The pad for leg 2 is connected to +12 Vdc and a pair of low gauge (heavy) transformer windings.
The pad for leg 3 is connected through a resistor to a pair of high gauge (light) transformer windings, the other ends of which connect to leg 1 of all transistors on a respective side of the power supply.
Legs 2 and 3 are reading 0.6 Ohms, again not at all on the good side. I can't find any devices yet that are reading short or otherwise seem bad. It seems likely there may be a short in the transformer.
The pad for leg 3 is connected through a resistor to a pair of high gauge (light) transformer windings, the other ends of which connect to leg 1 of all transistors on a respective side of the power supply.
Legs 2 and 3 are reading 0.6 Ohms, again not at all on the good side. I can't find any devices yet that are reading short or otherwise seem bad. It seems likely there may be a short in the transformer.
The transformer on the bad side has some crud and kind of light scoring, and is showing some other small signs of damage - it looks worse than the other side's. I guess I have to remove it I don't know what else to try. It's the only thing showing any sign of damage and I can't eliminate it unless I remove it.
Hi Perry,
I only had to disconnect one transformer connection to figure out it probably wasn't the problem.
I traced the problem back to the row of transistors in the picture, disconnecting leads one by one until I saw the impedance move back toward normal.
The fourth transistor down the row is showing very low impedance between pins 1 and 2 even after they are disconnected. It is correct that this indicates a bad device correct?
It looks like it is as you say (of course) and that whole row is bad. The other row in the bad power supply seems like it might be OK.
Now I need to remove them a replace with the correct part, do you know what you'd use for the 5 paralleled on that side, and the one for the drive?
THANK YOU
I only had to disconnect one transformer connection to figure out it probably wasn't the problem.
I traced the problem back to the row of transistors in the picture, disconnecting leads one by one until I saw the impedance move back toward normal.
The fourth transistor down the row is showing very low impedance between pins 1 and 2 even after they are disconnected. It is correct that this indicates a bad device correct?
It looks like it is as you say (of course) and that whole row is bad. The other row in the bad power supply seems like it might be OK.
Now I need to remove them a replace with the correct part, do you know what you'd use for the 5 paralleled on that side, and the one for the drive?
THANK YOU
Now that one side of power supply transistors are completely desoldered, I see that one is showing very low impedance between pins 1 and 2, and the rest don't seem bad. Might as well replace all, I need to figure out how to get them off the clamp they're glued to. They are really on there, I can't get a knife in there to pry them or anything.
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I posted this earlier.
http://www.bcae1.com/temp/orionampclamps.swf
If you're going to replace the transistors, you can just pry them off (don't damage the clamp). For any that you want to try to save, do as suggested above.
http://www.bcae1.com/temp/orionampclamps.swf
If you're going to replace the transistors, you can just pry them off (don't damage the clamp). For any that you want to try to save, do as suggested above.
OK. I just want to remove the few I need to replace without destroying the front (because I need to read the front to try and source them, because I have no idea what to replace them with.) If I try to pry the clamp off, I'm going to tear them all up all will have to do the whole amp, and won't know what to put in because the numbers on the cases won't be readable.
I recemmend that you avoid NTE or any other sub. Use parts purchased from an authorized distributor. Mouser and Digikey are both good choices.
When repairing amps like this, you need to have parts that match closely. You don't have to do any special testing but you should use parts with matching date codes. When ordering small quantities, they sometimes just send what's loose. I'd suggest that you order far more than you need if they won't guarantee matching date codes. That will give you a better chance of having enough matching parts.
Do NOT buy from ebay.
When repairing amps like this, you need to have parts that match closely. You don't have to do any special testing but you should use parts with matching date codes. When ordering small quantities, they sometimes just send what's loose. I'd suggest that you order far more than you need if they won't guarantee matching date codes. That will give you a better chance of having enough matching parts.
Do NOT buy from ebay.
These look like the only available on DigiKey:
2N6488G ON Semiconductor | Discrete Semiconductor Products | DigiKey
They have a nice price break at 50, so I was just going to order and shelve it until they arrive.
2N6488G ON Semiconductor | Discrete Semiconductor Products | DigiKey
They have a nice price break at 50, so I was just going to order and shelve it until they arrive.
I got the transistors today, installed, reassembled amp, and it has been running a while now.
Everything seems normal, sounds very good, probably better.
When I first took the board off the sink, I noticed the clamps were quite loose. Possibly (in addition to being 31 years old) the heat sink mating was to blame.
Perry:
Again, thank you very much for your help - very much appreciated. If you are going to be in the way of the weather heading into the state this weekend, best wishes.
Everything seems normal, sounds very good, probably better.
When I first took the board off the sink, I noticed the clamps were quite loose. Possibly (in addition to being 31 years old) the heat sink mating was to blame.
Perry:
Again, thank you very much for your help - very much appreciated. If you are going to be in the way of the weather heading into the state this weekend, best wishes.
Thank you. I am going to make sure that after some thermal cycling (which will sound pretty good) the board is seated correctly. It didn't quite seat perfectly on the first try because of the rectifiers behind the board.
The clamps were loose when I first tore into it, and when I reassembled it the devices I replaced were the hardest to seat down firmly. Maybe not a coincidence, it is an old amp - who knows.
I probably should have just checked this when I got the amp, and should do so henceforward.
The clamps were loose when I first tore into it, and when I reassembled it the devices I replaced were the hardest to seat down firmly. Maybe not a coincidence, it is an old amp - who knows.
I probably should have just checked this when I got the amp, and should do so henceforward.
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