, here's my story with my Altec 9440a.
I bought it from a so-called "friend" who guaranteed that a tech had fully serviced it and it was in top notch shape. Well that wasn't the case.
When hooked up, a obvious and loud buzzing was coming from the speakers. When. The volume was low, almost like a ground loop but wasn't. Then the left channel started to cut out. I had enough of that, so I opened the lid and found the whole output board had a hack job for solder. Resoldered it all, turned it on and no more channel cutting out but still something wasn't right. Let me mention that various other parts have been changed too and whoever did it did not duplicate the same change to both sides of that makes sense to you. Checked DC offset and they were way off. I managed to get the right channel pretty close 0vdc but left channel won't go less than about 28vdc and the knob won't turn anymore.
Now is when things got messed up for because I was an idiot and tried working on it when I was extremely tired and missread the service manual. Please do not yell at me or call me names I already know how stupid I am. I went to adjust the bias with my multimeter by desolderong the wire @ E5 and by running my multimeter in series from saod wire and back into the board. Well, like I said I was an idiot and not paying attention. I connected my multimeter in between E5 and E20, turned on the amp, was so tired that even when the relay was clicking on and off I didn't stop to realize I had done something wrong until the 10a fuse in the back blew.
Now, with new fuses they blow instantly, poking around with the multimeter again, I'm pretty sure I blew A LOT of transistors and probably some diodes on the driver board and output board. The last fuse I put it made a spark come from one of the transistors on the back and then blew the fuse. This transistor has always looked fishy to me anyways. Now my problem is, should I go about desoldering all of the transistors for proper testing because in circuit they mostly all test bad or should I be looking at something else? I should add that the heat sink in the rear became extremely hot when the mistake happened.
I'm not sure how to put photos up from my phone if anyone can chime me in on that. But the schematics and photos are easily found on line and in these forums. Thank you for the help! I really want this amp to work cuz I paid a butt load for it and I really don't want to take it in and pay another fortune to fix it when I can do it
I bought it from a so-called "friend" who guaranteed that a tech had fully serviced it and it was in top notch shape. Well that wasn't the case.
When hooked up, a obvious and loud buzzing was coming from the speakers. When. The volume was low, almost like a ground loop but wasn't. Then the left channel started to cut out. I had enough of that, so I opened the lid and found the whole output board had a hack job for solder. Resoldered it all, turned it on and no more channel cutting out but still something wasn't right. Let me mention that various other parts have been changed too and whoever did it did not duplicate the same change to both sides of that makes sense to you. Checked DC offset and they were way off. I managed to get the right channel pretty close 0vdc but left channel won't go less than about 28vdc and the knob won't turn anymore.
Now is when things got messed up for because I was an idiot and tried working on it when I was extremely tired and missread the service manual. Please do not yell at me or call me names I already know how stupid I am. I went to adjust the bias with my multimeter by desolderong the wire @ E5 and by running my multimeter in series from saod wire and back into the board. Well, like I said I was an idiot and not paying attention. I connected my multimeter in between E5 and E20, turned on the amp, was so tired that even when the relay was clicking on and off I didn't stop to realize I had done something wrong until the 10a fuse in the back blew.
Now, with new fuses they blow instantly, poking around with the multimeter again, I'm pretty sure I blew A LOT of transistors and probably some diodes on the driver board and output board. The last fuse I put it made a spark come from one of the transistors on the back and then blew the fuse. This transistor has always looked fishy to me anyways. Now my problem is, should I go about desoldering all of the transistors for proper testing because in circuit they mostly all test bad or should I be looking at something else? I should add that the heat sink in the rear became extremely hot when the mistake happened.
I'm not sure how to put photos up from my phone if anyone can chime me in on that. But the schematics and photos are easily found on line and in these forums. Thank you for the help! I really want this amp to work cuz I paid a butt load for it and I really don't want to take it in and pay another fortune to fix it when I can do it
It sounds like you have done some serious damage. If you saw a transistor spark then that and others will have fried I'm afraid.
Fixing a monster amp like this isn't just a case of replacing obviously zapped parts, you need to go through it all systematically and also use a current limited supply (such as a bulb tester) to prevent further damage while working on it.
Probably not what you wanted to hear
Fixing a monster amp like this isn't just a case of replacing obviously zapped parts, you need to go through it all systematically and also use a current limited supply (such as a bulb tester) to prevent further damage while working on it.
Probably not what you wanted to hear
Not exactly what I wanted to hear but it was expected. I can't believe it did this I feel like such an idiot. I was thinking if using a dim bulb but a 1000w or higher bulb is gonna be hard and expensive to obtain. I currently have no more fuses so I'm doing what I can before I need to send it in. Caps and resistors all seem to be ok, it's just the transistors that don't. What are some more steps I should be taking? I havent worked on anything this big before and I'm way to poor to pay someone thousand of dollars to do it for me. Thank you for any help, if I am absolutely screwed after everything that I can try I will go another route. I was looking at transistors to order and it seems like a lot of them are obsolete.. but I've also read that transistors can easily be replaced with one of the same value.. any input on this? My head is spinning trying to get this going again.
but I've also read that transistors can easily be replaced with one of the same value.. any input on this? My head is spinning trying to get this going again.
As you started a new thread I've moved my reply and yours here and deleted those from the other thread.
Fixing any amp that has major damage requires thought and planning. The parallel transistors all need to be (ideally) matched or at the very least from the same batch which means replacing them all.
The amp can be worked on with just one poor of devices fitted.
Fixing any amp that has major damage requires thought and planning. The parallel transistors all need to be (ideally) matched or at the very least from the same batch which means replacing them all.
The amp can be worked on with just one poor of devices fitted.
what can I say , except to repeat what I wrote several times:
- most convenient and clever way of repair , for person not doing that every day for living , is systematic and slow approach: check each semiconductor first with diode test and - if anything is suspicious - desolder it from pcb and check outboard - either with diode test or with (nowadays cheap and affordable) do-it-all-component-tester ; you can find them everywhere for 20 or so greenies
if you're in doubt about (changed) type of semi , ask here
check any suspiciously looking resistor; lift one leg if needed
if there were burned components around any trimpot , change trimpot to new one ; multiturns are easier to play with than old ones , anyway
after patient and thorough check of everything , if you're unsure of any step in setting procedure , write here
last but not least - proceed with entire adventure only if you're sure in gaining anything with that , be it "just" learning , or having an amp for your exact needs ; if there is any doubt in that - just forward it to someone else who will have some gains
edit : what I wrote - I meant on channel pcbs ; of corse same applies to output transistors - check them all , same logic
always do checking of just one component out of place , and take tons of pics while working ..... that will save you of mix-ups
- most convenient and clever way of repair , for person not doing that every day for living , is systematic and slow approach: check each semiconductor first with diode test and - if anything is suspicious - desolder it from pcb and check outboard - either with diode test or with (nowadays cheap and affordable) do-it-all-component-tester ; you can find them everywhere for 20 or so greenies
if you're in doubt about (changed) type of semi , ask here
check any suspiciously looking resistor; lift one leg if needed
if there were burned components around any trimpot , change trimpot to new one ; multiturns are easier to play with than old ones , anyway
after patient and thorough check of everything , if you're unsure of any step in setting procedure , write here
last but not least - proceed with entire adventure only if you're sure in gaining anything with that , be it "just" learning , or having an amp for your exact needs ; if there is any doubt in that - just forward it to someone else who will have some gains
edit : what I wrote - I meant on channel pcbs ; of corse same applies to output transistors - check them all , same logic
always do checking of just one component out of place , and take tons of pics while working ..... that will save you of mix-ups
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I'll have to leave it for now but I suspect this is going to outside your comfort zone. The amp draws only a minimal current when idling and during repair you would alter the biasing to make that even lower... so a low wattage bulb would be fine.
Obsolete semiconductors are always a big problem because there are so many fake and remarked parts around... don't buy semi's off auction sites as a general rule. That means using new and modern parts and the circuit may need minor tweaks to use those successfully... and oscilloscope is really required to look for stability issues in that case.
Obsolete semiconductors are always a big problem because there are so many fake and remarked parts around... don't buy semi's off auction sites as a general rule. That means using new and modern parts and the circuit may need minor tweaks to use those successfully... and oscilloscope is really required to look for stability issues in that case.
Thank you. I unfortunately don't have scope, yet. Which really sucks so I can only do so much. Nothing is burnt, no smoke came out, just a the little spark. I know it is not a good thing at all. Diodes seem to all pass current correctly on the meter. The xsistors on all of the "Q" joints are not reading correctly. Should I remove them for a more thorough test? I know I'm an amateur at best but wouldnt bad driver / output transistors immediately blow the fuse upon start up?
How can I use my meter to find out which way the bias knob is going (up or down) obviously I can't turn it on but would like to know.
How can I use my meter to find out which way the bias knob is going (up or down) obviously I can't turn it on but would like to know.
seriously - if you are not able to understand (and do) everything I wrote in post #5 - either leave an amp aside as long you need to collect more experience , or do it with some help- paid or not
it's much worse being stubbornly ignorant and making a mess , than realizing own low level of expertize
I'm good with amps , but lousy in so many other things ......
it's much worse being stubbornly ignorant and making a mess , than realizing own low level of expertize
I'm good with amps , but lousy in so many other things ......
Thanks for the help. I know I'm no expert but Im trying to learn as much as I can. With some guidance hopefully I can atleast find out what's wrong. Not saying I have the capability to fix it unless it just an easy exchange of part. I do not plan on sending any power whatsoever to it until a professional does. But checking simple small components like resistors and caps etc I'm mostly capable of doing. I just don't know exactly what every piece of the puzzle does, I have a little bit of an understanding though after as much research on the amp as I've been able to find so far.
Power transistors generally fail by going short circuit from C to E. That at least can be checked in circuit. All output transistors and all driver transistors need that first basic check first.
All those 0.5 ohm resistors need checking. Have any gone open circuit.
I have to agree with 6L6 and Zen Mod and that without a basic understanding and experience you stand a good chance of making things worse.
By just looking at the circuit diagram. Q9 needs to be fully on to give minimum bias. Forget CW and CCW as it is to open to interpretation and error. Is that viewed from the back or the front of the board and so on.
To force minimum bias, the preset has to be at maximum resistance.
Have a read at this still current thread which isn't going to well despite step by step instruction (and if you read it through to the end you will see why) to see just how fraught with difficulty something like this can be.
Marantz PM66KI amp - resistor keeps dying!
All those 0.5 ohm resistors need checking. Have any gone open circuit.
I have to agree with 6L6 and Zen Mod and that without a basic understanding and experience you stand a good chance of making things worse.
By just looking at the circuit diagram. Q9 needs to be fully on to give minimum bias. Forget CW and CCW as it is to open to interpretation and error. Is that viewed from the back or the front of the board and so on.
To force minimum bias, the preset has to be at maximum resistance.
Have a read at this still current thread which isn't going to well despite step by step instruction (and if you read it through to the end you will see why) to see just how fraught with difficulty something like this can be.
Marantz PM66KI amp - resistor keeps dying!
I have repaired one that I use every day driving 4 PA-boxes (with RCF 12 inch and 1 inch drivers) in ny workshop.
It has no problem to play for the whole neighborhood.
One reason why I made it was that I had a non working amp as spare parts and a bunch of extra transistors.
There's lots of pitfalls here, every part has to be checked and changed if they're out of specs.
Capacitors in feedback circuit are another sensitive thing I notised, and the thing that most parts are EOL since many years ago does not make things easier.
Maybe I wasn't experienced enough on amps but I'm experienced in troubleshooting and had a lot of time then.
Now I'm very pleased with the sound and 2x400w make it rock stable in bass.
BR
Figge
It has no problem to play for the whole neighborhood.
One reason why I made it was that I had a non working amp as spare parts and a bunch of extra transistors.
There's lots of pitfalls here, every part has to be checked and changed if they're out of specs.
Capacitors in feedback circuit are another sensitive thing I notised, and the thing that most parts are EOL since many years ago does not make things easier.
Maybe I wasn't experienced enough on amps but I'm experienced in troubleshooting and had a lot of time then.
Now I'm very pleased with the sound and 2x400w make it rock stable in bass.
BR
Figge
Alright a new approach. Been doing lots of research and not giving up yet. All output transistors have been tested. Here's the results. I had to do it in a way I could understand. My poor attempt at drawing would be as looking at the board from the backside as in the picture of the board itself.. I hope this makes sense. Umm how can I upload pictures from my phone?
Disregard the pic I tried to upload. It was wrong. I wiill post the right one.
Pictures won't upload for some reason will try again later. So far most out the power transistors from Q2-Q14 measure open all ways. Good call on the 0.5ohm resistors. I decided to remove all transistors to get to the back of the board and yup, they are blown. I've been talking to a tech that I found local, unfortunately he's out of town for the week but is going to do a bit of searching for replacements the 120392's. I haven't been able to even see any modern replacements made after 1999. But then again I don't really know where to look. Any other input is appreciated.
Pictures won't upload for some reason will try again later. So far most out the power transistors from Q2-Q14 measure open all ways. Good call on the 0.5ohm resistors. I decided to remove all transistors to get to the back of the board and yup, they are blown. I've been talking to a tech that I found local, unfortunately he's out of town for the week but is going to do a bit of searching for replacements the 120392's. I haven't been able to even see any modern replacements made after 1999. But then again I don't really know where to look. Any other input is appreciated.
Unfortunately we are passed that point. But yeah they were all loose when this thing went haywire. Dont forget it was my fault it went bazurk, not the amps.
0.5ohm resistors measure around 1.5 and a couple have burnt marks under them.
Both output boards are the same for blown resistors. Finally at least a little more that I can go off of.
Going to save up and replace all 0.5ohm resistors, I've been able to track down replacement power transistors (MJ15024 and 2n6259) for the 120392 and for the 120226 I can look for 2n3584 120157 2n6421. I will also change out the driver board caps.
While I wait to afford all this I'll build a dim bulb tester and try to get my hands on a scope. I will also get my tech to look it over before any power ever goes to it. The control board seems to be unharmed and I don't think the relay or anything like that was affected either. Praying that changing out all bad parts will get it alive again. Wisful thinking maybe, but at least I have some help now.
0.5ohm resistors measure around 1.5 and a couple have burnt marks under them.
Both output boards are the same for blown resistors. Finally at least a little more that I can go off of.
Going to save up and replace all 0.5ohm resistors, I've been able to track down replacement power transistors (MJ15024 and 2n6259) for the 120392 and for the 120226 I can look for 2n3584 120157 2n6421. I will also change out the driver board caps.
While I wait to afford all this I'll build a dim bulb tester and try to get my hands on a scope. I will also get my tech to look it over before any power ever goes to it. The control board seems to be unharmed and I don't think the relay or anything like that was affected either. Praying that changing out all bad parts will get it alive again. Wisful thinking maybe, but at least I have some help now.
If all the 0.5 ohm measure 1.5 ohm then that could indicate a measurement error. Measuring low values requires both a good meter and also you subtracting the meters own lead resistance from the result. If you short the meter probes together you should see 0.00 ohms but will invariably see some other result due to lead resistance.
For initial test purposes this amp should run with a single pair of drivers and a single pair of outputs fitted. That makes working on it a whole lot easier.
All those 1 ohm and 4.7 ohm resistors need checking as well.
For initial test purposes this amp should run with a single pair of drivers and a single pair of outputs fitted. That makes working on it a whole lot easier.
All those 1 ohm and 4.7 ohm resistors need checking as well.
Yeah well since most of the .5 were blown up I'm gonna replace them all anyways. Very well could be 1ohm lead resistance but it does not hurt to change them all. Next up will checking the rest of the resistors on the output board. I'm hoping I don't need to do much on the driver board as that's a lot of soldering lol. I don't mind changing all the resistors as that's cheap and fairly easy. Then move on to caps. Cheers! Pretty sure the main caps have been recently enough changed which would be nice but I'll check them too. Need to get a capacitance meter now.
Keeps freezing when I try to upload photos or I would be
Keeps freezing when I try to upload photos or I would be
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