Clem, I know the feeling with all the fakes. Can you tell me a few brands that have good quality stuff (assuming they are not fakes?).
Audiolabs out of GA has some to offer for about 4 bucks or so each. They are not NTE which I definitely do not want this time around just in case.
I will check the output to ground tonight.
Another wierd thing. One of the sanken devices that is bad has funny looking silkscreening on it. I wonder if its a fake.
Evan
Audiolabs out of GA has some to offer for about 4 bucks or so each. They are not NTE which I definitely do not want this time around just in case.
I will check the output to ground tonight.
Another wierd thing. One of the sanken devices that is bad has funny looking silkscreening on it. I wonder if its a fake.
Evan
Good probability on fake parts there - My brother attempted to fix an Onkyo power amplifier some time ago, but the output transistors kept blowing up. It would work perfectly on the bench for a whole day with a series lamp, but after putting it into service, it would "poof" in a few days. He finally gave up on it as we figured it was simply a case of having fake output transistors, and we couldn't source any genuine stuff.
Oh, well I guess if we really DID try to find original stuff (i.e. ask friends overseas, or order via Internet) we might have, but the amplifier circuit/topology wasn't worth it...
Cheers!
Clem
Oh, well I guess if we really DID try to find original stuff (i.e. ask friends overseas, or order via Internet) we might have, but the amplifier circuit/topology wasn't worth it...
Cheers!
Clem
Clem, the resistance across the terminals gives me about 1.375 on the 2M ohm setting of my meter. Does this sound pretty normal? Resistance is obviously MUCH less with my other amp that still has all its outputs in place.
Evan
Aparently there is no protection relay because i pulled that reading right off of the terminals.
Evan
Aparently there is no protection relay because i pulled that reading right off of the terminals.
Hi Evan -
I meant to check for 0utput offset voltage - so your VOM should be set to measure DC voltage, with the power applied to the amp. If your driver transistors are working properly the offset voltage should be pretty close to zero. On the other hand if its totally zero, that wouldn't be good either, since that would mean something is "open". It certainly seems that way if your resistance measurement is 1.375M ohms!!
Cheers,
Clem
I meant to check for 0utput offset voltage - so your VOM should be set to measure DC voltage, with the power applied to the amp. If your driver transistors are working properly the offset voltage should be pretty close to zero. On the other hand if its totally zero, that wouldn't be good either, since that would mean something is "open". It certainly seems that way if your resistance measurement is 1.375M ohms!!
Cheers,
Clem
Thanks clem, your teaching me alot here!
DC offset is .005 vdc
Now some amps are cap coupled at the output so they measure a pretty consistent bias voltage no matter whats going on right? I think this amp may be that type if you look at the pics of the board on the inside there are four wima caps that I think bridge from + to - but this is just a guess.
Thanks - Evan
DC offset is .005 vdc
Now some amps are cap coupled at the output so they measure a pretty consistent bias voltage no matter whats going on right? I think this amp may be that type if you look at the pics of the board on the inside there are four wima caps that I think bridge from + to - but this is just a guess.
Thanks - Evan
Hi Evan,
Those capacitors are most probably the power supply filters, not for output coupling. Your amp is likely to be direct-coupled at the output, it would be a waste to add another capacitor since the amp already is working on split (+-) supplies!
0.005 volts should be ok. If the amp is truly working properly, you can even connect your speaker to it and give a listen - it should work, though keep the volume as low as possible, just enough to hear the amp, and keep the test as short as possible (i.e. a few seconds of listening). Note - I mean you can listen to it without reconnecting ANY of the output transistors.
Assuming that works, confirm that the bias works properly, turn it down and purchase and install your output transistors...
Cheers,
Clem
Those capacitors are most probably the power supply filters, not for output coupling. Your amp is likely to be direct-coupled at the output, it would be a waste to add another capacitor since the amp already is working on split (+-) supplies!
0.005 volts should be ok. If the amp is truly working properly, you can even connect your speaker to it and give a listen - it should work, though keep the volume as low as possible, just enough to hear the amp, and keep the test as short as possible (i.e. a few seconds of listening). Note - I mean you can listen to it without reconnecting ANY of the output transistors.
Assuming that works, confirm that the bias works properly, turn it down and purchase and install your output transistors...
Cheers,
Clem
Clem, went ahead and ordered the outputs. I will need them some point anyways.
I attempted to get sound from the amp. It was very very distorted and i had to really crank my source to get sound. I powered the amp off and felt the transistors that are above the drivers. On the - rail (left side on the pics) the transistors were warm but nothing but just warm. The positive rail had one transistor that got HOT and another that was pretty much cold. I am wondering if that is an underlying problem. I have not pulled them from the circut yet but will because the one got warm enough for me to pull my hand away (but not hot enough to burn) and it got hot quick. I did not have signal to that amp for more than 10 sec, and could hear sound for about 5.
Thanks clem, you are SO helpful.
I assume that the outputs are part of the problem and there is still some funkiness going on. I was supposed to get clean/clear sound right?
Evan
I attempted to get sound from the amp. It was very very distorted and i had to really crank my source to get sound. I powered the amp off and felt the transistors that are above the drivers. On the - rail (left side on the pics) the transistors were warm but nothing but just warm. The positive rail had one transistor that got HOT and another that was pretty much cold. I am wondering if that is an underlying problem. I have not pulled them from the circut yet but will because the one got warm enough for me to pull my hand away (but not hot enough to burn) and it got hot quick. I did not have signal to that amp for more than 10 sec, and could hear sound for about 5.
Thanks clem, you are SO helpful.
I assume that the outputs are part of the problem and there is still some funkiness going on. I was supposed to get clean/clear sound right?
Evan
Hi Evan,
If the circuit up to the drivers were ok, the sound should have been clean, though you wouldn't be able to pull any decent volume from it and the amp would start distorting. If its distorted all the way even at very low volumes, something ain't working.
Could you put a circle on the transistors you said got very hot (and the other stayed cool) and post... Could be that the cold transistor is bad or isn't biased properly...
Cheers!
Clem
If the circuit up to the drivers were ok, the sound should have been clean, though you wouldn't be able to pull any decent volume from it and the amp would start distorting. If its distorted all the way even at very low volumes, something ain't working.
Could you put a circle on the transistors you said got very hot (and the other stayed cool) and post... Could be that the cold transistor is bad or isn't biased properly...
Cheers!
Clem
Clem, here is a photo/description of what I am dealing with here.
From what I traced on the boards these were the transistors actually driving the output of the amp at the time. Am I right in this conclusion? I can take a clearer pic if you need me too.
Thanks buddy - Evan
I really did not get ANY volume to speak of. Mostly spitty distortion consistent with a messed up amp LOL.
From what I traced on the boards these were the transistors actually driving the output of the amp at the time. Am I right in this conclusion? I can take a clearer pic if you need me too.
Thanks buddy - Evan
I really did not get ANY volume to speak of. Mostly spitty distortion consistent with a messed up amp LOL.
Attachments
Clem, sounds good man.
Yes the one on the right was stone cold, the one on the left was cookin
I have them both out of circut right now, I am unsure how to properly test a drain/gate/source piece. I tested all the components directly linked to these and the resistors etc.. all test good.
Have a good class!
Evan
Yes the one on the right was stone cold, the one on the left was cookin
I have them both out of circut right now, I am unsure how to properly test a drain/gate/source piece. I tested all the components directly linked to these and the resistors etc.. all test good.
Have a good class!
Evan
Hi Evan,
http://www.uoguelph.ca/~antoon/gadgets/mostest.htm
has something on testing a MOSFET. But I really find it wierd that drivers would be MOSFET devices and outputs are BJT?!
If the other driver was stone-cold it could be bad...
Cheers!
Clem
http://www.uoguelph.ca/~antoon/gadgets/mostest.htm
has something on testing a MOSFET. But I really find it wierd that drivers would be MOSFET devices and outputs are BJT?!
If the other driver was stone-cold it could be bad...
Cheers!
Clem
Clem, I attempted to test these using the technique on the site but do not think my meter is capable of testing it properly.
I can order a new pair for 8 dollars + shipping. I am to the point where I cannot imagine another source of the problem. What are your thoughts? I am now past the stage of "throwing parts at it" to get things to work LOL.
Evan
Next time I am in manilla, (who knows!) I owe you a drink LOL.
I can order a new pair for 8 dollars + shipping. I am to the point where I cannot imagine another source of the problem. What are your thoughts? I am now past the stage of "throwing parts at it" to get things to work LOL.
Evan
Next time I am in manilla, (who knows!) I owe you a drink LOL.
Hi Evan,
Tell you what - can you get good, complete pictures of the top and bottom of the driver board, head on (like, put the board at your feet and shoot the camera straight down). Then label the transistors, then e-mail the pics to me ( ongc at dlsu dot edu dot ph ) . Lets see if we can manage to generate a proper schematic, before blowing any more bucks into the thing!
Cheers,
Clem
ps: as for the drink - sure, or maybe if I'm ever back in the US eh...
Tell you what - can you get good, complete pictures of the top and bottom of the driver board, head on (like, put the board at your feet and shoot the camera straight down). Then label the transistors, then e-mail the pics to me ( ongc at dlsu dot edu dot ph ) . Lets see if we can manage to generate a proper schematic, before blowing any more bucks into the thing!
Cheers,
Clem
ps: as for the drink - sure, or maybe if I'm ever back in the US eh...
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