Re: Re: Self Appointed Audio Repair God's
I have helped a number of newbie's in the past and if you'd bother to search you'd already know that.
There is no reason that he can't tackle this with some help.
The outputs don't even have to be matched. He could just measure them and vary the load sharing resistors as a cheaper alternative.
You post gets exactly to the attitude that I called Anatech on. How do you know that the guy isn't extremely bright and wouldn't pick this up in no time. You don't, and instead decided to make a judgment before he was given a chance.
Give me a break!
moamps said:
I have helped a number of newbie's in the past and if you'd bother to search you'd already know that.
There is no reason that he can't tackle this with some help.
The outputs don't even have to be matched. He could just measure them and vary the load sharing resistors as a cheaper alternative.
You post gets exactly to the attitude that I called Anatech on. How do you know that the guy isn't extremely bright and wouldn't pick this up in no time. You don't, and instead decided to make a judgment before he was given a chance.
Give me a break!
Hi Nelson,
He received the amplifier disassembled with an estimate for repair. Some resistors burned.
He may possibly be able to repair it, but more likely not if he can not take advice.
No, you do not have to match the outputs, but the performance is better if you do. He has an opportunity to do this. It is normal service procedure with good tech's to do this.
Remember too Nelson that when you receive transistors from the manufacturer, they are normally in the same lot and will be close in beta. In service quantities they can be easily out by three to one.
-Chris
He received the amplifier disassembled with an estimate for repair. Some resistors burned.
He may possibly be able to repair it, but more likely not if he can not take advice.
No, you do not have to match the outputs, but the performance is better if you do. He has an opportunity to do this. It is normal service procedure with good tech's to do this.
Remember too Nelson that when you receive transistors from the manufacturer, they are normally in the same lot and will be close in beta. In service quantities they can be easily out by three to one.
-Chris
Hi Steve,
Okay. I'll call you on this. I agree to let you contact him off line and let you start a thread for him. I will not post or moderate this thread. In other words, you can attempt this with the help of the entire forum and no interference from me. Milan may agree to this as well.
I will apologize here and now for my reaction to this member.
What do you say?
-Chris
Edit:
Just a thought.
Okay. I'll call you on this. I agree to let you contact him off line and let you start a thread for him. I will not post or moderate this thread. In other words, you can attempt this with the help of the entire forum and no interference from me. Milan may agree to this as well.
I will apologize here and now for my reaction to this member.
What do you say?
-Chris
Edit:
No. Emitter resistors affect current sharing at higher currents. It's the crossover region where beta makes a larger difference. So do not play with emitter resistor values.
Just a thought.
Sounds good.
You guys don't have to disappear from the thread, just give the guy a chance that's all.
I already tried emailing him directly as well. Haven't heard anything back...
[Q]No. Emitter resistors affect current sharing at higher currents. It's the crossover region where beta makes a larger difference. So do not play with emitter resistor values.[/Q]
Ok - just figured he might be able to more easily get close to the good ones he still has in the amp.
Thanks,
You guys don't have to disappear from the thread, just give the guy a chance that's all.
I already tried emailing him directly as well. Haven't heard anything back...
[Q]No. Emitter resistors affect current sharing at higher currents. It's the crossover region where beta makes a larger difference. So do not play with emitter resistor values.[/Q]
Ok - just figured he might be able to more easily get close to the good ones he still has in the amp.
Thanks,
Re: Re: Re: Self Appointed Audio Repair God's
As we all have.
There is a reason: people were bending over backwards to help him and all he had to say was that the thread was a complete waste of time. I'd expect an apology when/if he comes back.
He was given a chance (see above).
I repeat, it is quite unreasonable to try to make a complete newbie repair a piece of equipment running at +/-70V and using 16 output transistors per channel. The best thing that may happen is that he destroys the amplifier beyond help and the worst thing is that he could get seriously hurt in the process.
In another thread, barchetta did not know what a cascode was. Does anyone really expect him to be able to check transistors/parts to see whether they're working or not. Besides, the amplifier looks like it was serviced (butchered up) a few times before and only God knows what awful things may have been done to it. Even if barchetta were the next Tesla, it would still be a challenge to fix that mess.
Regards,
Milan
Apogee said:
As we all have.
There is a reason: people were bending over backwards to help him and all he had to say was that the thread was a complete waste of time. I'd expect an apology when/if he comes back.
He was given a chance (see above).
I repeat, it is quite unreasonable to try to make a complete newbie repair a piece of equipment running at +/-70V and using 16 output transistors per channel. The best thing that may happen is that he destroys the amplifier beyond help and the worst thing is that he could get seriously hurt in the process.
In another thread, barchetta did not know what a cascode was. Does anyone really expect him to be able to check transistors/parts to see whether they're working or not. Besides, the amplifier looks like it was serviced (butchered up) a few times before and only God knows what awful things may have been done to it. Even if barchetta were the next Tesla, it would still be a challenge to fix that mess.
Regards,
Milan
Well; if it weren't for Steve's kind email I would not have come back here.. but when he told me Mr. Pass responded curiosity got the better of me..
Lets just say I will take some of the blame for the misunderstanding and leave it at that... fact is I am thin skinned.
So, someone here; has offered to repair the unit and restore it for a very reasonable price.. but, if I can fix the unit myself and learn in the process I would be thrilled.. Not to mention I own another so this would certainly help me repair that unit if it ever fails. I never dreamed you guys and especially Mr. Pass would be willing to point me in some directions. If this is really true I'd like to take you guys up on your extemely generous offer..
To answer Nelson Pass (and I love how analytical his question was).. we only know this unit is broke because there is a burned resistor at the left output jack. That is the only real answer to the question. There is also data from the previous owner which suggests one side got hot and went bad.. and then the parts list from the repair person.
I posted some hi res pics here:
http://www2.snapfish.com/thumbnailshare/AlbumID=142290232/a=84443094_84443094/t_=84443094
And can post more if it will help.. Not sure where to start.. I was just going to order all caps; and maybe a bunch of power transistors.. drivers, etc.. my approach without assitance was just gonna be to replace everything but the resistors because those are easy to test once I have removed all the other components. And frankly its the only component besides maybe a single diode that I know how to test..
I have been to some general electronic training.. but that was years ago.. and I just know a little theory.. like what resistors do in parallel vs. serial; function of a diode; transistor etc.. thats about it.. I use a multimeter a lot and can measure ohms and volts.. but testing a transistor? No idea... I just know it acts like a switch... sorta.
Anyway; if this is gonna be too much of a hassle let me know.. My original question was really all I was looking for here.. I thought I'd just research the rest..
Anyway.. either way lets move on.
Lets just say I will take some of the blame for the misunderstanding and leave it at that... fact is I am thin skinned.
So, someone here; has offered to repair the unit and restore it for a very reasonable price.. but, if I can fix the unit myself and learn in the process I would be thrilled.. Not to mention I own another so this would certainly help me repair that unit if it ever fails. I never dreamed you guys and especially Mr. Pass would be willing to point me in some directions. If this is really true I'd like to take you guys up on your extemely generous offer..
To answer Nelson Pass (and I love how analytical his question was).. we only know this unit is broke because there is a burned resistor at the left output jack. That is the only real answer to the question. There is also data from the previous owner which suggests one side got hot and went bad.. and then the parts list from the repair person.
I posted some hi res pics here:
http://www2.snapfish.com/thumbnailshare/AlbumID=142290232/a=84443094_84443094/t_=84443094
And can post more if it will help.. Not sure where to start.. I was just going to order all caps; and maybe a bunch of power transistors.. drivers, etc.. my approach without assitance was just gonna be to replace everything but the resistors because those are easy to test once I have removed all the other components. And frankly its the only component besides maybe a single diode that I know how to test..
I have been to some general electronic training.. but that was years ago.. and I just know a little theory.. like what resistors do in parallel vs. serial; function of a diode; transistor etc.. thats about it.. I use a multimeter a lot and can measure ohms and volts.. but testing a transistor? No idea... I just know it acts like a switch... sorta.
Anyway; if this is gonna be too much of a hassle let me know.. My original question was really all I was looking for here.. I thought I'd just research the rest..
Anyway.. either way lets move on.
Look at it this way: A transistor is two diodes, back-to-back. There are more sophisticated ways to go about it, but if you test from the base to the emitter, one way will show infinite resistance (or damned close to it), the other way will show something close to a dead short. Same thing for the base to collector pins. If you get a short both ways, or open both ways, set that transistor aside--it's kaput.
For the time being, you can start by testing the output devices, because it's possible verging on probable that at least one of those is fried. Don't stop just because you find one. Keep going. Test them all. It's a pain in the butt, but it needs to be done.
Can both channels be dead? Yes. Is it likely? No way to tell. Depends on what went wrong when the amp blew. Lightning? Shorted speaker cables? Owner screwup? Who knows? For the time being, concentrate on the channel you know to be dead. Nelson designs his amps such that they can safely run on one channel. You can completely unhook the other channel if you want to.
Another good, quick thing to do is test the voltages at the big power supply caps with the known dead channel unhooked. The terminals bridged by the metal strap are going to be ground. Test from there to each of the other terminals. You should find something like +57V at one terminal and -57V at the other. If you've got that, or something within a couple of volts of that, it's a safe bet that the power transformer, rectifier, and caps are good to go.
(Later on, you might want to swap out the big power supply caps simply because they get cranky as they get older, but if they'll hold juice they'll do for present purposes. Besides, they get expensive.)
Grey
For the time being, you can start by testing the output devices, because it's possible verging on probable that at least one of those is fried. Don't stop just because you find one. Keep going. Test them all. It's a pain in the butt, but it needs to be done.
Can both channels be dead? Yes. Is it likely? No way to tell. Depends on what went wrong when the amp blew. Lightning? Shorted speaker cables? Owner screwup? Who knows? For the time being, concentrate on the channel you know to be dead. Nelson designs his amps such that they can safely run on one channel. You can completely unhook the other channel if you want to.
Another good, quick thing to do is test the voltages at the big power supply caps with the known dead channel unhooked. The terminals bridged by the metal strap are going to be ground. Test from there to each of the other terminals. You should find something like +57V at one terminal and -57V at the other. If you've got that, or something within a couple of volts of that, it's a safe bet that the power transformer, rectifier, and caps are good to go.
(Later on, you might want to swap out the big power supply caps simply because they get cranky as they get older, but if they'll hold juice they'll do for present purposes. Besides, they get expensive.)
Grey
I no longer have the ability to edit my posts so sorry for the additional posts.. I think this link will work now.. I didn't realize that where I was storing my photos did not allow external links.. looks like these guys do.. so try this..
http://joeprinz.dotphoto.com/
http://joeprinz.dotphoto.com/
Hi Joe,
Glad you're back.
I'd agree with Grey that the first place to start is the power supply.
Looking carefully at the pics, it appears that both channels have been disconnected. Is that true, or are my eyes deceiving me?
Also, it appears that on the left channel (when viewed from front) one of the outputs down low is different. Is it a different part number from the others near it and does it also have a different looking match on the other side? Or, has the left channel been worked on also?
A couple of overall pics would be helpful so we can see the whole thing at once.
Also, it goes without saying to watch yourself in there when the power's on. Even after you turn if off, the main caps will hold a charge for a bit so best beware.
This is especially true right now with both channels disconnected. There are no bleed resistors on the main caps so they have lots of juice in them. It might not be a bad idea to add bleed resistors or at the very least a couple on alligator clips to slowly bleed them down while you're working on it.
By the way, it's not a good idea to short them with a screwdriver to discharge them. Yes, you can do it, and yes it will discharge them. But, it's awfully hard on the caps that way. Gentle is always better...
Then again, you did mention that you like smoke tests...
Glad you're back.
I'd agree with Grey that the first place to start is the power supply.
Looking carefully at the pics, it appears that both channels have been disconnected. Is that true, or are my eyes deceiving me?
Also, it appears that on the left channel (when viewed from front) one of the outputs down low is different. Is it a different part number from the others near it and does it also have a different looking match on the other side? Or, has the left channel been worked on also?
A couple of overall pics would be helpful so we can see the whole thing at once.
Also, it goes without saying to watch yourself in there when the power's on. Even after you turn if off, the main caps will hold a charge for a bit so best beware.
This is especially true right now with both channels disconnected. There are no bleed resistors on the main caps so they have lots of juice in them. It might not be a bad idea to add bleed resistors or at the very least a couple on alligator clips to slowly bleed them down while you're working on it.
By the way, it's not a good idea to short them with a screwdriver to discharge them. Yes, you can do it, and yes it will discharge them. But, it's awfully hard on the caps that way. Gentle is always better...
Then again, you did mention that you like smoke tests...
Hi Steve,
Yes, you are correct; all the outputs are diconnected and I will add a few more pics right after this.
In reading over your personal emails... I'd like to respond here so everyone can see..
I agree a starter project would help out with my solder skills; however I actually do have very good soldering skills. In fact I just last week carried out (successfully I might add!) an opamp upgrade on my Onix CD player.. it was a simply dip converter upgrade (2 to 1) but require very precise soldering on small joints. So I am pretty good there.. I know what its like to lift a trace.. it aint pretty.
(Oh and I used to work on monitors where I'd discharge with a screwdriver.. so I am glad you mentioned that about the caps; cuz thats EXACTLY what I was going to do).
Frankly; I do not know which part is the power supply.. I mean I know what a transformer is and I know what a rectifier is (could the the rectifier have gotten hurt? It LOOKS ok).
So not sure where to start.. you mention in your email that
all I will need to test each of the 2n5878's and replace each one thats broke (should I order a bunch from that website I showed you for a $1.80 each just so I have them?).. and should I just go ahead and get a tester at the same time?
Seems like I have lots of ordering to do before I can even start.. like to get a good starter list. All the caps should be done; I might need help understanding what the values equate to part #'s if that makes sense (caps usually dont have part #'s right?)..
Okay.. off to take some more shots of the "beast".
They should be up for viewing; same link shortly...
I will go as hi res as that site will offer me.. pretty cool site by the way.. not many offer external links
-Jpe
Yes, you are correct; all the outputs are diconnected and I will add a few more pics right after this.
In reading over your personal emails... I'd like to respond here so everyone can see..
I agree a starter project would help out with my solder skills; however I actually do have very good soldering skills. In fact I just last week carried out (successfully I might add!) an opamp upgrade on my Onix CD player.. it was a simply dip converter upgrade (2 to 1) but require very precise soldering on small joints. So I am pretty good there.. I know what its like to lift a trace.. it aint pretty.
(Oh and I used to work on monitors where I'd discharge with a screwdriver.. so I am glad you mentioned that about the caps; cuz thats EXACTLY what I was going to do).
Frankly; I do not know which part is the power supply.. I mean I know what a transformer is and I know what a rectifier is (could the the rectifier have gotten hurt? It LOOKS ok).
So not sure where to start.. you mention in your email that
all I will need to test each of the 2n5878's and replace each one thats broke (should I order a bunch from that website I showed you for a $1.80 each just so I have them?).. and should I just go ahead and get a tester at the same time?
Seems like I have lots of ordering to do before I can even start.. like to get a good starter list. All the caps should be done; I might need help understanding what the values equate to part #'s if that makes sense (caps usually dont have part #'s right?)..
Okay.. off to take some more shots of the "beast".
They should be up for viewing; same link shortly...
I will go as hi res as that site will offer me.. pretty cool site by the way.. not many offer external links
-Jpe
Okay I uploaded photos but they only allow one size for viewing.. and you cant read the #'s.. so here they are...
left front
CLASSA6 8039
2N5876 7939
"
"
"
CLASSA6 8113
Left rear
2N5878 7713
8113 SASSIS NPN
2n5878 7713
8113 STASIS
2N5878 7713
"
Right front
ALL - 2N5878 7713
Right Read
ALL - 2N5876 7713
So looks like the left side was repaired.
On another note: I lightly pushed the power lead to the power switch away to read the #''s and it just snapped right off the soldered connection.. I am starting to think this side got extemely hot and all solder joints were compromised... so I know I will need to retouch each connection at a minimum.. hell maybe this unit is okay and just has a cold solder joint or 7.
http://www.dotphoto.com/go.asp?l=joeprinz&AID=4272491
-j
left front
CLASSA6 8039
2N5876 7939
"
"
"
CLASSA6 8113
Left rear
2N5878 7713
8113 SASSIS NPN
2n5878 7713
8113 STASIS
2N5878 7713
"
Right front
ALL - 2N5878 7713
Right Read
ALL - 2N5876 7713
So looks like the left side was repaired.
On another note: I lightly pushed the power lead to the power switch away to read the #''s and it just snapped right off the soldered connection.. I am starting to think this side got extemely hot and all solder joints were compromised... so I know I will need to retouch each connection at a minimum.. hell maybe this unit is okay and just has a cold solder joint or 7
.http://www.dotphoto.com/go.asp?l=joeprinz&AID=4272491
-j
GRollins said:
Just caught this post.. I'll probably follow this advise today and report back.. I'm anxious to know if the filters are good so this will tell me that.. frankly I am not sure which side was dead.. I will see if I can find the ebay auction.. I think he mentioned it in the auction.. it IS obvious to me which side got hot though.. so I am guessing its the right channel... I think thats what he mentioned too..
Oh, one thing.. so I can safely power up the trans/rectifier/filter caps with no load? Just want to be sure... basically thats the way it is now.. all power leads are desoldered by the repair tech.. I think he had the right side board out as well.. many bolts are out...
Morning Joe,
A couple of quick answers for you:
Soldering - skills sound good! Just be wary of old boards...enough said! If that channel has already been worked on multiple times, (and based on the outputs it appears it has) I figure the other techs might have already messed it up a bit. Time will tell... Looking at the variety of outputs in your list, it does look like we have our work cut out for us.
Power supply = xformer, bridge rectifier and caps. Check this thread out:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=92292&perpage=10&highlight=&pagenumber=1
I'd first check the power supply as Grey mentioned. If the voltages read ok, then great. If not, then drain the filter caps and disconnect them. Use your meter to check each one. Charge the cap under test up with the meter leads one way then swap them and watch what happens. You should see a swing to the opposite voltage that slowly drops to zero then starts climbing again. What we don't want to see is a steady reading. Should you see steady resistance, it would indicate a shorted filter cap. (do this test after the caps have been discharged and your bleed resistor has been disconnected)
You can check the rectifier easily also. Search for bridge rectifier and you will find it's just 4 diodes in that block.
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/rectbr.html
If your meter has a diode test setting, just use that. If not, you can test them using the lowest resistance setting. It they're good, you should have continuity one way (I would guess ~.5xx or so) and open the other when you reverse the leads.
If all checks well, I'd hook up the "good" channel, isolate the power leads on the bad channel and let her rip.
Measure for DC at the speaker terminals of the "good" channel with it on. Hopefully you will have none or very little. If all is well so far, then try with an old speaker and a source to see if it makes music - hopefully it will! (remember, only hookup and disconnect sources and loads with it turned off)
At least we would then know if one or both channels need work.
I'd hold off buying parts until you know exactly what you need. For example, if the 2n5876's are shot, they are going to be tough to source. If it were me and that was the case, I would then seriously consider fitting the whole amp with new Motorola MJ series parts and keeping the good 2n parts as spares for your other amp. Food for thought...
Keep us posted.
A couple of quick answers for you:
Soldering - skills sound good! Just be wary of old boards...enough said! If that channel has already been worked on multiple times, (and based on the outputs it appears it has) I figure the other techs might have already messed it up a bit. Time will tell... Looking at the variety of outputs in your list, it does look like we have our work cut out for us.
Power supply = xformer, bridge rectifier and caps. Check this thread out:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=92292&perpage=10&highlight=&pagenumber=1
I'd first check the power supply as Grey mentioned. If the voltages read ok, then great. If not, then drain the filter caps and disconnect them. Use your meter to check each one. Charge the cap under test up with the meter leads one way then swap them and watch what happens. You should see a swing to the opposite voltage that slowly drops to zero then starts climbing again. What we don't want to see is a steady reading. Should you see steady resistance, it would indicate a shorted filter cap. (do this test after the caps have been discharged and your bleed resistor has been disconnected)
You can check the rectifier easily also. Search for bridge rectifier and you will find it's just 4 diodes in that block.
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/rectbr.html
If your meter has a diode test setting, just use that. If not, you can test them using the lowest resistance setting. It they're good, you should have continuity one way (I would guess ~.5xx or so) and open the other when you reverse the leads.
If all checks well, I'd hook up the "good" channel, isolate the power leads on the bad channel and let her rip.
Measure for DC at the speaker terminals of the "good" channel with it on. Hopefully you will have none or very little. If all is well so far, then try with an old speaker and a source to see if it makes music - hopefully it will! (remember, only hookup and disconnect sources and loads with it turned off)At least we would then know if one or both channels need work.
I'd hold off buying parts until you know exactly what you need. For example, if the 2n5876's are shot, they are going to be tough to source. If it were me and that was the case, I would then seriously consider fitting the whole amp with new Motorola MJ series parts and keeping the good 2n parts as spares for your other amp. Food for thought...
Keep us posted.