G’morning all/Perry 🙂
This is my 2nd JL Audio amp repair, came in pretty beat up, looked to be something spilled/ dried in the corner near PS FETs that’s directly across from Pos/Neg/Rem terminals. It starts booting up at about .5a then drops to .001 and low voltage light/blue led kicks on. I’ve let it sit like this for over 30 secs to see if soft start was delayed (per a post I read where it took over 16 secs to boot) and still barely any current draw and low voltage light on.
No FETs test bad, Q512 & Q517 did, replaced with new PN2907A, 2 caps looks slightly bulged and top covers were loose, pulled and tested all caps and all are actually a few hundred over spec, no leaks 🙂 there was pretty bad corrosion on the underneath of the daughter board above the main power terminals as well, one small cap leads actually connected, cleaned it all up and covered area with Kaylon tape to prevent any more, cleaned up all switched and potentiometers very well too, no other parts that I can find test bad, those replacements had no effect on the Low Voltage symptom.
Kind of at a loss of where to start, worried about keeping board powered up in low voltage state out of heat sink (don’t have a thermal imaging cam yet to see if anything is overheating) but didn’t feel any real heat from what I did touch 😅
Any direction would be great, searching forums didn’t help but going to keep on searching via anything on JL in the meantime.
This is my 2nd JL Audio amp repair, came in pretty beat up, looked to be something spilled/ dried in the corner near PS FETs that’s directly across from Pos/Neg/Rem terminals. It starts booting up at about .5a then drops to .001 and low voltage light/blue led kicks on. I’ve let it sit like this for over 30 secs to see if soft start was delayed (per a post I read where it took over 16 secs to boot) and still barely any current draw and low voltage light on.
No FETs test bad, Q512 & Q517 did, replaced with new PN2907A, 2 caps looks slightly bulged and top covers were loose, pulled and tested all caps and all are actually a few hundred over spec, no leaks 🙂 there was pretty bad corrosion on the underneath of the daughter board above the main power terminals as well, one small cap leads actually connected, cleaned it all up and covered area with Kaylon tape to prevent any more, cleaned up all switched and potentiometers very well too, no other parts that I can find test bad, those replacements had no effect on the Low Voltage symptom.
Kind of at a loss of where to start, worried about keeping board powered up in low voltage state out of heat sink (don’t have a thermal imaging cam yet to see if anything is overheating) but didn’t feel any real heat from what I did touch 😅
Any direction would be great, searching forums didn’t help but going to keep on searching via anything on JL in the meantime.
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These amp won't power up with a current-limited power supply. Are you using a 20-30 amp supply with no limiter inline?
O wow I did not know that, no I have been trying to power it up with a 10amp lab power supply. I will try powering it up on my 38AH lithium battery. Although I’m assuming the owner tried powering it up on his vehicles 12v system and was getting the same fault. I’ll find out for certain.
My bad about the slow reply, been so busy with rebuilding subwoofers lately, ‘tis the time for the youngens to blow them ...lol 😅
My bad about the slow reply, been so busy with rebuilding subwoofers lately, ‘tis the time for the youngens to blow them ...lol 😅
Still “Low Voltage” when trying to power it with my lithium battery. What’s usually the first step when diagnosing a “low voltage” problem?
Would Q512 and Q517 being bad have anything to do with it or just an additional find during initial no-power probing?
Im going to see what else I can find online but I don’t think I’ve come across a “Low Voltage” only problem, usually it’s with “Low Ω” light as well.
Would Q512 and Q517 being bad have anything to do with it or just an additional find during initial no-power probing?
Im going to see what else I can find online but I don’t think I’ve come across a “Low Voltage” only problem, usually it’s with “Low Ω” light as well.
Did you repair the damaged vias where there was corrosion?
Does it show low-voltage before the rail supply starts to produce drive pulses?
Does it show low-voltage before the rail supply starts to produce drive pulses?
Yes, corrosion on daughter board 100% repaired.
I haven’t actually put a probe on the amp yet, Low Voltage kicks on right away, current pull starts at .5a then drops to a few milliamperes right away. From my understanding amps do not produce drive waves (same as drive pulses?) until rail supply is at intended voltage. I may be thinking is something totally different then what you are asking, I apologize if I am. I’m not very good with JL amps.
Next move is to order and replace those MMBT3904L BJTs @ Q514 & Q517.
I’ll report back once I do, unless there’s anything else you think I should try next. I’ve just never dealt with a low voltage problem before 😅
Happy Father’s Day to all btw 🙂
I haven’t actually put a probe on the amp yet, Low Voltage kicks on right away, current pull starts at .5a then drops to a few milliamperes right away. From my understanding amps do not produce drive waves (same as drive pulses?) until rail supply is at intended voltage. I may be thinking is something totally different then what you are asking, I apologize if I am. I’m not very good with JL amps.
Next move is to order and replace those MMBT3904L BJTs @ Q514 & Q517.
I’ll report back once I do, unless there’s anything else you think I should try next. I’ve just never dealt with a low voltage problem before 😅
Happy Father’s Day to all btw 🙂
Replaced the Q514 & Q517 with MMBT3904L and still “Low voltage” LED, no others.
As far as Drive pulses on rail supply it does not, it kicks straight into “Low Voltage”
First time troubleshooting something like this, these JL amps have a learning curve and a half 😅
As far as Drive pulses on rail supply it does not, it kicks straight into “Low Voltage”
First time troubleshooting something like this, these JL amps have a learning curve and a half 😅
Post the DC voltage on all terminals of the LM324 near the area where you had the corrosion. Copy and paste the following list and fill in the blanks.
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 1: -5.1mv
Pin 2: +7.36v
Pin 3: +1.25v
Pin 4: +13.5v VCC
Pin 5: +1.27v
Pin 6: +10.22v
Pin 7: -5.0mv
Pin 8: +0.8mv
Pin 9: 11.42v
Pin 10: +1.20v
Pin 11: +0.1v GND
Pin 12: +7.36v
Pin 13: +2.17v
Pin 14: +13.0v
I have removed all transistors along top edge of board, I tried removing output FETs first just to see if there was a problem and anything changed, it changed nothing, same with Power Supply, then Rectifiers, still Low Voltage and all FETs and Rect test good.
If transistors need to be in board for these readings I can reinstall and retake voltage readings on LM324. Board does not have an input signal either.
Pin 2: +7.36v
Pin 3: +1.25v
Pin 4: +13.5v VCC
Pin 5: +1.27v
Pin 6: +10.22v
Pin 7: -5.0mv
Pin 8: +0.8mv
Pin 9: 11.42v
Pin 10: +1.20v
Pin 11: +0.1v GND
Pin 12: +7.36v
Pin 13: +2.17v
Pin 14: +13.0v
I have removed all transistors along top edge of board, I tried removing output FETs first just to see if there was a problem and anything changed, it changed nothing, same with Power Supply, then Rectifiers, still Low Voltage and all FETs and Rect test good.
If transistors need to be in board for these readings I can reinstall and retake voltage readings on LM324. Board does not have an input signal either.
You mentioned pulling the rectifiers, I'm going to assume you checked them as well? I had a bad rectifier that produce low voltage only. First it had a few shorted PS fets and that caused low voltage and ohm light to alternate. Replaced fets with 3709z and the low voltage remained until the 1606ga was replaced.
I had no issues powering mine up with my 10A limiting bench power supply but it was a v2 iirc so maybe that changed. Perry is a god when it comes to amplifier repair so without a doubt listen to him. I lucked out with my JL repair so just sharing my experience.
I had no issues powering mine up with my 10A limiting bench power supply but it was a v2 iirc so maybe that changed. Perry is a god when it comes to amplifier repair so without a doubt listen to him. I lucked out with my JL repair so just sharing my experience.
519mV across the terminals in picture while PSU is on at 14.4v/10a, yet only .020a current draw, blue LED “low voltage” on
I apologize for the length of time between posts, I had a few higher priority repairs come in. This one is now on my bench until I figure it out, and man this is a doozy. I removed all transistors along the top to start with some kind of baseline of getting the PS drive up, but I can’t even get that 😅 ty in advance, I don’t think I can even come close to figuring out this JL without your help Perry. Tysm in advance 🙏🏻
I apologize for the length of time between posts, I had a few higher priority repairs come in. This one is now on my bench until I figure it out, and man this is a doozy. I removed all transistors along the top to start with some kind of baseline of getting the PS drive up, but I can’t even get that 😅 ty in advance, I don’t think I can even come close to figuring out this JL without your help Perry. Tysm in advance 🙏🏻
That Zener diode has either a 5.6 or a 6.2 on it. That's the rated voltage.
Lift the diode and see if it's leaking. If so, replace it.
Lift the diode and see if it's leaking. If so, replace it.
This is embarrassing but I do not know if this is leaking or not from the LCR readings. The amp I have uses the 5.6 diode, pic included. I actually only have experience with the glass axial leaded type of Zener Diodes, I didn’t even know they came as this type. I’m going online now to research it, if there’s another testing method other then my Cheap-O/T7-H, and to find out what exact Zener diode this is and find an exact replacement.
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Checking with a multimeter across the terminals with the arrows should check just like a diode. Current passes one way but not with the probes reversed.
If the diode isn't leaking, there may be a break in the source of voltage feeding it. There is a resistor feeding it. What is the voltage on both terminals of that resistor?
If the diode isn't leaking, there may be a break in the source of voltage feeding it. There is a resistor feeding it. What is the voltage on both terminals of that resistor?
Thank you, really appreciate the tips on taking readings/measuring.
“5.6” as follows with with DMM in diode mode:
Zero reverse voltage
.728v forward voltage
Looks like R427 “224” (which is within spec) is feeding the Zener Diode 5.6, I am barely reading any voltage on that resistor. About 220mV on each end of the resistor. I’m going to remove my kapton tape and check the area more finely
“5.6” as follows with with DMM in diode mode:
Zero reverse voltage
.728v forward voltage
Looks like R427 “224” (which is within spec) is feeding the Zener Diode 5.6, I am barely reading any voltage on that resistor. About 220mV on each end of the resistor. I’m going to remove my kapton tape and check the area more finely
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I don't think that's the right resistor. Follow the trace on the back of the board that leads away from the via on the top of the Zener.
It's not 'zero' reverse voltage. That would be a direct short.
It's not 'zero' reverse voltage. That would be a direct short.
Ahh ok, ty for clarifying, still learning my terminology/how to express what I’m doing technically 😅
So it looks as if there’s 2 resistors on the trace feeding the top leg of the 5.6 Zener. The left bottom leg is connected to the copper backplate, doesn’t look like right bottom leg is used.
i drew it out to be more clear. 14.4v/10a feeding amp.
Looks as only .668v is getting to the top leg of the 5.6 (still removed as in pic) when 12.2v is feeding that trace. The via must be broken/corroded to the point only .668v is passing through right? Arrows drawn on reverse of daughterboard is pointing to via that feeds the top middle leg of the 5.6. Seems that the top leg should be recieving the 12.2v that’s on that trace from what I can see. I didn’t even think a via could break/corrode but it does make sense when specifically thought about.
So it looks as if there’s 2 resistors on the trace feeding the top leg of the 5.6 Zener. The left bottom leg is connected to the copper backplate, doesn’t look like right bottom leg is used.
i drew it out to be more clear. 14.4v/10a feeding amp.
Looks as only .668v is getting to the top leg of the 5.6 (still removed as in pic) when 12.2v is feeding that trace. The via must be broken/corroded to the point only .668v is passing through right? Arrows drawn on reverse of daughterboard is pointing to via that feeds the top middle leg of the 5.6. Seems that the top leg should be recieving the 12.2v that’s on that trace from what I can see. I didn’t even think a via could break/corrode but it does make sense when specifically thought about.
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That is exactly what has happened I think, continuity mode shows there is no contact between the vias, and I think that voltage is from the resistor below. I have micro drills I use for modeling I am now attempting to reconnect the via.
you called it Perry, a break in the trace 🙂 tysm
you called it Perry, a break in the trace 🙂 tysm