Beringer powered PA goes into Over Load

[agedhorse]

I see enough totally repairable gear ruined from repair attmpts by hack techs and well intentioned owners that otherwise would have been easily repaired by somebody knowing what they are doing and with the proper tools.

The pad pattern for the 3886 is tight and fragile. Double sided PCB's have plated through holes that are also fragile.

The fault described is not a characteristic fault of paralleled 3886's or one going bad or intermittent.

The cautions have been plainly stated.

 

[bluebird28]

Agedhorse, while I appreciate your advise, you make a lot of assumptions. I have worked on surface mount technology in my hand held Ham radio. I changed out, under my stereo microscope, 2 surface mount resistors the size of a pin head to change the frequency response of the radio. Yes it worked fine when I was done. I used to have a microscope repair business and was into Ham at the time I still maintain my license. I have never lifted a trace in any of my repair work on anything,,,,,,, yet.

Jeffmaxwell, is this a 2 layer board or are there middle layers? I have to talk to the owner of the speaker to see what he is willing to spend on this unit, he replaced it with a newer model and was just looking for a backup if this could be repaired. Do you know how much 4 ea. lm3886's cost?

Thank you all for the replys and support.

 

[Munjibunga]

They look to be about 6 bucks apiece, naked (no PCB).

 

[agedhorse]

Agedhorse, while I appreciate your advise, you make a lot of assumptions. I have worked on surface mount technology in my hand held Ham radio. I changed out, under my stereo microscope, 2 surface mount resistors the size of a pin head to change the frequency response of the radio. Yes it worked fine when I was done. I used to have a microscope repair business and was into Ham at the time I still maintain my license. I have never lifted a trace in any of my repair work on anything,,,,,,, yet.

Jeffmaxwell, is this a 2 layer board or are there middle layers? I have to talk to the owner of the speaker to see what he is willing to spend on this unit, he replaced it with a newer model and was just looking for a backup if this could be repaired. Do you know how much 4 ea. lm3886's cost?

Thank you all for the replys and support.

Just offering advice based on 30 years of seeing folks try to troubleshoot things that they have no idea what they are looking at and having to deliver bad news that their once repairable unit is now ruined. Just because you can follow instructions and change a resistor or two is a pretty far cry from troubleshooting a fault without understanding the circuit (and there are some tricky and non-imtuitive things that are often used in parallel and bridge-parallel applications of these parts to keep them stable under reactive loads).

This advice is not just for you, but others who might contemplate diving into the deep end...

 

[bluebird28]

Wow, I asked my question to see if any experienced individuals could share knowledge and experience and instead of support and suggestions I was handed a load of crap. As Munjibunga stated "harsh man harsh".
I called a couple of Audio repair shops in the area and explained the situation. The owner of one shop stated in very understandable terms "I no longer work on Behringer equipment as I cannot get parts. I explained what was wrong with the unit and he said "Well its now a boat anchor cause it does not work. It sounds like it is one of the power amps, so snip them out, do not try to unsolder them just yet. Once they are cut out turn on the unit and see if it goes into OverLoad, if it does not then you have found your problem, if it does go into over load then it is something else in the circuit and its still a boat anchor. He stated that it is easier to pull the legs out of the circuit board without the body of the chip attached and then suck the solder out so you can replace the LM3886's. Then you can trouble shoot the real problem. Taking the unit in for service cost in the vicinity of $85.00 per hour and time flies when doing diagnostics so a repair bill could be as much as a new powered speaker very easily, which is why I was trying to help a struggling musical family with a new baby. Thank you for you support.

 

[agedhorse]

Sorry, not intended to be harsh at all, just realistic and accurate.

First, diagnostic time does not fly by if you know what you are doing. There are strainght ahead troubleshooting techniques that, along with understanding, experience and test equipment will lead a qualified technician to what the real problem is (in this case I am pretty sure it's NOT the 3886's) and what it will take to repair correctly.

Second, the troubleshooting method you described above is patently absurd IME. That's not how you troubleshoot any amplifier, not if you know what you are doing and don't want to make a smoldering mess out of it.

Third, "parts not available" is also inaccurate, just about every part is available but again, you have to know what you are doing and have real service resources and not just "education by internet". There are, of course, exceptions, but I would have to say that for gear that's less than 15 years old, 99% of all parts that commonly fail are available. You have no way of knowing if a part's not available if you can't correctly identify the parts that have failed and are causing the problem.

Now I do have a problem with folks giving (or sharing) bad advice as there are many others here who are keenly interested in learning and understanding. Bad info and bad advice really gets in the way of the ability to learn good information, and it also carries a certain safety risk that takes some understanding to be aware of. I get enough PM's from forum members asking questions trying to separate fact from fiction thatI know it's a big deal to some of you here. Why learn wrong stuff, how is that helpful to the overall experience?

 

[T-Bird]

Hi.

WOW, talk about being ungrateful.

OP, if You want to diss someone, diss a random nobody hobbyist like me, not one of the most knowledgeable and well respected amp designers around who is willing to help everyone and in this case YOU for FREE.

That one off my chest:
Is this the correct schematic?

Invalid Link Removed

If it is, even a tube-head hobbyist like me who have worked only on a handful of discretes and TDA and STK (anyone remember those babies ) hybrid/integrated amp chips could at least narrow down the problem in about 15 minutes.
Everything is easily separated and that makes block-by-block diagnosing a breeze.

The only "protective circuit" I could find with a quick glance could be defeated in a few seconds as well.

If it's not the schematic on the link above my ramblings may be totally incorrect so, OP, why not reduce us assuming things and help us to help You by providing us with the correct one.

Folks here like to help, sometimes it's just plain impossible to do so .

Regards
Sam

 

[agedhorse]

Hi.

WOW, talk about being ungrateful.

OP, if You want to diss someone, diss a random nobody hobbyist like me, not one of the most knowledgeable and well respected amp designers around who is willing to help everyone and in this case YOU for FREE.

That one off my chest:
Is this the correct schematic?

Invalid Link Removed

If it is, even a tube-head hobbyist like me who have worked only on a handful of discretes and TDA and STK (anyone remember those babies ) hybrid/integrated amp chips could at least narrow down the problem in about 15 minutes.
Everything is easily separated and that makes block-by-block diagnosing a breeze.

The only "protective circuit" I could find with a quick glance could be defeated in a few seconds as well.

If it's not the schematic on the link above my ramblings may be totally incorrect so, OP, why not reduce us assuming things and help us to help You by providing us with the correct one.

Folks here like to help, sometimes it's just plain impossible to do so .

Regards
Sam

Agreed, assuming the correct schematic, a simple straight ahead circuit that's almost trivial to troubleshoot. The protection circuit that you see looks like the LED indicator detector or limiter control detector (can't determine from the tiny screen of my i-device) and probably not for protection. Is there any active over current foldback control to the power supply? (No diag. for PSU)

The opc for the 3886 is quite unique, and doesn't behave in the way of the symptoms described by the OP.

The 3886 is a unique, unusual, but well engineered device with some hidden quirks that require familiarity to recognize. This is why I suggested to the op that he probably didn't realize that he was off base in his assessment. I do not believe the devices are the cause of the problem based on the symptoms (and of course not analyzing the particular unit)

 

[bluebird28]

So what else, in your opinion, would cause the power section to go into overload?

 

[agedhorse]

So what else, in your opinion, would cause the power section to go into overload?

Respectfully, first, you need to determine what is really happening. It may not have anything at all to do with overload. There could be a fault that is causing a loss of signal for example. That's what test equipment and understanding of the circuit allows you to do. What do you have with regard to test equipment? I can think of several pages worth of possible causes.

For example, the symptom your stomach hurts doesn't really tell your doctor much about what could be the problem. It's a symptom, not a diagnosis.

[Disclaimer... if you don't know what you are doing, there are dangerous voltages present inside the amp that can seriously hurt you. ]

 

[bluebird28]

I now only have a Fluke DMM, I sold my Tektronics O scope and all the rest when I sold my Computer Store / repair business of 20 years. I didn't think I would need it any longer. I do have a friend 35 miles away with lots of test equipment but he primarily works on logic stuff. I have worked with CRT's so I am respectful of where I stick things. What is the toroid looking thing in the bottom of the box?

 

[agedhorse]

What is the toroid looking thing in the bottom of the box?

The toroid is the power transformer.

To troubleshoot this, you will need a scope, DMM, signal generator and load resistors at a minimum. It is helpful to understand how the circuit works and what the schematic diagram means.

 

[SirMjac28]

I still think it's the soldering

 

[SirMjac28]

Hi.

WOW, talk about being ungrateful.

OP, if You want to diss someone, diss a random nobody hobbyist like me, not one of the most knowledgeable and well respected amp designers around who is willing to help everyone and in this case YOU for FREE.

That one off my chest:
Is this the correct schematic?

Invalid Link Removed

If it is, even a tube-head hobbyist like me who have worked only on a handful of discretes and TDA and STK (anyone remember those babies ) hybrid/integrated amp chips could at least narrow down the problem in about 15 minutes.
Everything is easily separated and that makes block-by-block diagnosing a breeze.

The only "protective circuit" I could find with a quick glance could be defeated in a few seconds as well.

If it's not the schematic on the link above my ramblings may be totally incorrect so, OP, why not reduce us assuming things and help us to help You by providing us with the correct one.

Folks here like to help, sometimes it's just plain impossible to do so .

Regards
Sam

+10000 And if he had anything to with my M3 Carbine Combo he is a God amongst men.

 

[Munjibunga]

Wow, I asked my question to see if any experienced individuals could share knowledge and experience and instead of support and suggestions I was handed a load of crap. As Munjibunga stated "harsh man harsh".
I called a couple of Audio repair shops in the area and explained the situation. The owner of one shop stated in very understandable terms "I no longer work on Behringer equipment as I cannot get parts. I explained what was wrong with the unit and he said "Well its now a boat anchor cause it does not work. It sounds like it is one of the power amps, so snip them out, do not try to unsolder them just yet. Once they are cut out turn on the unit and see if it goes into OverLoad, if it does not then you have found your problem, if it does go into over load then it is something else in the circuit and its still a boat anchor. He stated that it is easier to pull the legs out of the circuit board without the body of the chip attached and then suck the solder out so you can replace the LM3886's. Then you can trouble shoot the real problem. Taking the unit in for service cost in the vicinity of $85.00 per hour and time flies when doing diagnostics so a repair bill could be as much as a new powered speaker very easily, which is why I was trying to help a struggling musical family with a new baby. Thank you for you support.

I was joking. It may seem harsh, but you should heed Andy's advice. I agree with the shop owner's "boat anchor" analysis. It's a Behringer. People buy them for the low price point, and you get what you pay for. At their price, they weren't made to be repaired, they were made to be thrown away. Here's your own assessment of the situation: "Taking the unit in for service cost in the vicinity of $85.00 per hour and time flies when doing diagnostics so a repair bill could be as much as a new powered speaker very easily ..." which is precisely my point. I fall back on that old chestnut, "Buy once, cry once."

 

[Munjibunga]

The toroid is the power transformer.

To troubleshoot this, you will need a scope, DMM, signal generator and load resistors at a minimum. It is helpful to understand how the circuit works and what the schematic diagram means.

May he borrow yours?

 

[T-Bird]

Hi.

I now only have a Fluke DMM..

Just as agedhorse there said, a DMM won't get You very far, but generally speaking in AF amp diagnostcs, you can test the PS voltage and current draw and the DC offset at output with it.
Very little if anything else really in an AF amp.

Your computer can serve as a signal generator as well as a rudimentary o'scope though.
Since the dual traces suitable for class A/B AF duty run from ~50€, a handy thing to own even if it's not used daily.
IMO anyway

That said, assuming again that the schematic I linked is the correct one, what are the (4?) rail voltages?

Even though "chopstick tapping" is mainly a method for troubleshooting tube amps, it has helped me in finding loose component legs that cause intermittent operation at times.
If You do that, DO NOT USE A PENCIL.
Should be obvious, but You'd be surprised .

Regards
Sam

 

[modulusman]

One of the bands I play with the BL had a pair of those speakers. IIRC he said he had to have both of them repaired and one twice. After it failed the 3rd time it officially became a boat anchor. The other one gets used occasionally as a drum monitor. They do make good boat anchors since they weigh a ton.

 

[agedhorse]

Just a caution when using test equipment with many of the new (especially class d) amps is that the speaker - (speaker minus) terminal often is not ground if its an internal bridge configuration. If you connect this to the scope ground you can essentially short the amp to ground and often destroy a pc based scope instantly. You need a floating, isolated or differential input setup.

Another caution is that the measured waveform voltage may be (a lot) higher than a pc scope can handle without damage.

 

[Kevin aka Kebo]

Holy smoke - Call me when the ambulance arrives... Im smelling a hurt coming on...