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Amp smells like burnt marshmallows, won't turn on

Discussion in 'Amp Tech Center' started by bluesmule, Jun 17, 2017.

  1. dsutton24

    dsutton24 Poster Extraordinaire Ad Free Member

    Dec 29, 2010
    Illinois
    No, it doesn't work that way, the only thing before the fuse is the cord, and a bad cord isn't likely to blow a fuse in the amp. The fuse blows from an overload after it, and protects you from burning down your house.

    Something was failing in the amp which caused the 3 amp fuse to blow. The original owner replaced the fuse and it popped, so he put in an oversized fuse. The 10 amp fuse held, and he decided it was best to unload the amp before it quit working altogether. You got it home and whatever was failing finally went pffft! The amp is dead.

    You can't figure out why it won't turn on based on the information and experience you have. Nobody could. Someone who knows how to read a schematic and operate a VOM needs to dig into the amp and figure it out.

    Gutting it and rebuilding it is the most expensive way to go, especially if you have no amp building experience. You're likely to spend way more money than if you bought a new amp, and the probability of the amp working once you're done is small. Read through a few first time build threads and decide whether you're willing to put in that kind of time.
     
  2. BobbyZ

    BobbyZ Doctor of Teleocity

    Jan 12, 2011
    Snellman MN
    Your buddy checked the caps and they were ok ? Did he just look at them?
     
  3. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    Well, let's take a stab at guesstimating a repair bill. Maybe the PT did die. New one is about 120, give or take. A ClassicTone might save a few bucks, a Mercury Magnetics will cost a lot more. That amp is 23 years old, so it needs all the electrolytics replaced anyway. Hmm, 40 or 50 bucks for quality caps like F&T and Nichicon. The rectifier was already found to be bad, so another 5-10 bucks for a new production one.

    Now the great unknown. What, if anything, gave out on the circuit board when the amp quit? And what was causing the original fuse to blow? Filter cap nearing end of life? Power tube starting to go out and draw excessive current? Bias cap failing? That's at least couple of hours of bench time to hook up test gear and investigate/troubleshoot, not to mention the repair time and retest time.

    If you want to take off the back panel and snap a couple of pics to share, that might help folks look for any problems like burnt components or PCB damage. That's perfectly safe, just keep body parts and conductive tools out of the chassis while it's open.
     
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  5. mikeyb

    mikeyb Tele-Meister

    338
    Aug 18, 2014
    Chicago, IL
    Want to find out what's wrong? Use your eyes: Fried part. Use your nose: what stinks?

    I worked with a guy that I'd send to troubleshoot failures like yours. He had a great sense of smell and could find the burnt component every time. I had an early 50's Bassman that would smoke after an hour of playing. Bad cap causing a resistor to burn.
     
  6. Snfoilhat

    Snfoilhat Tele-Meister

    Age:
    36
    173
    Apr 8, 2016
    Oakland, CA
    I think every essential piece of advice to this thread's question has been posted by others (other than more data from the owner about the state of the amp and its fuses and other components), but here is a nugget:

    This amp, like many others, has four+ distinct and to some degree independent circuits, and so to say "it doesn't even turn on" hides some important details.

    Wall electricity passes a switch and a mains fuse and enters the PT and leaves the PT and returns to the wall. On the other side of the PT currents are created in the HV winding which may pass through the rectifier to the power supply, a 5V winding that passes through the rectifier's heater/filaments, and a 6.3V winding that passes through the pilot light and all the other tubes' heater/filaments.

    So it's not so simple to say whether the amp is 'on'. If the light is off, maybe the 6.3V isn't running (and maybe the pilot light is burnt or connection broken). If the rectifier's filaments aren't glowing, probably the 5V isn't running (or maybe the rectifier is mis-seated, or bad). No sound? That won't be clear without more data. Could be HV, could be heaters, because tubes won't conduct no matter how much voltage is on the anodes if there is insufficient heat in in the filaments. Or it's the speaker connection. Or a signal ground. Or... None of these indicators is really good enough without measurements.

    I think it is dangerous to take an indicator (pilot light, tube filament light or temp, speaker hiss/hum), as a 100% sign of whether the amp is 'on'.

    Good luck!
     
  7. Silverface

    Silverface Poster Extraordinaire Ad Free Member

    Age:
    65
    Mar 2, 2003
    Lawndale CA
    If a buddy had to check the filter caps for you I honestly don't think a point-to-point kit would be a great idea. They are not a simple "bolt in and solder a couple of wires" type thing - "kit" is not really a good description. It takes fairly thorough electronics knowledge to install one

    How did he check the caps and determine that "they were fine"? Were the caps the type with date codes, or very current types that haven't been generally available for more than 10 years? Did he unsolder each one and check for leakage?

    There is no way to visually determine caps are "fine". You can, with some, determine the manufacturing date, and a few have only been available for a few years (I'e have to check which ones myself). If not - they *have* to be tested with a good multimeter that can test capacitance/leakage.

    If none of that happened the amp needs to go to a tech.
     
  8. Silverface

    Silverface Poster Extraordinaire Ad Free Member

    Age:
    65
    Mar 2, 2003
    Lawndale CA
    If he's not a tech or have knowledge of electronics/safety which is certainly what it appears from his question - you're advocating unsafe procedures. Nobody without an understanding of basic electronics and amp safety should be inside an amp at all. It exposes them to deadly voltages even when the amp is unplugged.
     
  9. mikeyb

    mikeyb Tele-Meister

    338
    Aug 18, 2014
    Chicago, IL
    I believe that there is a such a warning on the amp forum. Does it have to be repeated on every post?

    The point was that the amp stunk and then failed. Find the stink. I didn't recommend touching anything.

    Even better advice to the original poster would be : "Caveat Emptor!" and now that you've been screwed, take it to a Fender repair depot to get it fixed.
     
  10. dsutton24

    dsutton24 Poster Extraordinaire Ad Free Member

    Dec 29, 2010
    Illinois
    Yes, because here in the internet age inexperienced people get advice like, "Find the stink."
     
    Silverface likes this.
  11. Viejo

    Viejo Tele-Holic

    614
    Feb 12, 2011
    Southern IL
    Are you sure it's not turning on? Check the 3 amp fuse did it blow? It is possible that the just the 6.3 volt filament (tube heater circuit) winding burnt up on the power transformer, then you could have a live amp with no pilot light on. It would appear the amp was off and have very high voltages present in the amp. I had that happen on a Deluxe Reverb once.
     
  12. mikeyb

    mikeyb Tele-Meister

    338
    Aug 18, 2014
    Chicago, IL
    Apparently, his "real" mommy has already warned him, so he took it to his buddy.
     
  13. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    When presented with an amp that comes to me for repair or for sale, the first thing I do is to pull the fuse...or fuses if there are more than one. Since I like older amps, there usually is only one fuse. Buyer or repairperson beware, indeed.
    This amp needs a tech. If your buddy is a real tech, fine....but a real tech would have found the problem when first presented with the amp. So...you need a tech, imho.
    Re: parting it out for sale??? What are you going to sell? The PT is suspect. The circuit is suspect. I suppose the cab and speakers could safely be sold in an ethical manner.
     
  14. BobbyZ

    BobbyZ Doctor of Teleocity

    Jan 12, 2011
    Snellman MN
    Problem with just finding a burnt part, fuse, resister, power transformer, whatever and just replacing it is, something caused it to burn up in the first place.
    Finding the cause and fixing that can be tricky but needs to be done.
     
  15. bluesmule

    bluesmule TDPRI Member

    Age:
    26
    13
    May 30, 2016
    Salt Lake City
    I put a 3A fuse in there and it hasn't blown, so I'm assuming no power is getting to it. My buddy recaps all of his amps, he just doesn't have the time to really go over it, so he just took a quick look. I dropped it off at the tech today, said it would probably be about 3 weeks until he gets to it. Unless my eyes deceive me, the power cable goes straight from the wall into the power switch, and then from the power switch out, which is why I thought there could be a problem with the switch itself, but I wasn't able to test any kind of current in the amp myself, so I can't say that electricity isn't making its way through. The pilot light and the tubes are both cold, but I don't really know what that means. And I would definitely only part out what I could. I'm paying for an unethical sale, why would I turn around and do it myself?
     
  16. Silverface

    Silverface Poster Extraordinaire Ad Free Member

    Age:
    65
    Mar 2, 2003
    Lawndale CA
    Yet those with no experience read recommendations like that and don't *know* not to touch anything. Which is why those warnings are posted.

    And while the OP may read the warning in both threads, some find a thread by a forum search - or even a Google search - and never see the other thread. So yes, it's necessary.

    Exactly.
    Careful pal. You don't want to be insulting. It may be advisable to read the posting rules.
     
  17. Silverface

    Silverface Poster Extraordinaire Ad Free Member

    Age:
    65
    Mar 2, 2003
    Lawndale CA
    How so?

    And yours suggested that an uninformed person perform an unsafe procedure. I was perfectly justified in pointing that out. If you don't think so I suggest you observe give-and-take on this forum a while. The type of comment I made is not uncommon (and not exclusive to me by a long shot).

    Your curriculum vitae is irrelevant when you make suggestions that could harm an uneducated reader. There are many, many people reading this forum who do not have any experience working in amps and part of the responsibility of those who do is ensuring safe information is posted *in the context of the thread or OP's question* (or a sub-question).

    And thousands of dollars aren't at stake here. That information is simply irrelevant, especially when the person who would be doing the "smelling" sone't understand the safety issues! Sorry - experienced folks don't post unsafe suggestions here - and when happens someone will point it out. In this case *more than one* pointed it out.

    Nobody cares about ones' background unless *posted* information and advice presented is consistently good and without harm. Suggesting a post contains incorrect information, factual errrors, a difference of opinion OR presents a danger is not an "insult". You may not like it but since it happens in almost every thread you might want to get used to it.

    Instead of being insulted, making nasty comments or posting a resume (and/or work experience that doesn't apply to the OP's experience level) why don't you do what most do and justify your comments - i.e.explain why others' (again, I wasn't alone) pointing out the safety issue were *incorrect*?

    That's how things work.

    Also - your "if you can't do the work yourself..." comment is off-base IMO. Repairs will probably not cost anywhere near the price of a replacement amp. Are you currently in the amp tech business? If so what would you charge to repair this amp (where the problem is as yet unknown), and what's your estimate of replacement cost? In a simple word - explain.

    As for me - my crystal ball is in the shop, so I don't know what's wrong with the amp and CAN'T give a repair estimate.

    o_O
     
    Last edited: Jun 21, 2017 at 1:20 AM
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  18. beezerboy

    beezerboy Tele-Meister

    Age:
    66
    285
    Sep 7, 2016
    AK
    if I'm looking at the right schematic, there 2 fuses in the power input, F1 @3A, and F7 @4A. these are in series, so if either one goes, there is no power to primary side the transformer. since F7 is internal, I'm guessing it is not the right value either. the light comes on with the heater supply. since its blowing fuses, the problem is either between F1 and the transformer, or the transformer itself. there may be other problems, but thats where to start. my guess is the transformer

    http://el34world.com/charts/Schematics/files/fender/Fender_BASSMAN_59_REV_A.pdf
     
    bluesmule likes this.
  19. Milspec

    Milspec Tele-Holic

    562
    Feb 15, 2016
    Nebraska
    The Bassman reissue is an amp worth repairing. Fender did a good job with that amp and they run what about $900 new? To me, spending $200 to repair the problem is a sound decision.

    It is also clear by all the back-and-forth that we are not going to collectively resolve this issue and it needs to go for professional service. Having a large nose, I am darn good at locating odors myself, but it sounds like there would likely be obvious signs of burnt or over-heated components by the description. Will it be a simple repair is something that I have no way of guessing.

    The only thing that I do know for certain is that nobody should be putting a 10 amp fuse in an amp that calls for a slo-blow 3 amp AND that the previous owner knew there was a problem which he should have disclosed.

    Good luck, hope it turns out to be a simple repair.
     
  20. codamedia

    codamedia Friend of Leo's

    Apr 4, 2009
    Western Canada
    ^^^ This ^^^

    You were conned by the guy selling the amp. Even though you should have checked the fuse before buying the amp, that doesn't leave that person off the hook. I'd be letting the seller know what is happening and expect some money back. Of course... that depends on how long ago the sale took place. If it's been a month or longer I'd just be kicking myself :D
     
  21. BobbyZ

    BobbyZ Doctor of Teleocity

    Jan 12, 2011
    Snellman MN
    I don't know if I'd blame seller for a larger fuse. Could be someone just didn't know any better.
    Stock fuse blows, bigger one doesn't, it's fixed and working fine.
    Obviously us tube amp nerds know that's wrong but that's the way alot of people think.
     
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