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Active Speaker Amplifier Capacitance issue
Old 2 weeks ago
  #1
Active Speaker Amplifier Capacitance issue

I don't know or cant figure out why this QSC HPR152i active loud speaker is doing what its doing. So when I opened it up I had noticed that a 63v 6800uf capacitor had puked its guts all over. Figured it was just a matter of replacing the component. So i did that. but then I got a smokeshow. After that i tried a fresh cap. this time i used a variable voltage regulator. The speaker does work fine with the voltage regulator but it will just start smoking when ever it sees anything above 96vac. I was just wondering what the problem is and if there was a way to somehow lower the voltage internally, perhaps a resistor off of the +110v wire coming from the transformer? Or just get a bigger capacitor? Or is there a whole different issue going on?
Attached Thumbnails
Active Speaker Amplifier Capacitance issue-16310454507557906406915434622890.jpg   Active Speaker Amplifier Capacitance issue-20210907_144748.jpg   Active Speaker Amplifier Capacitance issue-20210907_144919.jpg   Active Speaker Amplifier Capacitance issue-20210907_145118.jpg  
Old 2 weeks ago
  #2
Gear Addict
 
Some other component in either the power supply or the amplifier has shorted out , impossible to say what it could be without seeing a schematic so you probably should get this thing to a repair shop.
Old 2 weeks ago
  #3
Repair shop is out of the question..... my question now is what does the (+)( -) voltages written on the PCB signify? i noticed that theres 2 wires coming off transformer, red and blue the red is +110v and is connected directly to the power switch. the blue -110v and was not connected but capped. Why is there an option to use one or the other?

I also considered the shorting, so i just de-gunked the PCB. There was electrolytic juice leftover from the capicitor popping its top.
And as for shorting what other components would allow the whole unit to work just fine between about 58vac and 96vac. But then above that range cause the capicitor to blow.
Attached Thumbnails
Active Speaker Amplifier Capacitance issue-20210907_171752.jpg  
Old 2 weeks ago
  #4
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JohnRoberts's Avatar
 
🎧 10 years
shorted PS rectifier diode is obvious cap killer... or something else.

JR
Old 2 weeks ago
  #5
alrighty, so a semi-conductor problem not a capacitance problem. How would I go about testing the existing bridging rectifiers? I found a schematic, did a little bit of connect the dots, since it was C14 that was blowing, I traced that back to BR1 (25A-400V).
What would cause the Bridging rectifier to fail?
Attached Thumbnails
Active Speaker Amplifier Capacitance issue-qsc_hpr152i.pdf_2.jpg   Active Speaker Amplifier Capacitance issue-chasis-mounted-rectifier.jpg   Active Speaker Amplifier Capacitance issue-rectifier.jpg  
Old 2 weeks ago
  #6
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JohnRoberts's Avatar
 
🎧 10 years
Heat causes diodes to fail (the silicon melts). The heat comes from power dissipation so a shorted cap could also melt a diode... (they can kill each other).

A VOM can confirm if a diode is shorted. Low impedance caps are not as easy to measure.

JR
Old 1 week ago
  #7
Gear Guru
 
Thomas W. Bethe's Avatar
 
1 Review written
🎧 15 years
Schematic is too blurry to read. Lots of things could cause what you are reporting. I would start with the rectifier and work back from there. FWIW
How good are your electronic chops? What access do you have to test equipment? Lots of unknowns.
Old 1 week ago
  #8
Gear Addict
 
🎧 5 years
Short circuits are difficult to troubleshoot unless you start lifting (unsoldering) suspected shorted parts. If you are not experienced in soldering PCBs you should hand it off to a pro.

(Or start watching everything you can find about it on Youtube and decide which videos are BS πŸ˜†)
Old 1 week ago
  #9
I can solder and De-solder. I have a nice Weller solder station. I have a multimeter, variable voltage regulator, and oscilloscope. The oscilloscope im still learning to navigate. And im still trying to get the hang of reading schematic. I also have been trying to trace out voltage within the circuit using multimeter. Ive got an Electronics Theory book. Which i am flipping through.
As for taking things into a shop... i just dont have the money to pay labor. And this particular speaker I got for a whole $5 + the $16 worth of capacitors
Old 1 week ago
  #10
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Rick Dalton's Avatar
There are four of the caps. C13, C14, C15, C16
Maybe this will help.
Attached Files
File Type: pdf qsc_hpr152i.pdf (680.7 KB, 3 views)
Old 1 week ago | Show parent
  #11
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Rick Dalton's Avatar
Quote:
Originally Posted by coreyspencer ➑️
I can solder and De-solder. I have a nice Weller solder station. I have a multimeter, variable voltage regulator, and oscilloscope. The oscilloscope im still learning to navigate. And im still trying to get the hang of reading schematic. I also have been trying to trace out voltage within the circuit using multimeter. Ive got an Electronics Theory book. Which i am flipping through.
Notice in the schematics Bridge rectifier BR1, has +110 and -110 going to all four of those caps, a component in the the voltage divider circuit has crapped, allowing to full 110v potential. So it's a wonder youre getting by using the 90-what ever volts with out blowing.
Old 1 week ago
  #12
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Rick Dalton's Avatar
And just for a heads-up, over powering those Cap's, that can pretty much, turn them into a 3 inch magnum (Shot Gun Shell without the lead) So don't be overpowering...., and diffidently not with your face over it. If you need to test using that variac, use a probe on that BR1 secondary's and dont let them get over/more than 55 volts.Then remember where the variac voltage is set.
Old 1 week ago | Show parent
  #13
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Rick Dalton's Avatar
Quote:
Originally Posted by coreyspencer ➑️
Repair shop is out of the question..... my question now is what does the (+)( -) voltages written on the PCB signify? i noticed that theres 2 wires coming off transformer, red and blue the red is +110v and is connected directly to the power switch. the blue -110v and was not connected but capped. Why is there an option to use one or the other?

I also considered the shorting, so i just de-gunked the PCB. There was electrolytic juice leftover from the capicitor popping its top.
And as for shorting what other components would allow the whole unit to work just fine between about 58vac and 96vac. But then above that range cause the capicitor to blow.
That blue (capped wire) is on they primary side of the tranny and is most likely used for European power.
Old 1 week ago
  #14
Thanks for the detailed schematic and the pinpoint of problem area and for the safety heads up. As for blown caps, i did experience the shock and awe of a big cap pop, luckily i was not juiced like the inside of the amplifier cavity. Yes, i did find out the blue primary is for 230v.

When using multimeter to trace live circuit. Im still curious about where to place the probes without making any other shorts. But still find out what i need to find out.
Old 1 week ago
  #15
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Rick Dalton's Avatar
Quote:
Originally Posted by coreyspencer ➑️
I don't know or cant figure out why this QSC HPR152i active loud speaker is doing what its doing. So when I opened it up I had noticed that a 63v 6800uf capacitor had puked its guts all over. Figured it was just a matter of replacing the component. So i did that. but then I got a smokeshow. After that i tried a fresh cap. this time i used a variable voltage regulator. The speaker does work fine with the voltage regulator but it will just start smoking when ever it sees anything above 96vac. I was just wondering what the problem is and if there was a way to somehow lower the voltage internally, perhaps a resistor off of the +110v wire coming from the transformer? Or just get a bigger capacitor? Or is there a whole different issue going on?
Which cap blew? C13, C14, C15, C16
Old 1 week ago
  #16
Old 1 week ago | Show parent
  #17
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Rick Dalton's Avatar
Quote:
Originally Posted by coreyspencer ➑️
It was C14
Were those BR1 and BR2 mounted to the chassis? Both of those need checked. You see those wire going to the lugs on that PCB the +110 -110 +55 -55 and GND. Set you DMM to DC voltage and put the negative probe on GND and check with your positive probe, that those voltages are equal off each positive and negative lug of that BR. (you wont get the voltage thats shown o the schematics, because you be using the Variac.
You want to bring your Variac, up slowly and set a limit (dont go over the voltage you were using to make it work before) Also if those BR's were mounted, they really need to be remounted and heatsink compound should be used (you can do that later) But if these BR's are reaching a thermal thresh hold (heat), this could make a diode in them breakdown. Also the Variac is not isolated from the mains, so be careful not touch anything else with ground potential, while poking around in there. Thats just a common warning, but you should be fine. Put shoes on.
Old 1 week ago
  #18
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Rick Dalton's Avatar
Those replacement cap's you got...., do you know anything about them? As in N.O.S or shelf life. They could be just as old as the ones in the amp.
Old 1 week ago
  #19
Dont know much about them other than they're rated for same voltage, same uf(M) and same temp. The one without the wrap is oem.
Attached Thumbnails
Active Speaker Amplifier Capacitance issue-1631675894379656207429706935257.jpg  
Old 1 week ago | Show parent
  #20
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Rick Dalton's Avatar
Quote:
Originally Posted by coreyspencer ➑️
Dont know much about them other than they're rated for same voltage, same uf(M) and same temp. The one without the wrap is oem.
It would be nice if you have some that were higher voltage rating, that you could use for trouble shooting. But those, you'd have to run leads to, (as they'd be way larger, plus they would cost a lot.
Old 1 week ago
  #21
Alright. So i checked the BRs. In circuit. Unpowered. They read like theyre working. I used DMM set on continuity. Went neg probe on pos leg, checked the AC outputs, then switched pos probe on neg leg of BR.
BR1 reads out 492 and 476. BR2 reads out 455 and 480.

About using a higher Voltage capacitor. I was thinking of just throwing a 100v one in there and running with it. The amp does work without C14 in place. Theres just alot of extra noise.

Or what would be the next step in tracing out the problem?
Attached Thumbnails
Active Speaker Amplifier Capacitance issue-20210915_091606.jpg   Active Speaker Amplifier Capacitance issue-20210915_091423.jpg   Active Speaker Amplifier Capacitance issue-20210915_091840.jpg   Active Speaker Amplifier Capacitance issue-20210915_091827.jpg  
Old 1 week ago | Show parent
  #22
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Rick Dalton's Avatar
Quote:
Originally Posted by coreyspencer ➑️
Alright. So i checked the BRs. In circuit. Unpowered. They read like theyre working. I used DMM set on continuity. Went neg probe on pos leg, checked the AC outputs, then switched pos probe on neg leg of BR.
BR1 reads out 492 and 476. BR2 reads out 455 and 480.

About using a higher Voltage capacitor. I was thinking of just throwing a 100v one in there and running with it. The amp does work without C14 in place. Theres just alot of extra noise.

Or what would be the next step in tracing out the problem?
Testing like that isn't going to be accurate. For one you need to check both anode and cathode for leakage and openes. The meter doesn't have diode test setting, does it? Testing in circuit can be reading caps. You need to remove the BR's or make a cut in the traces (then when done spice /solder those traces back. Same with other diodes, you need to lift one leg and test for any leakage. Look up how to test diodes.
Old 1 week ago
  #23
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Rick Dalton's Avatar
How many good caps do you have? If you have an extra two , you can wire them in series and that would double your voltage rating, but cut your capacitance in half, but if you do that with the problem cap C14..., that may keep you up and running to do trouble shooting, with out blowing.
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