No audio output jl audio 500/5 troubleshooting

[Pbs64133]

I recently have obtained a 500/5 that powers on without the low ohm light but no audio from the front and rear channels. I have checked the rca cables and they are not the problem. I removed the bottom cover and it appears that the output transistors have been replaced. I was wondering where I should start troubleshooting? I have the ability just lack the knowledge for troubleshooting any help would be appreciated

 

[Perry Babin]

Do you have a scope?

Do you have any repair experience?

Have you read the basic amp repair page (in its entirety)? -- link in sig file below.

 

[Pbs64133]

I have read basic amp repair. I have a little experience with replacing transistors and resistors on a jl e1800 that is in my car and working well. Unfortunately I have not been able to buy a scope yet due to lack of funding.

 

[Perry Babin]

Do the op-amps on the preamp board have positive and negative voltage on their power supply terminals?

Does the sub channel work?

 

[Pbs64133]

The sub channel does work and I believe have pos and neg voltage on their power supply terminals. I have not successfully located the pin layout for the op-amps. Would you know the layout so I can be assured I'm checking the right pins?

 

[Perry Babin]

https://datasheet.octopart.com/NJM2068D-NJR-datasheet-96546.pdf

Have you tried connecting signal and speakers and operating all controls (pots and switches on front of the amp) through their entire range to see if any of the dead channels played through (even intermittently)?

Lift (carefully) the preamp board on the connector side about 1/16" (see attached) and push it back down several times to see if that changes anything.

 

[Pbs64133]

I checked the op-amps again and there is pos and neg voltage.

 

[Pbs64133]

I did try every channel while operating the pots and switches while it was in the vehicle. I will try again to make sure.

 

[Pbs64133]

Not sure if its relavant and but only the top two LEDs light up on the audio drivers. I will check the channels while operating the pots and switches as soon as I get home.

 

[Perry Babin]

Is this for all 4 driver boards?

Did all channels go out at once?

The large resistors on the driver boards develop bad solder connections and sometimes have broken terminals. If it's just bad connections, you must add new solder, de-solder and re-solder. If you simply add new solder without removing the old solder, the connections typically fail again.

 

[Pbs64133]

Yes, all four driver boards have only the top two LEDs illuminated. As for the channels going out at once I could not say definitively if they went at the same time. When I obtained the amp I did not check to make sure it had audio I just made sure it powered on. Once I installed it in my vehicle is when I discovered the lack of audio output on the front and rear channels.

 

[Pbs64133]

I have checked the front and rear channels after moving the pre-amp board up and down as you instructed and I have a signal coming from the front left channel as well as the rear left channel but no signal on the front and rear right channel. I will get a new de-soldering braid tomorrow to re-solder the resistors.

 

[Pbs64133]

Would this attachment be relevant to the lack of audio?

 

[Pbs64133]

To make sure I'm checking the op-amps correctly. Do I check the reading between pins 1 & 7 or 2 & 3 as well as 5 & 6?

 

[Perry Babin]

I can't really tell much from that photo. Do you have a better camera?

If you're checking for power on the op-amps, you check on the power supply pins. Not everything on that board is an op-amp.

Are you using 4ch input to check the amp? It tells you more than using 2 channels to feed all 4.

 

[Pbs64133]

I have the input mode on 4ch. I will get a better camera and update the pics. I just powered on the amplifier and went operated the switches and gain. On the front and rear channels I got audio when I was rotating the gain intermittently. The sub channel works

 

[Pbs64133]

Would this resistor be associated with the front and rear channels?

 

[Perry Babin]

That's one of the low-voltage supplies. It could be part of the problem. There is likely some fault that caused it to burn (from what I see). It could have been something like a strand of wire floating around or something else that has failed.

What is the voltage across it?

 

[Pbs64133]

I had a fluctuating reading of -48.4v to -48.9v on one side of the resitor and -1.6 to 1.7v on the opposite side.The driver board U112 led light that is near the two blue capacitors was cycling on and off in sync with the voltage fluctuation.

 

[Perry Babin]

The resistor will need to be replaced. Order replacements if you don't have any. Order extras since the replacement may fail if the fault that caused it may still exist.

Measure the DC voltage on the rest of the 4.,7 ohm resistors in that like of resistors. It should be about the same on both ends of the resistor so you only need to post one voltage for each one.