NAP-140 Clone Amp Kit on Ebay - Page 108 - diyAudio
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Old 19th January 2013, 06:41 PM   #1071
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Quote:
Originally Posted by Ruwe View Post
By the way, hearing radio is very bad sign. Something is very wrong with your amp.
It goes away when I moved my hand over the board so I was thinking that it's picking up RFI from somewhere.
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Old 19th January 2013, 06:51 PM   #1072
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Originally Posted by Ian Finch View Post
The original Naim parts are ZTX653/753 from Diodes Inc. Mouser sell them for $1 or so. Unfortunately, there are no cheap and easy substitutes there that supply the current at the speed and voltage.
$1 part is in cheap category IMO.
I'll report back in a few days on bulb test. Thanks for the info.
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Old 20th January 2013, 08:43 PM   #1073
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Default Misprint on board

I discovered a few problems.

C1 and C5 were connected wrong. Photo on ebay is correct but the board received is reversed (misprint).

Q3 and Q7 were connected wrong. Again, misprint on board.

I'm not sure why they do that. To avoid copyrights maybe? They could have noted that in the instruction or something. Such is the risk of buying cheap stuff on ebay...
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Old 20th January 2013, 09:31 PM   #1074
Ruwe is offline Ruwe  Europe
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Originally Posted by Evenharmonics View Post
C1 and C5 were connected wrong. Photo on ebay is correct but the board received is reversed (misprint).
Q3 and Q7 were connected wrong. Again, misprint on board.
The polarity of C1 and C5 is best determined experimentally. Normally, it doesn't matter, and it would not affect the amp operation that much.
If Q7 is wrong then Q8 is probably also wrong. Both are in the protection circuit though. You can omit them altogether, during test and afterwards, if you don't need output protection. They kind of affect the sound quality as well.
Q3 is really a big problem, because it will put the amp output in disbalance (huge DC voltage at the output, like in your case). I hope the drivers and the output transistors survived.
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Old 21st January 2013, 12:12 AM   #1075
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Originally Posted by Ruwe View Post
If Q7 is wrong then Q8 is probably also wrong. Both are in the protection circuit though.
Q8 is printed correctly. Bottom side of board shows the connections right. I noticed that couple areas have been altered compared to online picture. Again, this may be due to copyrights.
Quote:
I hope the drivers and the output transistors survived.
I checked with my DMM but sounded ok. Is there other ways to check them?
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Old 21st January 2013, 04:18 AM   #1076
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Originally Posted by Evenharmonics View Post
Again, misprint on board.......I'm not sure why they do that. To avoid copyrights maybe? They could have noted that in the instruction or something.....
Possibly, it's just as in the past, where the board is only correct for the parts used when it was drawn up. Maybe they were ZTX653/753 for Q4,6. Later, packagers can't buy them cheap enough to be competitive and substitute Chinese 2SD647/D667 which work OK, but like I have said over and over - check the pinouts. You download datasheets to verify what they are in case just Googling "2SD667 pinout" or "2SD677 connections" for example, doesn't bring a quick response from the net.

Should there be problems like this? Well, here we are buying from Ebay stores and this thread is about the issues we endure in dealing with those sellers just to buy ultra cheap - if we are awake to them! I've learned from long-term experience only to buy from trusted sellers who have gained a good reputation - on Ebay or anywhere.

Sellers (Ebay stores) mostly buy the kits from packagers who just fill the bag with whatever suitable parts they can buy cheap. They obviously don't bin thousands of boards when they run out of part X and printing advice of changes usually confuses as much as informs DIYs since the distribution and languages are global. It falls to the seller who isn't always on the ball with his products or service. They could be operating entirely from a bedroom whilst good ones may even email late details with invoice and schematic but do we always check our email?

Sure, there are several different kits and PCBs, but apparently, a lot more sellers with the cheapest possible problem kits and lack of understanding than you can imagine. I'm afraid it's "caveat emptor" and we can only offer suggestions based on what you discover about your particular product.
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Old 21st January 2013, 05:50 AM   #1077
Ruwe is offline Ruwe  Europe
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Originally Posted by Evenharmonics View Post
I checked with my DMM but sounded ok. Is there other ways to check them?
You can give them the standard junctions test with the DMM set to "diode check". If you don't know how, you can google it. Usually that's enough. The transistors should be not in circuit for proper testing. Very seldom transistor that passes the junctions test will still be faulty. I've seen many, but never in audio circuits.
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Old 21st January 2013, 06:06 AM   #1078
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BTW, who was the seller, Evenharmonics? It wouldn't surprise me that the pic. was just copy/pasted from another site to save the effort. Some sellers now add a watermark for that reason. The problems for any buyers using the pic as an assembly guide are obvious, as you find.
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Old 21st January 2013, 03:21 PM   #1079
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It was zoe_tsang.
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Old 22nd January 2013, 12:23 AM   #1080
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Originally Posted by Evenharmonics View Post
It was zoe_tsang.
Thanks, I can't tell on that NAP140c image, but several other images already have logos and watermarks I've seen from other suppliers. Hmm...!

Well, is the board signed LJM as in the the pic? If that is the same, this is possibly the most common kit available and is likely OK, as ljm_ljm is a member here on DIYaudio and has posted some of his PCB revisions in this thread even. I have seen several of his NAP140 boards assembled by local kids and they work fine, when the correct parts are supplied. (Yes, I have seen the wrong parts supplied without notice too, so I keep a small stock of the small signal parts to help out.)

However, if there is an issue with his board marked with the same part numbers as those supplied, I suspect the problem is with the part itself or your reading of the connections.
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