4230 repair question

jasong

Music enthusiast
Hi again: a while back I posted a thread about a 4230 repair project that I have on the go.

Here's another crack at an answer to the basic question:

The unit seemed to sound OK upon turning on, but when turned to higher volume (12:00), started distorting and making a "nanananananana" oscillating sound.

Do any gurus have any insight as to a basic cause of this? I posted schematics and whatnot in the original thread.

Some insight would be much appreciated...Helmut...gigapod...EchoWars...anyone?

Bueller?
 
Sounds like a bad amplifier stage. Could also be the pre amp section. You'll need an oscilloscope to track down the source of distortion.
BTW. Does it 'distort' in all modes or just in phono?

Ron
 
Sounds like a bad amplifier stage. Could also be the pre amp section. You'll need an oscilloscope to track down the source of distortion.
BTW. Does it 'distort' in all modes or just in phono?

Ron

In all modes. By the way, only in the right channel. It had been recapped before I got to it too. Thinking about it lately, I was going to replace the transistors in the main amp board. I'm pretty sure the problem is in the right board for the main amp...so now the question is which transistors to use?
 
Just replacing parts is not the answer. You must verify the section that is causing the problem. Does it have pre-main jumpers? if so drive the amp channels seperately from the pream does it still occur?
 
Try the pre-out main-in function to help isolate the pre and power amp sections. Don't replace parts without first determining that it/they are the issue.

Ron
 
Try the pre-out main-in function to help isolate the pre and power amp sections. Don't replace parts without first determining that it/they are the issue.

Ron

Yeah I already did that. I have had it opened up and sidelined for a while, but I did do the pre out main in test as you describe, and it worked fine when using another amp as the main. This is what led me to the right main amp board. The problem is, as far as I can tell, localized in the right main amp board. (Incidentally, this board had been recapped with higher voltage Rubycon caps at some point in the past, and even they had started to bulge).

It may be a lost cause for all I know...but it would be great if I could fix it. It seems that a recap may be ineffective, unless as the service manual suggests, one of the very low value ceramic caps is causing parasitic oscillation. I don't, however, know what parasitic oscillation sounds like.
 
It's not so much what it sounds like rather what it looks like on an oscilloscope.
You really need to pull all boards and compare components to what's listed in the service manual. I wouldn't power up the amp until you check the parts in the amp to the parts list. You can compare the left and right amps as well since the left side works.

Ron
 
It's not so much what it sounds like rather what it looks like on an oscilloscope.
You really need to pull all boards and compare components to what's listed in the service manual. I wouldn't power up the amp until you check the parts in the amp to the parts list. You can compare the left and right amps as well since the left side works.

Ron

Oh but if I only had a scope. *sigh*

The parts are all original and matching on each side save for the replaced caps as mentioned.

What I will do, and what's probably the best, is replace the obviously bad caps and power up again, then scope it at various places. Which will take a while...although I have a hunch it's the transistors. Would also like an ESR meter too...
 
If you don't have a scope then take a punt and replace all the caps in that circuit sounds to me like its a good place to start looking.
The voltage rating on caps isn't important as you can replace a 16v cap with same value but in 20v cap. (Value IS important!!!!!!) Oh and don't put the electrolytic caps around the wrong way!
Its not a lost cause! Gee even if you went as far as replacing every transistor as well it wouldn't cost you that much. Keep at it at least you know what board its on!

cheers and good luck.
 
Thanks for the encouragement dude. :) That was pretty much the plan. See, buddy doesn't even want the amp anymore; this is a salvage more than anything.
 
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