Old School Orion 2150 gx.I must repair this amp

[spooney]

well wish me luck on this fix.With any luck I can pick up these parts right here in town.If not I'll order elsewhere and hopefully see them within a week.I'm feeling pretty good about fixing this amp after getting my majestic 4 channel up and running again.

[spooney]

I got lucky today and scored the lm337t that i needed here in town.I also found the 2n6491 that I was looking for but they only had three and I need at least 4.Plus they were asking way too much for them.Almost 5 bucks a piece.I'll have to grab some online to get what I need and save some cash.

[Perry Babin]

Order from a good distributor like digikey or mouser. They will have fresh, first quality parts from high quality manufacturers. Don't buy NOS parts to try to save money. NOS can be OK when you have the equipment to check them properly. Since you won't have that equipment, you won't be sure that they're up to spec.

[spooney]

what can I use to replace the "tape" that sits underneath all the transistors?Most of it came off with the individual parts.does it need to be replaced?seems like i've seen some amps with none at all

[Perry Babin]

The insulator must be replaced. I generally use Kapton tape. At mcmaster.com, the part number for the short roll (15ft) is 7648A715. The 36 yard long roll is part number 7648A34

You must remove 100% of the old insulator from the transistors and the heatsink wherever you're going to replace the insulating tape. If you don't, the transistors will run hot (and possibly fail).

You should also replace the foam tape on the bottom side of the clamps. A wire wheel on a bench grinder is the quickest way to remove it. A belt sander also works well but you have to be careful not to cut into the aluminum.

[spooney]

well I replaced all the parts I originally found to be bad.4 2n6491 transistors and one lm337t voltage regulator.Upon applying power to the amp i was happy to see that it did not fry the fuse as it had before.However it also did not actually power up.No power LED for me.I'm thinking the problem lies or at least starts in this region of the circuit board.I measured 1.18 volts at the input of the MCT2 IC on the right and also measured outputs in excess of 12 volts coming out of pins 4,5, and 6. The other MCT2 IC on the left is a different story.I have the same 1.18 volts at input but nothing out of any of the other pins.Could this be whats keeping the amp from coming on?I'm also getting some funny voltage measurements out of the diodes directly above this IC.

[Perry Babin]

What were you using for the ground reference (where was the black meter lead)? You need to use the secondary ground. The shield ground of the RCAs is a good reference. Try reading the voltages again with this reference.

[spooney]

I used the ground right at the battery cable.I'll try as you suggested.What kind of voltage should I be looking for out of these two ICs?

[Perry Babin]

Those two ICs aren't really important at this point.

Have you tried connecting speakers and signal to it to see if it plays?

Measure the DC voltage on the outputs. You should have rail voltage on two pins of each output and 0 volts on the other pin.

Also measure the voltage on pins 4 and 8 of the 8 pin preamp ICs.

[spooney]

by measuring the dc voltage at the outputs do you mean output transistors?Kinda had some new stuff going on with this amp today.I hooked up power to it and it blew the fuse.I tried again and it held up with a new fuse but it was making this strange high frequency noise when I applied power.One of the transistors directly above the smaller coil that is directly to the right of the huge caps in the center of the amp got hot very fast as did a large gray resistor in that general area.