Car Amp in Need of Repair

[Greg Davirro]

Hi,
I have a NVX JAD900.5 car amp that I'm using in a 2.1 configuration in my Chevy truck. Left/Right Front and Single Subwoofer.
For no apparent reason, the LR channels turn off while the subwoofer channel stays on. It has nothing to do with overheating (I don't think) because it will be off when I start the truck after it has been sitting for hours and then after several minutes the LR will come back on...and then off again, seemingly randomly. The subwoofer never shuts off. I believe that if it were an overheating issue, the entire amp would shut down, not just the L/R channels. I have used this amp with a different head unit with the same results, so it isn't the source.
I have 2 options. Take the cover off and try to figure out what part(s) is/are failing or throw it in the landfill and buy a new amp. I'd like to try option 1 first. I'm pretty capable of doing repairs but need some guidance as to what to look for. I don't want to spend a lot of $ on this amp even though when it works, it sounds excellent. Any ideas?
Thanks in advance.

 

[Ylli]

Can't find a service manual/schematic online. If the failure is random, it might be a broken solder joint - a good physical exam would be a starting place. Might be lots of other things too. Hard without a schematic.

 

[Martaine2005]

As mentioned above, an intermittent or random cutting in or out would suggest a bad connection somewhere.
A common car audio problem is third party wiring into front door panels. The door speaker wiring is often a lighter gauge or not routed correctly. This causes stress and breakage of the copper strands between the door and vehicle body.
Has the amp got any indicators (led’s) for L/R or sub?. If yes, do these indicators go out when the L/R channels drop out?.
I would initially try Two important processes of elimination.
1. Open the door/s and play music while rolling the wiring between your fingers or jiggle it around. This SHOULD drop in/out signal to the door speaker suggesting a broken / failing wire.
2. As you have already tried a different head unit, disconnect the front speakers from the amp and connect directly to the head unit. This would then eliminate the amp or prove it to be the source of the problem. Without checking these, there is no way of knowing where to start.

Martin

 

[Greg Davirro]

Thanks for the replies.

I should have been more clear about using a different head unit. The amp was used in a different vehicle in a entirely different system. It was originally used in my Ford Fusion when it started this behavior. I replaced it. I then used it in the system I built for my truck. The reason I was willing to use it in my truck is because I thought the problem was that it was overheating and would shut down when it did. I don't drive my truck very often, or very far when I do, so I thought it wouldn't (or rarely) get hot enough to have this happen. The new amp in my car has never shut down. This is the reason that I know that it isn't the speakers or connection.

 

[Martaine2005]

Ahh, that makes it a lot clearer.
Then yes, crack it open. You’ll need to be able to see both sides of the board. Be careful though, there are likely to be banks of capacitors for each channel that can hold a large voltage.
Check very closely for cracked solder joints, loose components and mechanical connectors.
If there are mechanical connectors, disconnect them and check for corrosion. Sometimes re-seating a couple times cleans the connections.
Take some very clear images of both sides of the board and upload here. I am sure somebody will be able to help.
In the mean time, I will see if there is any info on that amp as I have not done so yet.
You’ll probably need a magnifying glass to check the solder joints. Hair line cracks can be nearly impossible to see. So be thorough and patient.

Martin

 

[Martaine2005]

If you get a drumstick or wooden chopstick, you could put pressure on the relays and the toroids to start with while the unit is powered. Press down on the sister boards and gently put side pressure on the larger components. This MIGHT point out where dry/cracked joints are. Typically in the larger components due to weight and vibration or not secured properly.

Martin

 

[Greg Davirro]

I see you got the photo from Sonic. Good find.
I cracked it open and it didn't take long to find the likely culprit. One of the large capacitors is fried. So bad that I can't read what's printed on it in order to get the correct replacement. Fortunately there's another one next to it that appears to be exactly the same. Hopefully replacing the fried cap will solve the problem. I wonder if the other identical cap is for the subwoofer channel and that is why I never lose that channel. If that's the case, is the other cap possibly a different value? Another question, why would it work intermittently if the cap is that fried.

I must have been cranking the amp pretty hard. Sheeesh!


Thanks again for your replies.

 

[Martaine2005]

The photo was courtesy of Google images!. Tinternet is a wonderful thing.
Yes they are identical and probably in series. I would replace both as the ‘good one’ is probably ‘stressed’. Take note of polarity.
Signal droppping in and out as you describe should still be checked for solder joints while replacing caps.

Martin

 

[WHONOES]

The obvious question is "What caused the capacitor to blow" and would it go again. You probably need to investigate further or monitor the unit for some time after replacing the failed parts.