up. The supply is a cheapie Samlex RPS-1220... and looking inside for the first time after using it for almost a decade for various radio projects, etc... I wasn't super impressed with its "Made in China" quality levels... whoever soldered this thing definitely believed in the misguided philosophy of, "The bigger the blob, the better the job!" It's never exhibited any serious ripple or other problems, and just seems to keep chugging along, like linears do... until you stupidly ask of them to give their all by running a high powered radio and 160W VHF amplifier from them... in FM mode. (DOH! What an idiot...) The repair will be simple if that rectifier is the only problem, and there's not much to this supply really. Samlex sent me the schematic, but I don't see a place it's available on the web, so I'll throw it temporarily up on my server for your perusal, if you're interested: http://www.natetech.com/images/powersupply/SEC25-RPS1220.pdf My curiosity is killing me though, and this list is the only group of people that I know that might be able to answer the following: 1. Is the typical failure mode of 4-pin bridge rectifiers shorted or open? I don't do much with them. 2. Anyone want to tackle (just for fun) why it would have been the first component to go "pop" in this particular circuit when too much current was drawn from it? (Note to self... fuse all equipment pulling current from the supply with fuses smaller than the rating of the supply, dummy! Even had 20A fused positions on the PowerPole strip and used the 30A ones. Oops. Dumb dumb dumb.) And here's the one I'm most interested in, being a tinkerer... 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. I guess since I don't work with this stuff every day, I'm wondering if any sturdier "drop-in" replacements for the MB352 out there that might be worth stuffing in the thing, or would that generally be "a bad idea" for other reasons? I'm going to be a little surprised if a component rated for 250V @ 35A blew when the supply input AC line is fused at 5A. Hmm... Any other Tim Taylor style "Rewire it!" modifications anyone thinks might be useful, while I'm in there... always appreciated. :-) It's over ten years old, it's definitely long past time to void the warranty! (GRIN... As if it still had one?) http://www.thinkgeek.com/tshirts/generic/8f52/ Nate -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist