Carvin bx500 amp “protect” mode fault repair

PlanBfromOuterSpace

PlanBfromOuterSpace

Nov 13, 2014
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#1
I have a Carvin BX500 amp that I bought used from a fellow TBer a couple of years ago. Very shortly after purchasing it, it starting having the infamous “protect” light fault (when the amp doesn’t turn on and stays in protect mode). Pulling the ribbon cables and spraying contact cleaner would get it working again but never enough to trust it for a gig. Now it seems to only last a few operations before getting the “protect” fault. I’m not looking to start a Carvin amp bashing thread but I would love to hear from those who have had this issue fixed. I read somewhere that the problem could be fixed by soldering the ribbon cable leads directly to the pins on the circuit board. Has anyone had experience with this?
 
#3
I’m not looking to bash on Carvin at all here. I like the amp when it works which is why I want to fix it. I have it mounted in a 112 combo with an 8 ohm 300w Carvin speaker. It is always plugged into this speaker so this fault happens with the 8 ohm load. I have a second 8 ohm 112 cab with the same speaker that I use for extra boom. The protect light fault occurs when one or both speakers are connected and also when they are not connected. If I pull the whole thing apart and spray contact cleaner on the ribbon cable connectors, it will work for a day or two.

The combo cabinet and extra 112 are from a Carvin AG100D Series III acoustic guitar amp. The bx500 fits nicely in this combo cabinet.
 
#4
I should add that even when it is working the protect light sometimes stays on for quite a while before it goes out and the amp starts working. Sometimes it may be 20 or 30 seconds before the protect light goes out.
 
#7
how many ribbons we talking here cause you could hardwire them. seems like there is poor contact somewhere so it could be solder joints or bad ground path. cleaning the cables might help it but it could be getting low voltage because of another problem. sounds like corrosion. or the pin connectors in the ribbons are getting loose. maybe replace the ribbon cables or check ground connections to all the boards its possible they get grounds from board mounted screws and ground points on the chassis. clean and check those as well. if a low voltage is causing this fault check voltage test points according to manufacture. could be a possible bad capacitor or again bad connection causing low voltage. it would be a shame if you spent alot of time doing a hardwire and the problem was elsewhere. or possibly it is corrosion of cables and the spray cleaning isnt enough. they might need to be physically cleaned. the pins on the board and pins within the cables. also if there is high power ceramic resistors getting very hot or any other point getting very hot. this could be causing other components near by to get heated up and desoldering them. or the constant hot/cold cycles are making them have poor solder joints.
 
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#8
I’m pretty sure the problem is related to the connectors on the ribbon cables. Once the amp turns on correctly, it works great so I don’t think it is an overheating component. The problem tends to occur when turning the amp on for the first time after the amp has been sitting for a few days and sometimes when it has been in the cold for a bit (I live near Chicago). There are three ribbon cables and my idea is to just solder the wires directly and lose the plastic plugs but I’d feel a lot better about doing it if someone else has tried this.
bx500.jpg
 
#10
IMO it would be better to have the amp repaired properly than attempt a Neanderthal repair.

As a tech, I would not work on any amp where this sort of repair attempt was done as it can't be disassembled and/or troubleshot as intended and usually the repair attempt causes problems rather than solves them.

I suspect (can not know for sure, of course) that the problem has nothing to do with the interconnect cables but a GOOD technician would be able to diagnose it properly.
 
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#11
agedhorse said:
IMO it would be better to have the amp repaired properly than attempt a Neanderthal repair.

As a tech, I would not work on any amp where this sort of repair attempt was done as it can't be disassembled and/or troubleshot as intended and usually the repair attempt causes problems rather than solves them.

I suspect (can not know for sure, of course) that the problem has nothing to do with the interconnect cables but a GOOD technician would be able to diagnose it properly.
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Absolutely. However if the board has been well lubricated with some kind of spray, all bets are off.

Also might be worth looking into the trade-in offer for a BX-700 if Carvin still does that... Newer design and some more eq and stuff I think.

Before spending money on it, it would certainly be worthwhile to do the test @BassmanPaul mentioned, even though the speaker is rated at 8 ohms nominal. The insulation on the voice cold could be breaking down, especially if it was played hard. Since you have two 8 ohm speakers, if it works with no speaker, maybe try one then the other to see if it is one failed speaker.
 
#12
BadExample said:
Absolutely. However if the board has been well lubricated with some kind of spray, all bets are off.

Also might be worth looking into the trade-in offer for a BX-700 if Carvin still does that... Newer design and some more eq and stuff I think.

Before spending money on it, it would certainly be worthwhile to do the test @BassmanPaul mentioned, even though the speaker is rated at 8 ohms nominal. The insulation on the voice cold could be breaking down, especially if it was played hard. Since you have two 8 ohm speakers, if it works with no speaker, maybe try one then the other to see if it is one failed speaker.
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Nothing worse than trying to repair a failed hack repair attempt, especially when it's "messy" with "cure-all sprays". I just won't service that kind of stuff anymore, not worth the time, hassle and often it's discovered that the damage done makes the amp effectively unrepairable, or inherently unreliable after the repair because of what was further damaged.
 
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#13
I was protected from that with by the book avionics and the company I did instrumentation repairs for had a return to factory spec policy, so it had to be cost effective to unhack. Only one spray bomb and they paid $2000 rather the $5000 for a replacement. They were lucky that was a less sensitive intrument. Had it been the fraction of a nano amp full scale model it would have been a goner.
 
#14
Ugh, just repaired another amp that was "spray-bombed", an otherwise simple inexpensive repair made more costly by this hack attempt. Now I have to go wash my hands again to get rid of the last of the slimy feeling.
 
#16
I purchased this amp used for $250 and now it essentially worthless because it is malfunctioning due to a well-known design flaw with this specific amp. I appreciate the professional amp techs trying to discourage DIY repair and using their services in general but the cost of a certified or factory repair would probably exceed the value of the functioning amp even though the solution is probably a very simple fix. Since the amp is worthless as it is, I don’t see the problem with trying to fix it myself. I am not a “certified” amp tech but I am handy with a soldering iron and I have built several amps and repaired many amps so I don’t appreciate the assumption that this would be a “Neanderthal” or “hack attempt” repair. I am simply asking for advice from someone with knowledge of this specific problem with the Carvin BX500 amp.
 
#17
I didn't hear any naming, we were just discussing possibilities. Also pro amp tech is NOT me! I did component level troubleshooting on circuits similar to audio, but of much great amplification of much smaller signals... and electronic countermeasures :D

Personally, I would try deoxit and plug unplug 15 or 20 times. If that was done, then maybe not. If connectors were sprayed with common contact cleaner, I would attempt to remove that with solvent that's safe for the connectors, then deoxit it (it... it... it... echo :D ). I have a 70's Pioneer stereo amp in my basement ready for it's 4th or 5th deoxit. It gets better every time. Last time was a year ago, so that might be as good as it gets. IIRC, the first treatment lasted a week. In case you are not familiar with it, deoxit lacks the lubricant of contact cleaner and has inhibitors of the corrosion.
 
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#18
PlanBfromOuterSpace said:
I purchased this amp used for $250 and now it essentially worthless because it is malfunctioning due to a well-known design flaw with this specific amp. I appreciate the professional amp techs trying to discourage DIY repair and using their services in general but the cost of a certified or factory repair would probably exceed the value of the functioning amp even though the solution is probably a very simple fix. Since the amp is worthless as it is, I don’t see the problem with trying to fix it myself. I am not a “certified” amp tech but I am handy with a soldering iron and I have built several amps and repaired many amps so I don’t appreciate the assumption that this would be a “Neanderthal” or “hack attempt” repair. I am simply asking for advice from someone with knowledge of this specific problem with the Carvin BX500 amp.
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I stand by my comment that attempting to solder ribbon cables to the pins of the mating connectors is indeed a hack repair of Neanderthal proportions. No different than welding your car's lug nuts to the studs because you feel a vibration and somebody on the internet said it was because of loose lug nuts. Perhaps they missed the actual cause of the problem, like the cat you ran over, or the chunk of missing tire. Without knowing and identifying the actual symptoms and the real cause, ANY repair is just a wild ass guess. Once you do a repair attempt like that, your amp is unlikely repairable by a proper service tech in the future. I don't care how skilled you are as a solderer, that doesn't matter.
 
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#19
looking at the gut shot in a sea of closely, surface mounted components hardwire is little risky. cleaning the cables better or touching up the existing board mounted connectors would probably be more effective. if temperature effects it sounds like corrosion or bad solder joints. possibly damage from being plugged in replugged.
 
#20
What would be better yet is identifying the actual cause rather then guessing! If you don't have the tools to do this, either find somebody who does, or sell is as is and buy a new amp.
 
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