Marantz 4270 phono output: left channel weaker!

Dusko S.

New Member
Good evening, everyone!
Let me first say thanks for this forum, it was very helpful in my Hi-Fi endeavors so far, just from reading the informative post on here.
So here I am with a problem.
I recently bought an Marantz 4270 in an excellent state, allegedly serviced, and partially recapped. Not sure when (or if) the service took place.
All in all, the reciever works more or less flawlessly, I did clean the volume and tone controls, all the switches and sliders, a few were only a little in need of that (soft crackling when used).
All inputs and outputs sound great, no problems there.
Except off course, the phono...
Sound is clear and full on the right channel, and slightly weaker (and even muffled a tiny amount) on the left.
Not much, but well enough to notice it just from first listen. I did clean the input jacks. The problem goes away when i switch to mono.
I did use a cheap phono preamp i had lying around to test, and yes, on all the other inputs the turntable works fine. So, I´m guessing the problem could be somwhere in the phono stage of the reciever. (cap,transistor?)
Where to begin to look for the culprit? I would really want to get this solved, and not use an external phono preamp.
Thanks for any advice guys!
 
Hello, I've just acquired a 4270 myself and has a similar issue with the CD-4 / Aux input. Contact cleaner fixed my issue with the aux input. Perhaps another cleaning of the input selector? I'm not the expert but it might be interesting to know if you hear with headphones as well? The headphone signal is ahead of the speakers protection circuits, this might be a good data point for the experts.
 
Hi, Jxmos!
Good point, I forgot to mention it, thanks! Yes I have the same issue with the headphones on, left channel is just halfway there. I could and probably will do a one more once-over on the pots, and have another close look at the insides, although I did not find nothing suspicious to my (not expertly trained) eye. I hope I figure it out, I´ve been listening to the reciever last couple of days and absolutely enjoying it. Perfect in every aspect, except for this. Cheers!
 
Replace the electrolytic caps in the phono stage.
Thanks, Dr.
Yes, I thought that would be the next move to make, if someone here doesn`t have a magic trick up the sleeve for this situation. I hoped I wouldn`t have to apply my lacking skills on this beauty, but yes, I have already repaired an amp before and probably will end up changing that couple of caps to see where it goes from there. While on that subject, can you tell me or direct me to some good makes and values for these caps?
Thanks.
 
Nichicon UKL for low noise/leakage apps
UKA for signal path, UPW or other low ESR type for power supply filtering, match uF,V can be same or higher, diameter,lead spacings.
 
Good evening, guys!
Sorry to report - no luck!
I recapped the whole P 400 phono board, and everything is still the same. Weaker left side, full signal only in mono, on headphones and speakers...!
I changed all the electrolytics, all good quality caps, nothing bad there. Where to go from here? Everything else on the reciever is perfect.
Thanks for any suggestions!
 
If you haven't done a thorough Deoxit treatment of the input select switch, you might try that. That's one place external to P400 that could have an effect just on the phono section. It's a long shot, but worth trying.
 
What you really need now is an oscilloscope and an audio generator to trace the signal and find where it is getting lost.
 
If you haven't done a thorough Deoxit treatment of the input select switch, you might try that. That's one place external to P400 that could have an effect just on the phono section. It's a long shot, but worth trying.
I already did, twice. Not a Deoxit treatment per se, but a good contact cleaner, and it instantly cleared what little crackling there was. It was pretty clean to begin with.
Cheers!
 
What you really need now is an oscilloscope and an audio generator to trace the signal and find where it is getting lost.
Unfortunately, I don´t have access to neither at the time. Nor am I that familiar with the process. Not to say that I won´t soon learn. That would surely be the quickest way.
I would still bet something´s wrong on the phono board. What´s the next thing to go after the capacitors? Is there a usual suspect? I mean, this phono board is not that big or complicated, If theres something off, it would be easy to find/replace. By the way, I think this phono section sounds really nice, compared to my other amp`s (70´s Akai ) or a cheap phono preamp hooked up to Marantz´s aux.
 
When I set mono, my left channels are still weak, when I enable loudness they sound like they should. Someone took too much money, cleaned the pots an relay, replaced bulbs, two capacitors and some transistors that amplify the rear left, but additionally the rear left is still even quieter than right.
I have weak left channels on all Inputs, also tuner. It seems to be less there, but only on loudness war music and speech.
Can someone confirm having a weak channel repaired and how, not just a dead channel playing anything again?
 
There is a switch on the back for the remote which causes this problem try Deoxing it. That solved this problem with mine.
 
Back
Top Bottom