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Carvin B800 died... (but came back to life... weird...)

Discussion in 'Amps and Cabs [BG]' started by Trevorus, Mar 7, 2008.


  1. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    Interesting. Just days after reading the thread on the B1500, mine just goes out. There is a resistor on the power board that just burned up BAD. It's extremely hot and making a bad smell. Looks like I'll have to see what Carvin customer service is like.
     
  2. MarkMyWordsXx

    MarkMyWordsXx

    May 17, 2006
    lol good one. like that would ever happen
     
  3. peterbright

    peterbright

    Jan 23, 2007
    On The Bayou
    Good luck
     
  4. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    I think I am buying another GK1001RB-II
     
  5. Oren Hudson

    Oren Hudson

    Dec 25, 2007
    Gastonia, NC
    I bought a Carvin bass amp & head way back in 1967. It was crap. Stayed in the repair shop more than me playing it. Bought a top of the line Carvin bass guitar a couple of years ago. Not as bad as amp, but still crap. What's the deal with them? I'm not going to give them another shot.
     
  6. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    Ok, it gets weirder. It works. I messed with the burned resistor, and broke the casing, and I think I broke the connection inside. Now the amp works again. So looks like I am going to use it like that.

    Anyone care to open their B800 up and tell me what the value of the white ceramic resistor near the power connection is?
     
  7. Stromrider

    Stromrider

    Feb 16, 2008
    CT, USA

    How about a picture?

    Its rare that a resistor dies on its own accord, usually a failure somewhere else causes the resistor to overheat and burn to death but its possible it just up and went short circuit on you. You might try replacing the resistor and watching its, and everything else in the amp, temperature when you power the amp back up.

    If its near the output transistors (the things mounted to a heatsink) you NEED to find out why it blew, and get it fixed, and stop using the amp until you do. Basically, stop using the amp until you find out why that resistor burned up.
     
  8. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    It's connected near the AC in, and touching the connector that hooks to the power switch. I may pop the board out and see what exactly it's connected to to get an idea of it's purpose, because the traces aren't that visible from this side of the PCB. I ran the amp after breaking the casing of the resistor itself, and it ran fine, didn't get hot anywhere, and it's sound was flawless as ever.

    I'll get a pic when I get back home.
     
  9. There's an old saying "you can please all of the people some of the time but you can't please all of the people all of the time". I too took a leap of faith when I bought my first Carvin six string Bass. It was a beautiful instrument as good as any I have ever played. When I wanted a fretless I bought another Carvin six and was again delighted. The fretless developed a small crack in the back so they had me send it back and they built me a new one. I bought yet another six and then put together a bolt on five from Carvin parts. All of them play like a dream. If you did not like the bass you bought why did you not just return it?

    Apart from my basses I have bought lots of Carvin rack gear none of which has ever given me the slightest problem. I don't believe Carvin has any more returns or failures than any other manufacturer. Just look at the number of posts about Ampeg problems on this site.

    Paul

    Paul
     
  10. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    I love Carvin, personally, and no amplifier lasts forever. Mine is working again, and I will ask tech support about it. I'm not sending it back if I don't have to.
     
  11. Your amp has a problem and it WILL need to be repaired. Whatever the power resistor does it has faulted and, as resistors are passive devices, they do not fail by themselves. If your amp is still under warranty Carvin will repair it for you. If not, call them and ask for a copy of the schematic. This will enable you to repair the amp yourself if you have the skills or help a tech to fix it locally. Some times across the life of a product there will be upgrades or modifications made to enhance reliability or to address issues as they are identified. I think you will find that Carvin would incorporate these into your amplifier but a local tech would not.

    Paul
     
  12. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    I've checked it out a bit, and it's part of the power feed to the transformer. It connects between one side of the power switch and the transformer's AC in. It measures at 100.9 ohms or so. With a schematic, I'd be able to tell what exactly it's supposed to be, but for now, it's functioning. If anyone can pop open their B800, I can see exactly what this resistor is supposed to be, and put in a suitable replacement. These wirewound resistors can have flaws in them that would cause an internal short, and subsequent overheating.

    I'm guessing it's probably a 100 ohm, 10-20 watt wirewound reisistor. Without a schematic, I'm not sure of it's purpose exactly, but I would like to have it reliably functional for this weekend.

    BTW, Paul. I'm kind of an electronics nut, and I'm going to be going to school for EE. This is part of why I want to fix it myself, that and I don't want it out for 2 weeks. I've got better things to do than wait on shipping.
     
  13. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    Here's some pics of the damage.

    DSCF3779.

    DSCF3778.

    DSCF3777.
     
  14. Stromrider

    Stromrider

    Feb 16, 2008
    CT, USA
    You need to look at a schematic or trace the board to really find out but i'm guessing thats a "soft-start" resistor. When first powering up a resistor is inline with the mains to limit the current draw. When everything stabilizes in a second or two a relay shorts the resistor and the mains is direct connected to the transformer. Could be the relay failed leaving the resistor to overheat and short.

    If that is the purpose of the resistor than its not a major emergency, but you do need to get it fixed. At start up the transformer and power supply caps look like short circuits to the incoming mains voltage. So for a second or two high current will travel through the transformer stressing components.

    EDIT: 100ohms sounds too high for a softstart resistor value, so the damage caused the value to go up or i'm dead wrong.
     
  15. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    I think you're right on the soft start thing. It has a relay that kicks in mains power, then one that connects the output to the speaker outs. I've got a new set of resistors, and I'll start with the 100 ohms, and if that exhibits any weird behaviour, I may cut it down to 50 ohms. I figure it is operating the same way it did before the resistor acted up...

    Though, now that I think about it, in a soft start PS, if the relay doesn't kick in when it should, that resistor is dissipating a ton of power. That is one thing I noticed about when I first kicked it on when it didn't turn on right. I didn't hear the power on relay. I think that's probably what happened here, the relay didn't kick on for whatever reason. Now, that could belie a different problem, but until it surfaces, it's impossible to diagnose.

    Edit: Put in the new 100 ohm resistor, and it works perfectly. I also located it a bit above that plastic connector so if it melts down again, it won't burn through it. After looking at the old resistor and it's internals, it looks like there was a flaw in the winding. We'll see how this goes.
     
  16. Stromrider

    Stromrider

    Feb 16, 2008
    CT, USA
    Most soft start circuits use 10-50 ohm resistors rated up to 50w, but if your amp has a fast turn on, then it should be okay.
     

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