Paul Marossy Posted August 29, 2005 Report Share Posted August 29, 2005 This Marshall Series 9000 (9005) stereo power amp that I bought from a friend along with an ADA 2x12 half-stack speaker cab for $100 a couple of weeks ago blew a filter cap the first time I turned it on to check it out. I don't think it had been fired up for several years and had been sitting in a HOT garage for years in what is probably 140-150 deg. F in the summer. So, after having the amp for about 2 weeks, I finally powered it up and checked it out. I was really enjoying the stereo effects that I had going thru the amp for about ten minutes when I heard this noise that sounded exactly like that PSSTTT... sound you hear from that Pixar Animation lamp "popping the ball". Then it was no sound, and smoke pouring out of the amp, and a terrible smell. Took it outside and pulled the bottom cover off to find that one of the LCR filter caps literally blew-up and squirted this oily stuff all over everything. I was laughing because it was actually kind of funny. I was relieved that it was just a filter cap. So, here is a question: After I have replaced all of the filter caps, what should I expect? I'm not sure what else could have possibly been damaged. Anyone else ever have this experience? I'm hoping that all I have to do is replace the filter caps and all will be well... Here is a schematic for the amp: http://www.diyguitarist.com/Schematics/9005Schematic.gif Quote Link to comment Share on other sites More sharing options...
crafty Posted August 30, 2005 Report Share Posted August 30, 2005 I'd check out the various components around the cap to make sure that it failed because of age and not because of over-voltage. Also, try to clean that oily crap off of the boards and components. It's a dielectric, so it probably won't cause a short or anything by itself, but it can dry and attract other things like dust mite excrement that'll cause other failures. Good luck. Oh yeah, you know this, but make sure you've got the new caps soldered in the right direction--you don't want to clean that mess again! Quote Link to comment Share on other sites More sharing options...
VanKirk Posted August 30, 2005 Report Share Posted August 30, 2005 I'd deffinately clean up the cap jizz cause I've seen caps that have leaked and eaten through traces and protective coating. If a visual inspection checks out then you may be just fine but who knows what state it's in. I'd clean up any corrosion or dust bunnies and make sure you have a properly rated fuse before firing it up (maybe a bad choice of words, hehe). I still haven't found a way to put the smoke back in. Let me know if you figure it out. Sorry I don't have a better answer. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted August 30, 2005 Report Share Posted August 30, 2005 If those caps hadn't been powered up in several years, you probably blew through a thin spot in the oxide layer (keeping an electrolytic biased correctly helps keep the oxide dielectric layer nice and thick - if they've been unpowered for a while, the oxide layer tends to thin out, eventually leading to shorts and explosions). Chances are cleaning up the shrapnel and replacing all the electrolytics will completely fix it, but look for charred spots, and be sure to check the rectifier(s) and any resistors in the psu before you crank it back up. I've only had it happen once, and I should have known better, but fortunately nothing else was damaged, and I was gonna have to replace all those caps anyway! Now I use a light bulb in series with the power line when I power something up after it sits for a long time, or else I just go ahead and replace the psu caps first. Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted August 30, 2005 Author Report Share Posted August 30, 2005 Now I use a light bulb in series with the power line when I power something up after it sits for a long time, or else I just go ahead and replace the psu caps first. Yep, I'm building one of these gizmos in the next day or two. I failed to mention that I cleaned out that goop immediately after the cap blew, I didn't want it solidifying and having a hell of a time getting it off later. A visual inspection of both PCBs didn't show anything obvious in terms of damaged components, but I will take a closer look at that tonight. I've got new caps on the way, and hopefully it should be fixed by this weekend. This is what the amp looks like BTW: http://www.diyguitarist.com/GuitarAmps/Marshall9005.htm - it's really in great shape otherwise, and it sounds excellent with my stereo FX unit. Got a question about the light bulb limiter thing. When you use it to power up an amp that hasn't been powered up for a long time, what are you looking for? Are looking for a bright glow in the bulb to indicate a problem inside? Quote Link to comment Share on other sites More sharing options...
lovekraft Posted August 30, 2005 Report Share Posted August 30, 2005 The brighter the bulb glows, the more current the amp is pulling - I use a 25 watt bulb, which should limit the current to a couple hundred mA, and it's pretty bright, but a larger wattage lamp won't be nearly as bright for the same current draw. There's a pretty good article on Geofex, where RG explains (much better than I can) how to use it - look in the Tube Tech section for his Soft Power On adapter. Alternatively, you can do it old school - just take a huge old Variac, and start the amp at about 35 vac, and slowly turn it up to 120vac over the course of several hours, theoretically giving the caps time to "reform". I can't comment, because I never could afford a 200 watt variac, but it makes sense. Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted August 30, 2005 Author Report Share Posted August 30, 2005 Thanks lovecraft. Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted September 1, 2005 Author Report Share Posted September 1, 2005 Last night I changed out the caps and built my light bulb current limiter. Tonight I will test it and the amp out. Here's the cap that blew. Notice that hole at the center. Quote Link to comment Share on other sites More sharing options...
TenderSurrender Posted September 1, 2005 Report Share Posted September 1, 2005 No wonder that made one hell of a mess Good luck with getting this one going dude! ~~ Slain Angel ~~ Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted September 1, 2005 Author Report Share Posted September 1, 2005 I think it will fire right up. I'll test it later on today after I got off work. Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted September 2, 2005 Author Report Share Posted September 2, 2005 My prediction turned out to be right - it lives again! The light bulb limiter worked great and it sounds really good. Apparently the only thing damaged was the filter cap. Maybe I was lucky? Quote Link to comment Share on other sites More sharing options...
TenderSurrender Posted September 2, 2005 Report Share Posted September 2, 2005 Maybe perhaps being an understatement Glad you got it working dude! ~~ Slain Angel ~~ Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted September 2, 2005 Author Report Share Posted September 2, 2005 Glad you got it working dude! Me, too! It's a really nice sounding amp with my stereo effects. Quote Link to comment Share on other sites More sharing options...
TenderSurrender Posted September 2, 2005 Report Share Posted September 2, 2005 Glad you got it working dude! Me, too! It's a really nice sounding amp with my stereo effects. ← Well on that note, Go record some samples n chuck em up dude! I wanna hear what she sounds like... ~~ Slain Angel ~~ Quote Link to comment Share on other sites More sharing options...
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