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JL Audio A1800 powersupply repair
JL Audio A1800 powersupply repair
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Old 10th March 2019, 08:19 PM   #1
Crazylogix is offline Crazylogix  United States
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Join Date: Apr 2018
Location: The Ozarks, Missouri
Default JL Audio A1800 powersupply repair

Hey guys, working on a JL Audio A1800 that had a totally blown power supply. Output fets do not show shorted in the board. This amp is very similar to the E1800 and the board references that this is the 800x1 design. Board on this one is a 100048 rev 2. So I have removed all the dead power supply fets, drive resistors, emitter follower transistor pairs and 4 small caps in the power supply, all dead or melted. The fact that the emitter-follower tranistors died and a couple desoldered themselves from the board has me worried about damage back at the UC3525ADW drive chip.



Does anyone have the schematic (gotta ask) or the service manual, there are 7 LED's on the board that I think tell you when certain parts of the amp are operating correctly. I am wondering if the LM319 need to check something from the power supply to bring pin 2 high on the 3525.



With everything out, i get D2 and D5 lighting up (yellow) when hooked up to power and remote is on. But I get no drive out from the 3525.


U700-UC3525ADW feeding the amp 12.5 Volts

1. 0v (connected to ground)

2. 0v

3. 0v

4. 0v

5. 0v

6. 0v

7. 0v

8. 0v

9. 0v

10. 0v (shutdown)

11. 0V

12. 0V (ground)

13. 12.0v (Vc)

14. 0v

15. 12.0v (Vin)

16. 0v


Since there is no voltage on pin 10, I would think I would at least get ref voltage out of pin 16. But pin 2 (inverting input) has no voltage on it, this is connected to pin 12 of the LM319. To test a bit further I jumped from U5 (5v regulator) to pin 2 on the 3525, I then got the 5v ref out on pin 16, but still no drive waves from pins 11 and 14.


Hoping someone has a bit of detail on the protection circuit, otherwise I am going to put in the new .1uf caps, drive transistor and gate resistors to see if that gives the LM319 the feedback it wants.


Thanks in advance!
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Old 11th March 2019, 12:05 AM   #2
Perry Babin is offline Perry Babin  United States
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Location: Louisiana
Do you have another 3525 on hand?
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Old 11th March 2019, 12:11 AM   #3
Crazylogix is offline Crazylogix  United States
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Join Date: Apr 2018
Location: The Ozarks, Missouri
No, got a couple in the mouser shopping cart, will double check I don't have one I could steal from another amp when I get home in about 10 minutes. Thinking I should populate the power supply components minus the fets just in case. I did e-mial JL for the schematic, but it's the weekend.
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Old 11th March 2019, 12:45 AM   #4
Crazylogix is offline Crazylogix  United States
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Join Date: Apr 2018
Location: The Ozarks, Missouri
Checked, I have a RF T1500-1bd with a 3526 in it, but i don't want to rob it, it is the one I am working on now and I just got its parts in, so robbing would be bad. I will have to make an order and get some chips. Any other thoughts?
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Old 15th March 2019, 02:11 AM   #5
Crazylogix is offline Crazylogix  United States
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Join Date: Apr 2018
Location: The Ozarks, Missouri
Got in the 3525 today. Still have not swapped them, am trying to trace the LM319 out. Output 1 (pin 12) is supposed to put voltage to pin 2 of the 3525.
LM319
1. 0V NC
2. 0V NC
3. 0V (ground)
4. 0V

5. 3.7V

6. 0V

7. 10.67V

8. 0V (ground)
9. 2.36V

10. 1.58V

11. 12V
12. 0V

13. 0V NC
14. 0V NC


Tracing pin 4 back is such a pain with tons of via's jump back and forth from the top to the underside of the board. Should i just replace the 3525 and start from there since I jumped voltage to its pin 2 and only got ref voltage out of pin 16 but no drive wave? That is what makes sense to me to do, but I am being cautious due to the fact the JL likes to be a little bit special LOL.
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DMM - HP 1222A scope - Hakko FX888D - 50w Unger iron - Yihua 858D Hot Air - 65A power supply (modded dell server) - 1000w 4 ohm test load - test sub - My Youtube repair videos -> Crazylogix
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Old 15th March 2019, 02:29 AM   #6
Perry Babin is offline Perry Babin  United States
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Join Date: Nov 2003
Location: Louisiana
After digging through some notes on other amps, it appears that pin 2 is directly connected to pin 16.
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Old 15th March 2019, 02:47 AM   #7
Crazylogix is offline Crazylogix  United States
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Join Date: Apr 2018
Location: The Ozarks, Missouri
DOH! Yep just checked 2 is connected to 16. So I replaced the chip and was greeted with a wonderful JL regulated (or is it soft start) wave form (not a regular square wave, due to there being no load to speak of to increase the duty cycle). Will be putting the fets all back in and then testing the output, thanks!
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Last edited by Crazylogix; 15th March 2019 at 02:54 AM.
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Old 15th March 2019, 04:03 AM   #8
Crazylogix is offline Crazylogix  United States
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Join Date: Apr 2018
Location: The Ozarks, Missouri
Welllllll.... that was all very anticlimactic. I was breaking my arm patting myself on the back for working so hard to trouble shoot the protection circuit and trace it all back. When I put the new drive chip in, got drive waves, put in new fets, was super careful checking everything as I powered it up, expecting to have to replace outputs (they checked no shorts in the board) and then maybe fix the output drive. NOPE! Amp powers up, perfect high and low side drive, and plays beautiful music. Fresh thermal grease and its time for an endurance burn in. Fixed...huh. I'll take it!
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DMM - HP 1222A scope - Hakko FX888D - 50w Unger iron - Yihua 858D Hot Air - 65A power supply (modded dell server) - 1000w 4 ohm test load - test sub - My Youtube repair videos -> Crazylogix
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