I got my hands on a behringer ep 2000 which has a short on all transistors of one channel, every leg of them. Fuse on the rectifier for that channel dies instantly.
What can i start diagnosing? Why would everything be shorted to gnd? How is this possible?
Is it likely to burn 8 transistors all together?
In other threads i see that emitter resistors are mentioned often, in my case they seem fine and test the same as the ones on the working board.
I am going to buy a bunch of fuses to test the rectifier without connecting the amp pcb to it. Could a faulty rectifier damage transistors? Or is it likely something else like misuse or idk what.
Happy to provide pictures and schematics if needed
Thanks for the help.
What can i start diagnosing? Why would everything be shorted to gnd? How is this possible?
Is it likely to burn 8 transistors all together?
In other threads i see that emitter resistors are mentioned often, in my case they seem fine and test the same as the ones on the working board.
I am going to buy a bunch of fuses to test the rectifier without connecting the amp pcb to it. Could a faulty rectifier damage transistors? Or is it likely something else like misuse or idk what.
Happy to provide pictures and schematics if needed
Thanks for the help.
Without any specific knowledge of this unit, and having only glanced at the schematic- Because the output has multiple devices in parallel, one shorted device will prevent you from measuring any others- If you have not already, all of the devices will need to be removed and each tested in isolation. You have had a catastrophic failure somewhere, please don't pop any more fuses as a test strategy. Nasty schematic by the way- gives me a headache. Good luck.
Ahahahahah thanks for the insight! Well behringer isn’t great anyway when it comes to amplifiers but it was almost free and learning diagnostics is the reason i bought it, i will take all of the transistors out and hope just one is dead!
@wparks What could be the cause? Treating it badly and blasting it or some other component failure?
@wparks What could be the cause? Treating it badly and blasting it or some other component failure?
Hoping only one power transistor is dead won’t help in any way. If one is dead, the rest have been driven to within an inch of their lives and how much longer they would have lasted is in question. Replacements must be from the same batch (manufacturing lot) anyway. One batch of NPN and one of PNP. Buy them all at once from any of the major distributors and they’ll all come out of the same tube if their stock is at least full tube quantity.
I tend to keep the working transistors, but they go into “B stock”. For doing one-offs, experiments, troubleshooting. Not to go into a customer’s unit or into one of my own PA racks.
You see techs just replacing the bad one all the time, but there is a very high risk that it will be back with the same problem - even without running it hotter than the blazes of hell and damnation night after night.
I tend to keep the working transistors, but they go into “B stock”. For doing one-offs, experiments, troubleshooting. Not to go into a customer’s unit or into one of my own PA racks.
You see techs just replacing the bad one all the time, but there is a very high risk that it will be back with the same problem - even without running it hotter than the blazes of hell and damnation night after night.
Cool, after removing and individual testing i have one NPN and one PNP which are shorted.
Emitter resistors are marked as R22J (0.22ohm) and test as if they were a short circuit. I guess it is normal since it is such a low value right?
If i try to measure the resistance though i get 1.3, 2.6 and 0.9 Ohm values. Is it because my multimeter only has one decimal? Or would it make sense to replace them as well?
I will order and replace the transistors and test the rectifiers before reconnecting it together.
How would you approach the repair? Simply reconnect it all, plug it in and hope it doesn’t happen again? Or is there any other diagnostics step i need to take?
Thanks a lot!
Emitter resistors are marked as R22J (0.22ohm) and test as if they were a short circuit. I guess it is normal since it is such a low value right?
If i try to measure the resistance though i get 1.3, 2.6 and 0.9 Ohm values. Is it because my multimeter only has one decimal? Or would it make sense to replace them as well?
I will order and replace the transistors and test the rectifiers before reconnecting it together.
How would you approach the repair? Simply reconnect it all, plug it in and hope it doesn’t happen again? Or is there any other diagnostics step i need to take?
Thanks a lot!
Just replacing blown output transistors might not be enough.
Could be something before them has failed and turning on with new outputs might just blow them again.
Use a mains lamp in series with power supply to save your new transistors.
If it powers on and stays bright you still have a fault.
If it flashes once then its probably ok.
Could be something before them has failed and turning on with new outputs might just blow them again.
Use a mains lamp in series with power supply to save your new transistors.
If it powers on and stays bright you still have a fault.
If it flashes once then its probably ok.
The resistor is either ok it’s not. If they measure low ohms they are fine. They can’t short, they can open. Some types can go high in value, but not the ceramic cased wire wound types unless they are blackened from heat. Make sure the driver transistors are ok (replace if unsure - cheap compared to a bank of C5200), and every single component that connects between the bases of the driver transistors. An open circuit failure there is instant death when you turn it back on (quiescent bias current will try to go to infinity). And either use a dim bulb, variac, or both when firing back up to monitor for abnormally high current. Any high current beyond the initial charging of the capacitors needs to be investigated FULLY.
When drivers, resistors, diodes,... all measure well before the output transistors, slowly turn the amp on without output transistors.
If the lamp doesn't light up, good chance you are safe. Measure the DC voltage at the output. Anything below 100mV is fairly good.
Now connect an old speaker and listen if sound comes out. It will not play loud, but if it's playing undistorted (don't cranck up the volume) good chance the amp will be OK.
After that you can mount the outputs.
If the lamp doesn't light up, good chance you are safe. Measure the DC voltage at the output. Anything below 100mV is fairly good.
Now connect an old speaker and listen if sound comes out. It will not play loud, but if it's playing undistorted (don't cranck up the volume) good chance the amp will be OK.
After that you can mount the outputs.
I’m not 100% sure you can run one of these “inside out” amplifiers without outputs. I’d have to study it for a bit first. With a normal EF output stage one can do that (into several hundred ohms). It’s SOP for fixing a Phase Linear. These amps bias like an EF/CFP stage, but do not operate that way for large signals.
One CAN use a single pair of “expendable” outputs for the initial test. It will run well into say 20 ohm load that way indefinitely. It’s a good use of the transistors left over when changing out a whole bank with one bad one.
One CAN use a single pair of “expendable” outputs for the initial test. It will run well into say 20 ohm load that way indefinitely. It’s a good use of the transistors left over when changing out a whole bank with one bad one.
So the suggested method would be putting one of each working transistors back in, connect it to a dim bulb tester and put a 20ohm speaker to see if it works?
The ceramic resistors on the output measure continuity so whats up with them?
The ceramic resistors on the output measure continuity so whats up with them?
Do you mean the emitter resistors of the output transistors? (R59 - R66)
Here's the schematic, it will be easier to follow if you can point to partnumbers.
Here's the schematic, it will be easier to follow if you can point to partnumbers.
Yes exactly them, the 8 that are marked 0E22. They are marked 0.22 ohm, if i take a reading it says 1.2 ohm and they beep if i test for continuity. does it happen because it is such a small value? I tried testing a new 10 ohm resistor i have and it also beeps.
Can I "trust" they are ok if they are perfectly white? is the reason they test at 1.2 ohm due to my cheap multimeter or could it indicate they are faulty?
cheers!
Can I "trust" they are ok if they are perfectly white? is the reason they test at 1.2 ohm due to my cheap multimeter or could it indicate they are faulty?
cheers!
I always replace emitter resistors when a catastrophic failure of output transistors occurs.
Thank you for the info, I will proceed with the advice above and hopefully I fix it and don't have to break your balls any more on this haha
If they test 1.2 ohms and just putting the two test leads together reads 1 ohm they are Probably fine. Low ohms are hard to measure accurately. You can always 4-wire test to be sure. Put it in series with say 8 or 10 ohm on say a 12V supply. Measure the current and voltage drop directly. It requires two meters, as the resistance of the meter and test leads is not negligible and can throw things off between having it in there to measure current and not. A lab supply set to a current compliance of one or two amps will work too. But that is effectively having another meter in there.
Going from 0.22 to 1.2 ohms is highly unlikely. Going to 0.3 or 0.4 ohms is quite possible, although usually associated with burn marks.
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Small update on the situation, although nothing meaningful and more dumb questions..
I replaced the bridge rectifiers as they were measuring weird voltages, tried connecting only one pair of the working transistors and I get a low volume hum when connecting it to a (expendable) speaker, although no music... then i accidentally shorted something, sparked up the room, burned the fuse, got scared and frustrated and gave up for the day... Transistors seem fine though so I just need to replace the fuse.
What are the next steps?
If I hear very low volume hum at the output can I assume this part of the amp is working and that it simply isn't receiving the audio signal?
How would I safely see if the audio signal is reaching them?
Is it an ok idea to probe the driver transistor's base or collector with a speaker driver connected, see if i get sound, then try the same on the power transistors? Would I be causing any problems by doing so?
I also just bought an oscilloscope but still haven't studied how to use it..is it as simple as probing around and seeing if I get a waveform or do I risk damaging it?
Any advice? I'm sorry for asking such basic stuff..
Thanks for babysitting me! 🙂
I replaced the bridge rectifiers as they were measuring weird voltages, tried connecting only one pair of the working transistors and I get a low volume hum when connecting it to a (expendable) speaker, although no music... then i accidentally shorted something, sparked up the room, burned the fuse, got scared and frustrated and gave up for the day... Transistors seem fine though so I just need to replace the fuse.
What are the next steps?
If I hear very low volume hum at the output can I assume this part of the amp is working and that it simply isn't receiving the audio signal?
How would I safely see if the audio signal is reaching them?
Is it an ok idea to probe the driver transistor's base or collector with a speaker driver connected, see if i get sound, then try the same on the power transistors? Would I be causing any problems by doing so?
I also just bought an oscilloscope but still haven't studied how to use it..is it as simple as probing around and seeing if I get a waveform or do I risk damaging it?
Any advice? I'm sorry for asking such basic stuff..
Thanks for babysitting me! 🙂
A low volume hum is usually a bad sign. The amp inherently has fairly high ripple rejection, so hearing a low hum is usually a sign of something somewhere drawing too much current causing excessive ripple.
Never go probing around with a speaker connected. Use a dummy load that’s maybe a few hundred ohms. I get things working well before connecting even an expendable speaker. If you want to hear large signal operation put a 500 to 1k power resistor in series with a speaker. If it slams the output with DC it’s not the end of the world, and you can listen at clipping (to assess the amp’s behavior while doing so) without going deaf. You can operate with a dim bulb limiter that way to be sure it won’t do something dumb as the supply voltage falls. You take it in stages - it has to pass each progressively more difficult functional test before moving on to the next one.
The rectifiers will measure weird voltages in operation with signal. The power supply is floating with respect to ground. It’s a weird design that takes some getting used to.
Never go probing around with a speaker connected. Use a dummy load that’s maybe a few hundred ohms. I get things working well before connecting even an expendable speaker. If you want to hear large signal operation put a 500 to 1k power resistor in series with a speaker. If it slams the output with DC it’s not the end of the world, and you can listen at clipping (to assess the amp’s behavior while doing so) without going deaf. You can operate with a dim bulb limiter that way to be sure it won’t do something dumb as the supply voltage falls. You take it in stages - it has to pass each progressively more difficult functional test before moving on to the next one.
The rectifiers will measure weird voltages in operation with signal. The power supply is floating with respect to ground. It’s a weird design that takes some getting used to.
Thanks for the advice @wg_ski !
Do you know of any book or resource or method I could study regarding the theory and steps of diagnostics/repair for this kind of stuff (audio related or not) wthout having to get an engineering degree?
I'm finding it very hard to grasp the how's and the why's of circuits ...as a Diy-er as my electrical knowledge stops after basic high school ohm's law stuff and while I'm slowly starting to understand how amps work by asking, reading, making and breaking I get stuck all the time on silly stuff which someone with some knowledge and experience like you could answer in an instant.
I am super passionate and love the outcomes of what can be done with audio devices but I'm also a very visual person, so not being able to physically see voltages and currents is annoying even though I understand what is supposed to happen on paper and ignorance is driving me crazy.
Cheers,
Liam
Do you know of any book or resource or method I could study regarding the theory and steps of diagnostics/repair for this kind of stuff (audio related or not) wthout having to get an engineering degree?
I'm finding it very hard to grasp the how's and the why's of circuits ...as a Diy-er as my electrical knowledge stops after basic high school ohm's law stuff and while I'm slowly starting to understand how amps work by asking, reading, making and breaking I get stuck all the time on silly stuff which someone with some knowledge and experience like you could answer in an instant.
I am super passionate and love the outcomes of what can be done with audio devices but I'm also a very visual person, so not being able to physically see voltages and currents is annoying even though I understand what is supposed to happen on paper and ignorance is driving me crazy.
Cheers,
Liam
What was the dim bulb series the AC input doing when you made the great big spark? Be especially careful on op amps. The output pins are right next to the power pins and shorting the two will inevitably blow the output. All op amp inputs and output should be same DC voltage if they are working okay.
I tned to use a trash speaker most of the time after DC is gone on the output. However I protect it from DC with series electrolytic capacitors. >3000 uF minus to minus will do. Old electrolytics that are subject to fail any time are what I use. Use ones with voltage rating>the power supply rating of course.
Community college electronics texts are useful for basic understanding. I picked up Electronic Devices and Circuit Theory Boylestad & Nashelsky for $2 at Salvation Army. One by Floyd was better but was stolen along with every part I owned, all the sound equipment, musical instruments, 2200 LP & 200 CD. Electronic text books required by the physics department were generally not useful for practical work. Except kirchoff's laws and vector algebra are useful for tone control design and speaker crossovers.
Be careful probing around. I find a Pamona grabber or Que-ball is more precise for probing than a bare meter probe. Scope probes should have the ground removed for audio work. Grounding through a lead to the amp speaker return is okay for audio, but not for RF. Do not use two hands, voltage >24 across the 2 hands can stop your heart. Wear no rings or jewelry hands wrists or neck. Wear safety glasses with power on or desoldering, parts can explode and solder splashed in the eyes can blind you.
Generally fix DC voltage before trying music or AC source. With input shorted, speaker output <100 mv, Vbe of transistors 0.6-0.7 v unless turned off LED drivers or relay drivers. Vce of transistors somewhere in the middle of 2 power rails, symmetric on plus and minus sides. Voltage across zener diodes = datasheet voltage. Voltage across resistors low enough to not exceed the power rating. Voltage across capacitors not zero. I usually fix amps without using a scope, although they are useful for checking for ultrasonic oscillation. An analog VOM on 50 vac scale back end or 2 vac scale front end is useful. Block negative probe with .047 uf capacitor, they read AC voltage on DC scale without. Analog VOM shows AC at a point and you don't hear anything, possibly oscillation. Megahertz will pass a 390 pf blocking capacitor, music will not.
This amp has a clipping compressor to prevent blowup of speakers when a clipped signal is entered. The 13700.
Used transistors from a blown amp can be checked out of circuit. First Vbe Vce =600 forwards on diode scale. +9999 or ---- backwards. Passes that, Put Vce 12 v through a 47000 resistor and current scale of DVM. +c to e npn, - c to e pnp. Current 2 microamp or less, okay. Current 250 microamp, this transistor is trash.
Happy hunting.
I tned to use a trash speaker most of the time after DC is gone on the output. However I protect it from DC with series electrolytic capacitors. >3000 uF minus to minus will do. Old electrolytics that are subject to fail any time are what I use. Use ones with voltage rating>the power supply rating of course.
Community college electronics texts are useful for basic understanding. I picked up Electronic Devices and Circuit Theory Boylestad & Nashelsky for $2 at Salvation Army. One by Floyd was better but was stolen along with every part I owned, all the sound equipment, musical instruments, 2200 LP & 200 CD. Electronic text books required by the physics department were generally not useful for practical work. Except kirchoff's laws and vector algebra are useful for tone control design and speaker crossovers.
Be careful probing around. I find a Pamona grabber or Que-ball is more precise for probing than a bare meter probe. Scope probes should have the ground removed for audio work. Grounding through a lead to the amp speaker return is okay for audio, but not for RF. Do not use two hands, voltage >24 across the 2 hands can stop your heart. Wear no rings or jewelry hands wrists or neck. Wear safety glasses with power on or desoldering, parts can explode and solder splashed in the eyes can blind you.
Generally fix DC voltage before trying music or AC source. With input shorted, speaker output <100 mv, Vbe of transistors 0.6-0.7 v unless turned off LED drivers or relay drivers. Vce of transistors somewhere in the middle of 2 power rails, symmetric on plus and minus sides. Voltage across zener diodes = datasheet voltage. Voltage across resistors low enough to not exceed the power rating. Voltage across capacitors not zero. I usually fix amps without using a scope, although they are useful for checking for ultrasonic oscillation. An analog VOM on 50 vac scale back end or 2 vac scale front end is useful. Block negative probe with .047 uf capacitor, they read AC voltage on DC scale without. Analog VOM shows AC at a point and you don't hear anything, possibly oscillation. Megahertz will pass a 390 pf blocking capacitor, music will not.
This amp has a clipping compressor to prevent blowup of speakers when a clipped signal is entered. The 13700.
Used transistors from a blown amp can be checked out of circuit. First Vbe Vce =600 forwards on diode scale. +9999 or ---- backwards. Passes that, Put Vce 12 v through a 47000 resistor and current scale of DVM. +c to e npn, - c to e pnp. Current 2 microamp or less, okay. Current 250 microamp, this transistor is trash.
Happy hunting.
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