• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Maran 4400 scope distorted

R

Roosch

Member
Hello dear marantz-enthusiasts. Alas, my dear 4400 beast stopped playing its wondrous tunes yesterday... :(
I have had repairs done on it before and some months ago I fixed a distorted sound on one channel after finding that one of the output trannies was loose !
But yesterday I found that all its channels were dead even phones jack. Connecting my kenwood kr 10000 through jumpers to marantz I found that the marantz preamp still worked.
After inspection I found that the top 1s2724 rectifiers before filter caps was dead.

From reading an interesting suggestion in a post by Echowars;
http://audiokarma.org/forums/index.php?threads/marantz-4400-quad-repair.42452/
, I took out the two diodes and replaced them with a 35A 4 terminal bridge... and .... it worked!! :banana:

All channels are back online and the receiver once again sound great....
However, a new issue has emerged and I'm at a loss.
The scope that previously worked, now has an issue I don't understand. Instead of being focused as a dot, it makes a somewhat circular curve on the screen when music is off. In stereo mode it still moves somewhat correctly but in varimatrix it clearly does not.
Strangely also when disconnecting the big wire plug to scope assembly board, this scope curve is still there even when scope button is turned off.
My 2sk30 trannies that I've replaced a few years ago seem okey. Could there be current leaking into the scope from somewhere...causing a curve instead of dot?

If anyone can give me any pointers as to what might be the problem or have any ideas about this issue I would be very thankful.:beerchug:
I guess the issue could have arisen as a result of swapping the diodes for a bridge... otherwise maybe something took a blow when the rectifier stopped working but I didn't see any smoke etc.

Well, if anyone comes up with anything It would be much appreciated. I really want to keep this beast with a functional scope :beatnik:

Mm and one more thing, are the ceramic small caps that were wired before the filter cap rectifiers still mandatory to have when using a 35A bridge? I have tried both ways and it seems to work either way...
 
Last edited:
Register to hide this ad
The ceramic capacitors on the rectifier are to squelch 'switching' noise as the rectifiers turn on and off. You may hear it on the Marantz or a nearby radio on the AM band.

Good luck with your scope problem, be careful of the high voltage.
Tom
 
Thanks Tom, I will resolder the ceramics to the bridge to minimizer risk of that issue.
Yeah scope will be further investigated, I might look into power supply board to see if any issues have arisen... although I completely refurbished it a few months ago and it worked terrific.


catrafter said:
The ceramic capacitors on the rectifier are to squelch 'switching' noise as the rectifiers turn on and off. You may hear it on the Marantz or a nearby radio on the AM band.

Good luck with your scope problem, be careful of the high voltage.
Tom
Click to expand...
 
catrafter said:
The ceramic capacitors on the rectifier are to squelch 'switching' noise as the rectifiers turn on and off. You may hear it on the Marantz or a nearby radio on the AM band.

Good luck with your scope problem, be careful of the high voltage.
Tom
Click to expand...

Alright, ouff I have worked for many hours now trying to find the culprit of this scope issue.
First of all I resoldered the ceramics to the newly installed 4-terminal bridge. No effect on the scope issue however.

I have investigated the pre-amp, varimatrix, power supply, diode matrix assembly and scope assembly boards for faulty transistors or diodes. Nothing. There are some tantulum caps i havent checked yet though...

Still the scope is displaying a somewhat circular curve with no signal to it, instead of the classic Dot I had before one of the big filter cap rectifiers died.

Could it be that the curve scope issue arose as a result of installing the 4 terminal bridge instead of dual rectifiers? I feel it more probable that something took damage when the rectifier died, since everything else works fine.

Does anyone know what could cause the Classic dot to turn into a curve when no audio signal is applied? When audio signal is there, it moves almost normally in stereo setting. In varimatrix, however the curve moves but not properly in 4 directions. I had an issue with the diode matrix assembly a few years back, where swapping the 2sk30a trannies got the scope working again. My problem back then was that in varimatrix mode (mainly) the scope didnt move in all 4 directions. But could a problem with these trannies also give rise to a curve instead of Dot?
I was wondering if maybe ground voltage could be leaking into scope circuitry and cause this curve? If anyone has any clues, it would be much appreciated. Has anyone ever encountered this curve instead of Dot issue?

I have ordered new 2sk30's and will be replacing them on both scope board and diode matrix board, since I am now fumbling in the dark

All the best marantz and especially scope fans : D
 
You must log in or register to reply here.
Back
Top Bottom