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.
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.
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.
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
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.
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.
good news and bad news
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.
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.
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.
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?
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.
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.
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.
How big is your test power supply?? I recommend you use at least a 10 amp, and preferably a 15 amp supply.
Many of these older Orions are transistor based power supply and they draw a hugh in-rush current on start up (unlike MosFet power supplies).
And if you don't supply that in-rush current the power supply will fail to start properly and cause excessive current draw, and that funny noise your hearing.
Also, I see all your main power supply caps are BAKED, by that I mean look at the shrink sleeve plastic on the the big blue caps. It has shrunk from Excessive heat build up. Those caps are not long for this world if they are even working properly now at all.
Fresh caps would be nice, as they would significantly improve your turn-on in-rush current, and would clean up the powet supply nicely.
A friend of mine is also reworking one of these Orions as I write this post. I will e-mail his schematic drwaing if you like as its to big for this forum to attach it seems
Good luck and I hope this helps abit🙂 🙂 🙂
Many of these older Orions are transistor based power supply and they draw a hugh in-rush current on start up (unlike MosFet power supplies).
And if you don't supply that in-rush current the power supply will fail to start properly and cause excessive current draw, and that funny noise your hearing.
Also, I see all your main power supply caps are BAKED, by that I mean look at the shrink sleeve plastic on the the big blue caps. It has shrunk from Excessive heat build up. Those caps are not long for this world if they are even working properly now at all.
Fresh caps would be nice, as they would significantly improve your turn-on in-rush current, and would clean up the powet supply nicely.
A friend of mine is also reworking one of these Orions as I write this post. I will e-mail his schematic drwaing if you like as its to big for this forum to attach it seems
Good luck and I hope this helps abit🙂 🙂 🙂
My power supply isn't really a power supply at all.Just a 12 volt sealed lead acid battery that is usually hovering around 13 volts .It has a 17 amp hour rating.I believe it is rated for 400 amps. I've always thought the caps looked strange. Never worried too much about it though.Figured that possibly they looked like that to begin with.
Nah, there pretty shot from the excessive heat they were exposed to. This much heat causes the internal electrolyte to dry up or cook away. and with this things just gets worse from there on out. The visual is the shrunk up sleeves on them. As a rule if the plastic has seen that much heat then the cap was near boiling point thru-out.
You can use a hairdryer to do the heat thing on a test cap to see what I'm saying about how hot these caps have been. Just use a hairdryer on hi heat aimed at a cap for a while you will see the shrinkage of the sleeving, and you can measure the temp required to do this and I think you will be amazed by the temp that those caps have seen.
Anyway, on a amp this old fresh caps are always a good thing to do, if your restoring to like new performance. 🙂
You can use a hairdryer to do the heat thing on a test cap to see what I'm saying about how hot these caps have been. Just use a hairdryer on hi heat aimed at a cap for a while you will see the shrinkage of the sleeving, and you can measure the temp required to do this and I think you will be amazed by the temp that those caps have seen.
Anyway, on a amp this old fresh caps are always a good thing to do, if your restoring to like new performance. 🙂
I wanted you to measure the voltage on the output transistors (using the RCA shiels as the reference) to determine if the power supply was working properly.
If I'm not mistaken, that transistor and resistor supply the bias voltage for the power supply transistors. If justonemoreamp has one on the bench, maybe he can confirm this. If those are getting hot, I would think that there is a defective power supply transistor (especially if they were not running hot before). The resistor will get hot but should not get really hot really quickly.
If I'm not mistaken, that transistor and resistor supply the bias voltage for the power supply transistors. If justonemoreamp has one on the bench, maybe he can confirm this. If those are getting hot, I would think that there is a defective power supply transistor (especially if they were not running hot before). The resistor will get hot but should not get really hot really quickly.
Perry is on something here with his post. I would check this also.
Another way to check for bad power transistor is to simply ohm them out. They are connected in parallel so a short will read across all of them in the set. You can then pull the center lead on each till you have found them one and all that are bad.
Also I would rig your ohm meter in amps range in the 12 volt circuit to actually see what the amps current draw is at on- idle. It should be less than 2 amps for this amp.
My test power supply reads both voltage and current draw on the loads I hook up. This saves alot of time knowing what the real current draw is, as it does signify a whole lot of info about the amp your working on.
As for the amp my friend is restoring curently (a DIY forum member also). He has one open on his bench currently. Thats where I have the partial power supply print from. To my memory it accurate if you think you might need it e-mail and I will send it to you 🙂
THX Perry 🙂
Another way to check for bad power transistor is to simply ohm them out. They are connected in parallel so a short will read across all of them in the set. You can then pull the center lead on each till you have found them one and all that are bad.
Also I would rig your ohm meter in amps range in the 12 volt circuit to actually see what the amps current draw is at on- idle. It should be less than 2 amps for this amp.
My test power supply reads both voltage and current draw on the loads I hook up. This saves alot of time knowing what the real current draw is, as it does signify a whole lot of info about the amp your working on.
As for the amp my friend is restoring curently (a DIY forum member also). He has one open on his bench currently. Thats where I have the partial power supply print from. To my memory it accurate if you think you might need it e-mail and I will send it to you 🙂
THX Perry 🙂
did a little more playing around. While studying the circuit board I found a power supply transistor with one of its legs not quite touching the solder pad.No continuity at all so I resoldered it.I have not found any shorted power supply transistors so I checked the voltage at the output transistors as you told me to perry and I'm getting almost 40 volts dc . Is this a good number or should it be more/less?That one resistor and transistor do not appear to be getting hot anymore.The resistor has a little heat to it but the transisor is fine.It is not shorted either.
well it looks like I'm back to square one now.While I was typing my last message the amp made a high pitched squeal blew my fuse and I think it may have even took my newly replaced 6491s with it along with the rest of the transistors in that output channel.All of the legs are measuring 60 ohms at the most and just 5 ohms on the low end.I fear some of my power supply transistors may have gone with it as it seems like the resistance readings have dropped a bit.At this point I might as well replace every transistor in the amp.The led on the amp may have been burnt out as before the blowout I was reading voltage across it. Maybe I could have gotten a little play time out of it.
can the power on LED be replaced with any LED or am I looking for a specific part?Do you guys think if I replace all the transistors that I might be good to go being that there was voltage present at all the output transisors?I plan on replacing all of the larger caps as well.
When working on an amp that's not mounted to its heatsink, you MUST monitor the temperature of the transistors. When out of the sink, many times the output transistors will go into thermal avalance and fail (sometimes taking the power supply with them). If it was mounted into the sink, you may have had a defective (leaking/shorted) driver transistor that caused the failure.
For output transistors, you often have only one of the group fail (just as you did originally). Remove the ones with the lowest readings to see if it will return to operation.
±40 volts is probably about right for the rail voltage in that amp.
As far as I know, the LED is nothing special (except possibly the shape of it). LEDs have polarity. If you install it backwards, it won't work.
For output transistors, you often have only one of the group fail (just as you did originally). Remove the ones with the lowest readings to see if it will return to operation.
±40 volts is probably about right for the rail voltage in that amp.
As far as I know, the LED is nothing special (except possibly the shape of it). LEDs have polarity. If you install it backwards, it won't work.
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