BX500 popped and died. Thoughts?

CoffeeBass · #1 08-24-2010, 10:41 PM

Hey all,

Well I bought a BX500 off of a guy a while back and it was great for a few months until the other day. I was using the amp to test some speakers and I plugged in what was essentially a cable with the end cut off and a few seconds later POP! A really loud crack/pop noise and the amp was dead. No power. I opened it up and the fuse was blown. I replaced the fuse (with a fast blow instead of the suggested slow blow) and the new one burnt out immediately. twice. As soon as I turned on the power it went up in a flash.

Called Carvin support. "something is drawing too much power, you'll need to send it in"

Turns out the warrantee is not transferable and also it ended about a month ago.

Anyone out there had any similar problems and could share? Do I need to send it in and spend the $250 (Their flat rate service fee) to have it serviced?

Thanks for looking.,

CoffeeBass

jazzblade · #2 08-24-2010, 10:51 PM

umm.. really dumb question, Why wouldn't you replace the fuse with the correct one? I'm no EE but I would think the starting current MIGHT pop a fuse with the wrong rating. It is possible that the cut off end of the cable that started this mess had a few conductors touching somehow and the amp protected it's self like it should.
Have you tried the correct rated fuse yet? Cheaper then sending it down for them to do it.

CoffeeBass · #3 08-24-2010, 11:46 PM

Jazzblade,

It was the correct rated fuse (5A 250V) it was just not slow blow. This is not a problem. A slow blow fuse is just so that it doesn't blow with momentary musical peaks in the signal. It is fine to replace a slow blow with a fast blow, not the other way around. As far as the wire goes. It was not a wire with the end cut off. It was the equivalent. It was an apparatus that I built to test piezos for building Bill Fitzmaurice cabs. It is a cable that goes to two conacts that I can place a piezo on and complete the circuit testing the piezo. All contact points are isolated and it has worked before no problems. I hooked it up and was about to start testing some when it popped.

I am however going to order the completely right fuse and try it soon. I live on an island so there are not any available here. I think it is a really really long shot, but it is on my list for peace of mind if nothing else.

Cb

Nightlyraider · #4 08-25-2010, 06:45 AM

Slo-Blo fuses are used because the momentary induction surge for the turn on/heat up cycle often will peak above running amperage. Any amplifier with a slo-blo WANTS the ability to draw more then rated; and your fuse "fix" is not doing any good.

You say you hooked the amp up to "essentially a cable with the end cut off". I'm thinking this means you just plugged a nearly complete connection to the amp and then it arced together. Allowing the amp to go from zero to nearly 100% power output instantly. Yep; tech time.

lbwdog · #5 08-25-2010, 07:10 AM

Was it the speaker cable or instrument cable that was cut off? If speaker, you probably had a direct short to the amp's output, which could have fried something. If instrument cable, it probably created a transient peak, which could have blown the fuse.

Try a Slo Blo fuse so that the start up won't blow it.

craig.p · #6 08-25-2010, 12:41 PM

Pure guesswork here, but you could have an early unit. They had problems. This is the danger of buying used gear with a spotty first-run reliability record when there's no outward-facing revision control; you just don't know what you're getting. You might want to call Carvin back, supply them with your unit's serial number, and ask them whether there have been any upgrades since your unit was built. If not, then I'd scrap the thing. If yes, then I'd get it repaired but stop using it for bench work. For bench work you need an amp that can laugh at any impedance thrown at it OR an amp that's so cheap that replacing it every so often won't pose a financial burden. There might be some cheap board-built amps out there that would be fine for testing piezos. Typically all they need are a DC power supply and you're good to go. Something like what's on this page.

BassmanPaul · #7 08-25-2010, 01:19 PM

You don't use a amp to test an unknown speaker system. You use a 9V battery. It'll tell you if your speakers are working, in phase and just about anything else to need to know bEFORE you connect a speaker to an amplifier.

You should send the unit back to Carvin for repair.

Paul

**bass4worship** · #8 08-25-2010, 03:21 PM

Send it in you blew the power transistors.

CoffeeBass · #9 08-25-2010, 06:30 PM

Quote:

Originally Posted by bass4worship

Send it in you blew the power transistors.

Hey all,

Thanks for the replies.
First let me say that I am not testing some unknown speaker system, but checking for phase issues with piezo tweeters. All contacts in the apparatus are isolated and several inches apart. It has worked before and after without problem. I do not think that is the problem. I know this is the facet of this that people will tend to focus on and say "äh here is the problem" I would do the same, but I am as sure as I can be that this is not the problem. Sure enough that I immediately hooked it up to a project amp and finished my work and it was fine.

Bass4worship, how sure are you? There are some good local techs that could replace a part or two, but if they need to search for the problem, nI may as well send it back to Carvin where they have that part down.

I also tried the slow blow fuses and it just popped the breaker in my house before blowing the fuse.

Thanks,

Coffee

5port · #10 08-25-2010, 06:39 PM

My .02 is you should use a non-class D amp for this operation. This is the second BX500 I've seen blown by a speaker mishap (or connector). Class D is not forgiving when it comes to shaky load conditions. I always turn off the BX1500 when changing/disconnecting speakers.

**bass4worship** · #11 08-25-2010, 06:43 PM

Quote:

Originally Posted by CoffeeBass

Bass4worship, how sure are you? There are some good local techs that could replace a part or two, but if they need to search for the problem, nI may as well send it back to Carvin where they have that part down.

I also tried the slow blow fuses and it just popped the breaker in my house before blowing the fuse.

Thanks,

Coffee

had the same problem with one of my other amps so I took it to my local guy and he replace them. It's cost me $185.00

jazzblade · #12 08-25-2010, 06:54 PM

Ah well Coffee, I'm sad that it is in fact terminal. You did all I would do in such circumstances, now the choice of either having it repaired, or used as a door stop. What are your thoughts now? I have had amps blow without a load on it before(usually my fault entirely)but never in such a short time as you explained.

billoetjen · #13 08-25-2010, 06:56 PM

I don't think we're witnessing any mystery here. Dead short in the output stage. No reason to expect it to work any more.

**bass4worship** · #14 08-25-2010, 06:57 PM

Next is the smoke, do it smell burned inside the head?

seamonkey · #15 08-25-2010, 10:35 PM

Carvin use to send out schematics - can you order one?

And then with the power off you can measure things like if an output transistor is shorted.

Most amplifiers have short circuit protection. I'm sure Carvin does. Sounds like just bad luck.

CoffeeBass · #16 08-25-2010, 11:28 PM

No bad smell, no smoke.

thanks all for your thoughts and time, looks like I will be getting my amp into the shop.

Coffee

Munjibunga · #17 08-25-2010, 11:40 PM

Quote:

Originally Posted by 5port

My .02 is you should use a non-class D amp for this operation. This is the second BX500 I've seen blown by a speaker mishap (or connector). Class D is not forgiving when it comes to shaky load conditions. I always turn off the BX1500 when changing/disconnecting speakers.

Yeah, well there aren't a heck of a lot of amps of any topology that are forgiving with a shorted output (0-ohm load).

GregDunn · #18 08-26-2010, 09:58 AM

I think Carvin uses a 3rd-party Class D output module for these amps? If so, they're almost certainly not user-servicable. Carvin would likely just swap the module and send it back to their supplier for repair/replacement of service stock.

BassmanPaul · #19 08-26-2010, 10:14 AM

Quote:

Originally Posted by GregDunn

I think Carvin uses a 3rd-party Class D output module for these amps? If so, they're almost certainly not user-servicable. Carvin would likely just swap the module and send it back to their supplier for repair/replacement of service stock.

I agree. In my mind it's unlikely that a local shop will even look at a class D amp. I know I wouldn't. I'll repeat my suggestion of sending it back to Carvin. What you get back will probably be right up to the latest revision.

Paul

5port · #20 08-26-2010, 03:46 PM

Quote:

Originally Posted by Munjibunga

Yeah, well there aren't a heck of a lot of amps of any topology that are forgiving with a shorted output (0-ohm load).

A tube amp with a transformer output will easily handle momentary shorts. So an old Bogen pos PA amp would work.