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View Full Version : ARC SUB 8 fails the sound is too low



csijo
01-19-2005, 05:41 AM
I live in Venezuela and in my state JBL dont have distributors o service.

I have an "ARC SUB 8" Subwoofer as part of my HT but after a time without use this start to sound too low i opened and i found a resitor and a capacitor die that are place in the area of the conectors of the cables to the speakers.

I need help to Know the numbers of these parts or if posible find the diagram of the motherboard subwoofer for send to a technical service because they say that they need the number of the parts or the diagram to try repair it.

Please help me i will regards so much

Thanks

Jose Ortega
is the first sub from high

file:///G:/Imagenes/Audio/Sistemas/Jose%20Ortega/DSC00507.JPG

file:///G:/Imagenes/Audio/Sistemas/Jose%20Ortega/DSC00509.JPG

Chas
01-19-2005, 06:49 AM
Hi Jose, your sub sounds like a small JBL one I just repaired for a colleague at work. It don't recall the model number, but the driver was quite small, either 6 or 8 inches in diameter.

I had to replace the capacitor only, the original one was a cheap nonpolarised electrolytic that had actually blown to bits before it died. The only thing left were its terminals still soldered to the board and the two pieces of foil (the internal capacitor plates) attached to them. The plates had shorted out the amp output taking the fuse out. I was surprised to actually see a fuse! Even with a fuse, my experience has been that solid state electronics usually protect the fuse!

It appeared that the resistor and capacitor were an RC network across the amp output terminals to provide some HF loading and possibly to snub some HF noise, I suspected that the encapusalted power amp module was some form of swiching amp, class D thingie.

Anyway, the value of the capacitor was about 20 microfarads at 20 volts, if I can recall correctly. I didn't have one available at that point and I ended up using a Solen 14 ufd/400V I had around the shop and replaced the fuse with another 1/2 amp one, except I used a slow blow type. It worked fine after that.

The cap and resistor values used are not that critical, are you sure the resistor is gone? Mine was fine. Can you read the value or the colored bands on it?

csijo
01-19-2005, 06:51 PM
Hi Chas
My situation is exactly to the happened to your colleague at work, the capacitor was in the same way that you describe, the only diference is that the resistor is gone, it converted in dust and is imposible read the colored bands on it.

I replace the capacitor for a new one nonpolarised electrolytic 10 microfarads 100Volt because in the shop i dont find the original value that was: 10 microfarads at 50 volts, but after that change still the problem.

The fuse looks fine, i dont have tools to test but maybe is a good idea changing for the type you suggest, but what values i should use for the resistor?

Maybe the problem is because the resistor is openened, The only things left were its terminals still soldered to the board.

What i should do?
Thanks
Jose

csijo
01-19-2005, 06:54 PM
[QUOTE=Chas]Hi Jose, your sub sounds like a small JBL one I just repaired for a colleague at work. It don't recall the model number, but the driver was quite small, either 6 or 8 inches in diameter.

I had to replace the capacitor only, the original one was a cheap nonpolarised electrolytic that had actually blown to bits before it died. The only thing left were its terminals still soldered to the board and the two pieces of foil (the internal capacitor plates) attached to them. The plates had shorted out the amp output taking the fuse out. I was surprised to actually see a fuse! Even with a fuse, my experience has been that solid state electronics usually protect the fuse!

It appeared that the resistor and capacitor were an RC network across the amp output terminals to provide some HF loading and possibly to snub some HF noise, I suspected that the encapusalted power amp module was some form of swiching amp, class D thingie.

Anyway, the value of the capacitor was about 20 microfarads at 20 volts, if I can recall correctly. I didn't have one available at that point and I ended up using a Solen 14 ufd/400V I had around the shop and replaced the fuse with another 1/2 amp one, except I used a slow blow type. It worked fine after that.

The cap and resistor values used are not that critical, are you sure the resistor is gone? Mine was fine. Can you read the value or the colored bands on it?


Hi Chas
My situation is exactly to the happened to your colleague at work, the capacitor was in the same way that you describe, the only diference is that the resistor is gone, it converted in dust and is imposible read the colored bands on it.

I replace the capacitor for a new one nonpolarised electrolytic 10 microfarads 100Volt because in the shop i dont find the original value that was: 10 microfarads at 50 volts, but after that change still the problem.

The fuse looks fine, i dont have tools to test but maybe is a good idea changing for the type you suggest, but what values i should use for the resistor?

Maybe the problem is because the resistor is openened, The only things left were its terminals still soldered to the board.

What i should do?
Thanks
Jose

Zilch
01-19-2005, 08:30 PM
Hello, Jose. Two suggestions:

1) Contact Harman JBL in your country and tell them your problem. You need the schematic to repair your Arc Sub 8. At least you want the phone number or eMail address of a technician that can help you.

2) Wait a for a forum regular who has access to factory service information to respond. There may also be a technical bulletin relating to that product and particular problem available. Several forum members have access to this, apparently.

Chas
01-20-2005, 05:55 AM
Jose, I am sorry I don't recall the value of the resistor. I think it was a fairly low value in the low tens of ohms and was a 1 or 2 watt value. The thing is, that I don't believe the R/C network as a whole is critical to the overall gain and operation. I hate to say it, but there may be some other damage that hapened, resulting in very low output when the cap and resistor died.