Orion HCCA 275G4

[Itsme]

This amp is kicking my butt. When I got the amp I replaced a bank of NDP7060's only 4 of them were bad but I replaced all 6. Also replaced the TL494CN, It looked like it had been hot along with 2- 47uf 25volt and 1- 1uf 50volt caps next to the TL494CN. I then installed 1- 5 amp fuse on the left channel and one on the right channel. Powered it up and was getting loud humming on both channels, like when the RCA's aren't grounded. Music wasn't loud either. Then the fuse went. checked all the NDP7060's and found one bad that I installed. Replaced it. Replaced fuse and powered on again. Then 2- 2N5639's OP amp's popped. So I then noticed that when handleing the cicuit board I had smashed some other op amps over and they were shorting on some nearby resistor's in the preamp section. Which is why I was getting the humming noise in the speakers. So I made repairs and replaced the 2- 2N5639's and powered up again. No humming this time but only stayed on for 10 seconds and blew the right channel fuse. This amp has 3 - 30 amp fuse's per channel. 180amps total, So I tried a 10amp on right channel and it stayed on alittle longer but the speaker made like a melting noise before it blew the R. channel fuse again. I don't know where to go from here. PLEASE HELP ME...

[Itsme]

Also in the pic above with the TL494 the multi resistor I accidently removed thinking it was one side of the TL494 and it got pretty hot, Would that hurt it? Also on the bottom of that resistor somebody ran a jumper from one leg to another. I don't think this amp had ever been opened before so maybe it was a design flaw and the factory jumpered it? Here is a picture of the bottom.

[jol50]

What is the voltage on the speaker terminals?

[Itsme]

Here is the whole board top.

[Itsme]

Also it was the left channel that I had to replace the NDP7060's in. The right channel fet's were fine. But for some reason it is the right channel blowing fuses now. Fet's are ok.

[Itsme]

Originally posted by jol50
What is the voltage on the speaker terminals?

With music or no music?

[Perry Babin]

The 2N5639 is a jfet. It's used in the muting circuit.

http://www.onsemi.com/pub/Collateral/2N5638-D.PDF

If one channel is blowing fuses, you need to isolate the problem. If you have a 2 ohm resistor, it will make it easier. Running through the resistor, you can measure the voltage across the emitter resistors in the audio section. If the voltage across any resistor is more than ~0mv, you need to determine why. Compare the voltage across the emitter resistors on the good channel to those on the bad channel.

Be careful. Even though you're using a resistor to limit current, it doesn't mean that it will prevent damage. Have all components clamped to the sink to help insure that nothing will be damaged.

If there is absolutely no voltage across the emitter resistors on either side, the problem is likely in the power supply. If half of the FETs in the defective channel are getting hot, the problem is probably in the drive circuit. Remember that these Orion amps often blow the driver transistors and the 10 ohm collector resistor of the PNP driver transistors.

For the 1% components, the resistor color code for the 10 ohm resistor is brown, black, black, gold, brown. One end of the resistor will go to the third leg of the MPSA56. The other end will go to ground.

[jol50]

Originally posted by Itsme

With music or no music?

With nothing but power hooked to amp, but what Perry said will show even more. Should do that with it unhooked and idle too. Watch out for hot things, if sink gets hot at a chip(s) shut it off and let it cool and start testing again. Or if you smell or feel heat/etc. The resistor helps cut the power supply and fuses might save parts. Man that is a big amp.

Checking the output resistors will tell if you have some kind of feedback/etc that is running current through the outputs that should not be. Nothing hooked up to amp=no music out=0 current in outputs or very close to 0. If no current then like he said you know it is likely a power supply problem.

[Itsme]

I haven't tested yet, just after reading your responses I went and checked my 8 ohm bookshelf speaker I use to test my amps with and now it is a 0.1 ohm speaker.

So apparently I am getting alot of voltage through my speaker outputs.
I will test like you said, But what if it keeps blowing the fuse before I can test? Is there any testing I can do without powering up first? thanks.

[Perry Babin]

You should always have capacitors in series with test speakers. 100uf 100v non-polarized are a good choice.

You can easily check the power supply driver transistors and resistors.

Do you know if the speaker was damaged before you repaired the amp or after you replaced tha parts?

If it's blowing fuses, it's unlikely that it could produce enough voltage to damage the speaker even if there was a problem in the audio section.

If the rectifiers are easy to remove, pulling them from the defective channel will isolate the audio section from the power supply section. If the fuse blows without the rectifiers, you have power supply fault. It coud be defective driver components or possibly a shorted transformer.