B&K EX4420

[preston1000]

My B&K EX4420 seems to have a problem with the left channel. The right channel always sounds more detailed and louder than the left channel.

I hope it's an easy fix, well fixable at least without having to take it to someone.

Does anyone have any idea what would cause this and or if someone could point me to a service manual for this amp?

I would appreciate any help I can get on this matter.

 

[Binkman]

Greetings; owners manual indicates in troubleshooting; channel low in output or distorted = blown rail fuse. (could also mean a failing rail fuse not conducting. very possible is 'weak' and this symptom has shown up a few amps on a.k..)
https://www.manualslib.com/manual/14276/BAndk-Two-Channel-Amplifier-Ex4420.html?page=14#manual

Perchance the ex420 schematic is viable. Internal pics of both show different layout but both are rated similar/same wattage? No luck finding 4420sm, though.
bink

 

[preston1000]

Greetings; owners manual indicates in troubleshooting; channel low in output or distorted = blown rail fuse. (could also mean a failing rail fuse not conducting. very possible is 'weak' and this symptom has shown up a few amps on a.k..)
https://www.manualslib.com/manual/14276/BAndk-Two-Channel-Amplifier-Ex4420.html?page=14#manual

Perchance the ex420 schematic is viable. Internal pics of both show different layout but both are rated similar/same wattage? No luck finding 4420sm, though.
bink

Thanks for the link Binkman.
The good news is it's not the B&K amp as I opened it up last night and everything seemed to check out. Ends up being the Sansui AU-717 is the culprit. I switched the output ICs and the problem was reversed. That makes me happy as I was about to find someone local to check out the B&K amp, didn't want to do that.
As for fixing the Sansui, hopefully it just needs a little Deoxit on the L and R balance.

 

[FootFungus]

Check the separate switch on the back of the Sansui as well for good measure.

 

[preston1000]

Check the separate switch on the back of the Sansui as well for good measure.

Will do sir.

 

[preston1000]

The Sansui is fixed. Deoxit red followed by green in the balance, bass and treble pots. Followed with Deoxit gold on the RCAs and man oh man, does it sound incredible.

I should of taken some pictures to show others where to put the Deoxit into the pots. Don't try putting it on the shaft and expect it to work itself down into the pots.

 

[preston1000]

Well not so fast sonny, there's more work to be done. Wouldn't you know it, I got overly excited when I fixed a few pots and know I hear other problems.

First off, the Sansui is putting out more power and more open stage in the right channel, or maybe it's just more open stage.

Also I hear distortion from the left speaker, so I need to do further testing to see if it's the speaker and or amp. I know the distortion isn't coming from the Sansui.

Can someone that knows a Sansui AU-717 give me a few pointers on what to fix?
From what I saw when I opened the Sansui, the only thing that has been changed is the power cord.

Thanks.

 

[Sriskie]

It seems to me that the right channel is always a little bit stronger than the left, something about a stereo signal. I remember back when I used to record cassettes for my car the right meter always read slightly higher.

AU-717s are somewhat ticking time bombs. If you do some reading around here you'll find there are some things like corrosive glue, VD1212 double diodes and fuse resistors that need to be sorted out. I've done two of them and they're fairly easy to work on.

I don't know how much discrepancy you're hearing but you could try reversing the input cables and see what that does...

 

[preston1000]

Tried reversing the cables and the problem switched to the other channel. So I took apart the Sansui again and used Deoxit wherever it's needed. After putting the Sansui back together, same problems still existed.
I had ordered another pair of longer Beldens for a different placement of the amp and thought I'll plug them in and remove the shorter Beldens. Anxious to solve the problems, I wanted to see if the problems were coming from the amp and or the speakers. Put in a CD, turned it on and by the powers of audiophiles, the problems were no more and finally, equal soundstage and volume from both speakers. The only conclusion I could come up with about the Beldens is a bad solder joint.

I'm sure glad that's over with.