Help with Orion amp repair

[allorion]

Hello all, I'm hoping someone can help me out with an Orion Cobalt 2100 amplifier. The amplifier is bridgesd to a single 4 ohm sub-woofer. Recently, a stray strand from the remote wire shorted to a speaker wire at the molex connecter.

The result was two fold, an instantly blown fuse in the system fuse block, and I have since found out that the Alpine's remote lead is keeping the amps on with the ignition off as well as keeping its internal amplifier on. I found a blown zener diode in the Alpine CDA-9855 and have ordered another [I hope it's that simple]. I pulled the amp, opened it up and bench tested it. It blew fuses until I limited the current. I noticed one of the power supply FETs was getting very warm and immediatly pulled the power. I don't see any burned traces, burned compononts, or other signs of failure.

I have some experience repairing basic problems with electronic equipment including component replacement, but need a little help to fix it right. My biggest question is what else should I consider replacing? I know I should replace all of the FETs in the power supply and have found suitable compononets thanks to another thread on this site.

Does anyone know of a troubleshooting guide for car audio amplifiers?

Any help, tips, suggestions, etc. would be greatly appreciated.

Thanks - Alan

 

[mike49504]

You need to test all the outputs as well make sure they are fine . nothing should read near 0 ohms.

If you have one that your not sure about post your results.

As far as the guide to amp repair look for Perry Babin's name in a few post on here and click on the links that say basic amp repair ect that will explain alot.

 

[Perry Babin]

After reading the basic amp repair page...
You need to post the DC voltage on all 16 pins of the TL594 (or whatever IC they're using). Copy and paste the following list into your reply. Place the black meter probe on the amplifier's ground terminal. Place the red meter probe on the point where you need to measure the voltage.

IC#
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 15:
Pin 16:

 

[allorion]

Thanks for the quick response, I had time to work on it tonight and this is where I am...

I checked all of the output and supply FETs and found shorts only on one side of the power supply. I pulled them off the board until I was left with one remaining that appeared OK. I powered up the amp with success, no blown fuse [5A], and measured the following voltages

IC# TL494CN
Pin 1: .0093
Pin 2: .0439
Pin 3: .0451
Pin 4: .0128
Pin 5: 1.5633
Pin 6: 3.4707
Pin 7: .0113
Pin 8: 12.294
Pin 9: 5.2654
Pin 10: 5.2884
Pin 11: 12.298
Pin 12: 12.298
Pin 13: 4.9904
Pin 14: 4.9908
Pin 15: .0433
Pin 16: .0113

Supply voltage during testing was 12.312. I couldn't help but notice that I have a hissing sound while powered up coming from something mounted to the board. No signal or speaker was attached. I believe it is coming from one or two FETs from the other side of the power supply. I plan on replacing all 8 in the power supply anyway. The only heat observed came from the coil.

Alan

 

[Kip McGee]

Before you replace those expensive Power supply FETS ,It sounds to me like you need to check for DC voltage coming out of the speaker leads.If you heard a hissing sound something may have the powersupply in a strain causing it to load.Ill bet you a buck you have a damaged amp section probably the output transisters as well as powersupply.
But you can fix it ..Check for DC on speaker leads

 

[allorion]

Could the strain be from running the power supply with one FET on one channel and four on the other? I did not find any voltage on the speaker outputs. Actually my meter read -.25xx VDC across all 4.

 

[Perry Babin]

It appears that the driver IC is driving the FETs.

There are no 'channels' in the power supply. All power supply FETs drive the single transformer that supplies power to both channels. If the single FET on one side of the heatsink is not defective, it should allow the power supply to work properly (at very low power).

Do you read any DC voltage on any of the legs of any of the output transistors? Check all legs of all output transistors.

Place the black meter probe on one of the non-bridging speaker terminals. Place the red meter probe on the point where you need to measure the voltage.

 

[allorion]

Perry- Thanks for the info, I will check them as soon as I get a chance. Alan

 

[allorion]

OK, well, I do have voltage on two legs of the output transistors. When viewing the transistor face up and legs down, the left leg has @28V and the right has 31.25V, 0V on the center leg. This was consistent across all 8 transistors with the voltage varying slightly. Also 1/2 of them showed negative voltage readings.

 

[Perry Babin]

Have you tried connecting a speaker to see if it produces clean audio?

Clamp ALL heatsink mounted components before applying power.

 

[allorion]

I just tested it for audio output. I'm using my computer for source signal and the amp is bridged into an 8 Ohm speaker. It does produce sound. The music is clearly audible and it had no problem making power. I wouldn't exactly call it clean. It has a hiss [similar to white noise] at low volume and no volume with or without source connected I don't recall it being affected by the gain control. It probably wouldn't be an issue in my application, but it does have the potential to run a set of seperates up front sometime down the road. The hiss would drive me nuts in that application. I'm excited to hear it play and grateful for the help getting it to this point. Thanks all. How complicated is it to diagnose the hiss, or should I replace the known defective components at this point and then continue the diagnosis as they may be causing it?

Alan

 

[Perry Babin]

Do you have an oscilloscope?

 

[allorion]

no, but i may have access to one. I will need to see what i can do. Anything I can do without one? Thanks - Alan

 

[Perry Babin]

It would be easier if you had a scope.