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Old 4th January 2013, 10:41 PM   #51
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Quote:
Originally Posted by badraven View Post
I'll do what I need to do. The amp is broke so it just experience for me at this point. Can you identify the "Driver Circuit" for me or are you saying to pull and check every piece on the board? Thanks!

BR
I would first replace output transistors then fire up the amp with a lamp in series with the mains. A 40 watt lamp is fine.
If the lamp comes on then there is another fault to fix.
If not try it with some music.
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Old 4th January 2013, 10:42 PM   #52
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Default nigelwright7557

Sounds like a solid plan to me.

BR
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Old 4th January 2013, 11:02 PM   #53
JMFahey is offline JMFahey  Argentina
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DigiKey has 3 of them, only missing 2sc3298.
Keep googling fot parts suppliers.
Avoid NTE and EBay, search "serious" suppliers as Digikey, Mouser, etc.
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Old 4th January 2013, 11:38 PM   #54
JMFahey is offline JMFahey  Argentina
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Quote:
your output transistors are shorted , replace both oputputs and drivers, meaning Q18/19/20/21 .
And then test as suggested by Nigel.
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Old 5th January 2013, 01:08 AM   #55
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Thanks for the advice. I'm looking. I guess we can take back up in a week or so. Thanks!
BR
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Old 5th January 2013, 08:08 AM   #56
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Originally Posted by nigelwright7557 View Post
Not for a novice but what I do is remove all output transistors ( or disconnect them) and route the driver output back into the LTP and then I can check bias and DC offset without blowing fuses.
Likewise - I often do the same - and quite often run it for a good while like that with a scope on the output and a suitable dummy load (a LOT higher than the speakers impedance).
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Old 5th January 2013, 12:48 PM   #57
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Quote:
Originally Posted by Nigel Goodwin View Post
Likewise - I often do the same - and quite often run it for a good while like that with a scope on the output and a suitable dummy load (a LOT higher than the speakers impedance).
I don't have a scope, although I do plan to get one when the opportunity presents its self.

Can you decipher this for me please. "route the driver output back into the LTP and then I can check bias and DC offset without blowing fuses."

I did a search for LTP Electronics and came uip with all sorts of crazy results.

Please explain this connection your describe and how to test it. Or direct me to where I can find the info I need. That way I will be ready when my parts arrive.

Thanks!

BR
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Old 5th January 2013, 01:10 PM   #58
Enzo is offline Enzo  United States
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"Long Tail Pair" or "differential pair".

In your amp that is Q9 and Q10.
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Old 5th January 2013, 03:12 PM   #59
JMFahey is offline JMFahey  Argentina
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Dear badraven.
I'm trying to make this simple because I think *today* you want to have your amp working.
So I *try* to keep math/tech stuff as little as possible , although of course some is still necessary, and give you "paint by the numbers" instructions.

That amp *is* repairable , but I had a not-too-good experience in another Forum (MEF) where a bunch of us, including our friend Enzo , tried to help a Texan Tech (won't give names) to repair a FM212.

What could have been solved in, say, 10 questions and answers streched for over 100 posts, basically because he did not answer what he was asked , as in "measure Q18 base voltage" and he answered "suspect one cap, pulled it to measure ESR, will probably replace it" which in due course degenerated in a discussion about capacitor dielectric influence on sound, and so on and on and on.

You already measured outputs and drivers, found shorts, fine. Replace them.
Quote:
also check (in the regular 200 ohms scale) that R109/112 are not open.
Your multimeter will probably show a higher value, say 1/2 or 1 ohm, but that's fine, regular multimeters also add their own internal resistance (wiring/cpnnectors/switches/probes) which never is "0", what we don't expect there is "open" or a *large* value , say 10 ohms or more.
Post results.
Then we'll go on

PS: mind you, that Tech I referred to, is a regular Tech, has all kinds of fancy equipment, and knows how to use it, simply can't focus on what he's doing and his mind jumps all over the place, thinking about 10 different things at the same time, instead of concentrating on the specific problem he's solving *now*.
Of course it takes much longer that way

Last edited by JMFahey; 5th January 2013 at 03:17 PM.
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Old 5th January 2013, 03:43 PM   #60
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JMFahey I'm not trying to drag anything out. I think I have provided everything you have asked except for removing the transistors, which you said are shorted and need to be replaced. I figure I will remove them and replace them when the parts arrive. Less chance of losing things if they stay attached.
If however I have missed something please forgive me, I am being tossed a lot of ideas here. You basically said to concentrate on what you are telling me so as to avoid confusion. That is what I am doing but when others say something that peaks my interest I ask them to clarify. I did ask for help here. It would be rude for me to ignore people that seem to be earnestly trying to help. I mean there have been several open ended comments by people tossing a guess into the mix, of which I paid little attention.

I am trying to locate the parts on the Internet right now, including the two site you mentioned. I'm not doing a very good job of finding the parts though.

I did answer your question about R109 and R112 in post 39.


R109 = 0 ohms
R112 = .1 (20 scale)

Again, I am doing what you have said to do.

Thanks!

BR



Quote:
Originally Posted by JMFahey View Post
Dear badraven.
I'm trying to make this simple because I think *today* you want to have your amp working.
So I *try* to keep math/tech stuff as little as possible , although of course some is still necessary, and give you "paint by the numbers" instructions.

That amp *is* repairable , but I had a not-too-good experience in another Forum (MEF) where a bunch of us, including our friend Enzo , tried to help a Texan Tech (won't give names) to repair a FM212.

What could have been solved in, say, 10 questions and answers streched for over 100 posts, basically because he did not answer what he was asked , as in "measure Q18 base voltage" and he answered "suspect one cap, pulled it to measure ESR, will probably replace it" which in due course degenerated in a discussion about capacitor dielectric influence on sound, and so on and on and on.

You already measured outputs and drivers, found shorts, fine. Replace them.

Post results.
Then we'll go on

PS: mind you, that Tech I referred to, is a regular Tech, has all kinds of fancy equipment, and knows how to use it, simply can't focus on what he's doing and his mind jumps all over the place, thinking about 10 different things at the same time, instead of concentrating on the specific problem he's solving *now*.
Of course it takes much longer that way
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