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Please help me to understand

rickb119

rickb119

AK Subscriber
Subscriber
I recently purchased a B&K ex4420 online, and quickly discovered that it has a problem. With everything connected (correctly) the volume is very low. To the point that the volume on the pre (tried 2 different ones) needs to be at max to get a low normal listening level.

I took it to my tech and he tells me that the output mosfets are bad. How can outputs be bad and still pass signal? What sound that is there is good, just very, very low. He said that measured output, with proper input gain, is only 20W.

If it is indeed the outputs that are bad, does anyone know where I can get replacements. My tech asked me to look into it as he doesn't own a computer. A smart phone, but not a computer. He's an older, retired gentleman.

The outputs are SK 1058 and SJ 162. I tried looking online but couldn't find much, other than the auction site which are very pricey. Any help would be greatly appreciated.

The seller did refund the purchase price.
 
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I'm glad you were able to get your money back.

Unfortunately those chips are not made anymore, so you it will have to be a search and a little luck if you want to try to track them down. There are a few reasons that you could still be getting signal, but my guess is that they are not all toast and you are getting power from the few that are still functioning and while the others while not working, are still allowing signal to pass through them hence you have some volume.

If you do want to try to track them down a good first step would be to put a wanted ad on here in barter town that you're looking for them, you may get lucky. Other than that the Bay or calling around to audio techs would be the next step I'd take.

Good luck.
 
avionic said:
B+D Enterprise sells nothing but legit semiconductors.
Hitachi(Renesas) Lateral MOSFET

https://www.bdent.com/nsearch.html?catalog=yhst-864421581610834172249761&query=2SK1058
https://www.bdent.com/nsearch.html?...ze=15&storeid=yhst-864421581610834172249761/1
Click to expand...
Thank you.

I'll see if my tech can pinpoint the problem, rather than just saying "it's the outputs" and wanting to replace them all. The shotgun approach may be easier (for him), but much too pricey for me. For the cost of 20 mosfet's and his labor I can buy a better, working amp.

I'll probably pay him for the evaluation and simply look for a different amp.

Thank you again for the links. Got it bookmarked for future reference. :thumbsup:
 
petehall347 said:
you sure it uses 20 outputs ? its rated at 350 watts 4 ohms .i would expect 8 outputs
have you turned up the controls on the rear panel and switched to unbalanced ? that's assuming its an unbalanced input you are using .
the manual is here ...https://manualzz.com/doc/745863/bandk-ex4420-specifications
Click to expand...

I have the service manual (at least what ATI sent me) for the reference model, which shows 5 each per channel. I assume the ex has the same number, but could be wrong. There are no external controls on this one, and I did try the balance/unbalance switch. It only made a very slight, barely noticeable difference. That was actually my first thought, because of what the user manual (have it) stated about low volume. Still wondering if there might not be a problem with that switch. I'll call the tech tomorrow and ask if he can try using the balanced inputs. If that works, then it's probably the switch. One can hope.
 
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