Jump to content
Sign in to follow this  
Caelum

Fried transistors in PSU of Stereo amp

Recommended Posts

Ok...

 

Got a bloody good quality stereo amp sitting here, that needs fixing.

 

 

Me and my old man have gone through and found the suspect failed components - two transistors, one or both of which have gone short circuit, and then also fried three resistors and maybe a cap as well. (we have circuit diagrams, my old man is an electrical engineer and me a hobbyist, so are confident in our findings)

 

We can replace(and have parts to replace) the resistors and cap, but we can't find any currently manufactured components of these two transistors, or equivalents thereof.

 

2sc1775a

2sd669a

 

One is low noise amplifier transistor, and the other is a pass transistor for the main power supply.

Both are/were made by hitachi/renesis.

 

 

Anyone have any information that would lead to me being able to purchase these two components?

 

It would likely cost me several hundred dollars(i'm guessing between 200 and 500) in order to get this fixed by a service center, assuming they even are able to - my research has come up blank on where i could buy these two Q's from.

 

Total worth of the amp in new condition is $1750...

 

 

 

 

Anyone provide any help for me?

Share this post


Link to post
Share on other sites

Cheers, will use that as a backup.

 

Also sent an email to worcom, in perth, who i hope will be able to help out.

Share this post


Link to post
Share on other sites

tried farnell and RS, no joy.

 

 

(tried before posting here)

 

 

 

digikey, mouser have neither that i'm after, prime has the 2sd669a, but not the 2sc1775a.

 

worcom suggested i contact westec, and they told me that they had the 2sd669a on their price list, but not in stock, and the 2sc1775a didn't exist on their lists at all.

 

Looks like robzy's mainelectronics link will be the best option.

Edited by Caelum

Share this post


Link to post
Share on other sites

http://www.cricklewoodelectronics.co.uk/Cr...=178&page=4

They have the 2sc1775a and equivalent of 2SD669A

http://www.cricklewoodelectronics.co.uk/Cr...at=0&page=1

 

I think that's what they indicate.

 

Ok Caelum, I'll bite too.

 

What is this "bloody good quality stereo amp sitting here" ?

 

:)

 

Edit:refer to post lower down for the other one (cheers Rob)

Edited by datafast69

Share this post


Link to post
Share on other sites

So is it an alternative?

Afraid not.

 

To have a quick stab at what a "complement" is: If you're designing a push-pull output stage (on an amplifier, say) you need to use two transistors - one to "push" and one to "pull". One would be an NPN and one would be a PNP.

 

It's not a great way of thinking about it, but an NPN transistor needs electrons sucked out of it's base in order to conduct, while a PNP transistor needs electrons forced into it's base in order to conduct. (I think)

 

For the output stage, though, you want both the "push" and the "pull" transistors to have similar characteristics - so you need to use a complement pair of an NPN and PNP transistors that are purposely made to have similar (albeit, reversed) characteristics.

 

(Sorry to thread crap Caelum)

 

[edit]: Actually, ignore all the above if it makes no sense, it can be summarised pretty succinctly as: A complement pair are two transistors that have similar - albeit, in a way, reversed - characteristics.

 

Oh, and good google-fu you have going there :P

 

Rob.

Edited by robzy

Share this post


Link to post
Share on other sites

Yeah, I understand the meaning of the word.

 

It's just that it came up with that one when I used the search function on that site, but as you can see they do have it, I just had to find it manually.

 

Edit: "google-fu" Rob?

 

I like it :D needs to be added to some dictionary somewhere ;)

Edited by datafast69

Share this post


Link to post
Share on other sites

Yeah, I understand the meaning of the word.

 

It's just that it came up with that one when I used the search function on that site, but as you can see they do have it, I just had to find it manually.

Ah, my bad, didn't mean to be condescending or anything. Perhaps someone else will benefit from the quick explanation? :P

 

Rob.

Share this post


Link to post
Share on other sites

Yeah, I understand the meaning of the word.

 

It's just that it came up with that one when I used the search function on that site, but as you can see they do have it, I just had to find it manually.

Ah, my bad, didn't mean to be condescending or anything. Perhaps someone else will benefit from the quick explanation? :P

 

Rob.

 

LOL

Tis OK Rob :)

 

I liked reading the response all the same :)

 

Yes Caelum! Brand & Model please ;)

 

Please don't say something like Sherwood or Silver :(

Share this post


Link to post
Share on other sites

Definitely worth fixing.

 

For the cost of a few components, even more so :)

 

Edit:Can I ask what speakers are running off it?

 

I can't help myself, all this interests me :)

Edited by datafast69

Share this post


Link to post
Share on other sites

Yeah, a less capable amp would have some issues i'd say, but the NAD handles it like a charm.

 

 

Interestingly, the fault on the NAD that i'm now fixing happened while the amp was sitting idle... random component failure it seems, so it wasn't even in use at the time, let along working hard...

Share this post


Link to post
Share on other sites

That's the general feeling I have formed around NAD as a brand, they make some pretty good amps at times but the failure rate seems to be a little on the high side. Though that may just be a few isolated models...

 

The well received and still traded often 3020, seemed to blow up on many a user, maybe not in the shot term but eventually. That's if my memory serves me right...Maybe they run some of these biased to near there limits?

 

Edit:Just thinking about the 3020's and I think with them it was the PSU that were apt to die in them...hmm...

Edited by datafast69

Share this post


Link to post
Share on other sites

Is the PSU on a separate board and how much room is in the case?

 

ie. can you maybe use another PSU to deliver the same voltages?

Share this post


Link to post
Share on other sites

Deleted

 

Edit:Never mind me, I'm sleep deprived again :P

 

So much that I had to use a different descriptive word because I couldn't work out to spell the other one :(

Edited by datafast69

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×