Marantz 2252b hum right channel, distortions left channel

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Daochuoi

New Member
Good afternoon,

I recently acquired a 2252b, upon connect to set of speaker using aux as input, even when the volume at 0, there a hum sound from the right channel. Slowly turning the volume up and I can hear static and distortion from the left channel. So I gave the pots and switches with deoxit treatment, and work them switches and knobs many times. The next day I connect it to speakers again but the problem still persists.
Next I used a separate power amp and connect it to the pre out and run the speaker from the power amp, everything sound fine on both channels! Tried all the button and it seem to work fine, no scratchy noise or hum or distorted, all this work fine on aux and fm input. I still have problems when speakers connect to the receiver, no matter which input I select. Tried the “main in” input and use my phone as a source, also having same problem. Plug my headphone into the sterephone jack and I can hear that hum from the right channel, but the left channel sound fine.
I am a newbie at this, wonder if there anything I can try to look into, beside send it to the tech, as I do not have experience with troubleshooting, been google and search the forum, as I am also wanted to learn

thanks,
 
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Hi and welcome. The connection between the Pre-amp output and Main In on the 2252B is with contacts within the RCA jacks of the Main In. Sometimes these become oxidized. Have you tried to connect the Pre out to Main In using a short stereo RCA cable to see if it improves. You might also be able to clean the contacts with contact cleaner spray or isopropyl alcohol on a cotton swab. Just be careful that the cotton tip does not come off inside the connector. Do you hear only hum on the Right Channel, or music + hum as you turn up the volume? Can you better describe the "static" and "distortion" you hear on the Left. Is it a crackling or overdriven sound?

CAUTION: When poking around inside the receiver with the covers off, there are voltages present on the capacitors even when unplugged from the AC.
Be CAREFUL or you will get a shock. You will need to discharge the main filter capacitors before probing. Do you have any test equipment and can you read a schematic?
 
dankik said:
Hi and welcome. The connection between the Pre-amp output and Main In on the 2252B is with contacts within the RCA jacks of the Main In. Sometimes these become oxidized. Have you tried to connect the Pre out to Main In using a short stereo RCA cable to see if it improves. You might also be able to clean the contacts with contact cleaner spray or isopropyl alcohol on a cotton swab. Just be careful that the cotton tip does not come off inside the connector. Do you hear only hum on the Right Channel, or music + hum as you turn up the volume? Can you better describe the "static" and "distortion" you hear on the Left. Is it a crackling or overdriven sound?

CAUTION: When poking around inside the receiver with the covers off, there are voltages present on the capacitors even when unplugged from the AC.
Be CAREFUL or you will get a shock. You will need to discharge the main filter capacitors before probing. Do you have any test equipment and can you read a schematic?
Click to expand...

hello!
Yes I did connect the main in with the pre out but the result is still the same. The only testing equipment I have is the digital multi-meter, and I have some knowledge going through the schematic.
I uploaded a video to YouTube showing the receiver operating, please excuse the background :) I was using my daughter iPad to record and my phone as a source connect through aux. at the beginning I was trying to move the ipad closed to the speaker as possible so you can heard the noise on the right channel, while left channel is quiet. I tried the balance left and right to capture the left channel muffle sound
 
This is probably obvious, but did you try switching L & R speakers (and wires) to the receiver to make sure the problem is not with the speaker?
 
Update
Check the voltage between R764 & R766 - climbing up to 70mv, so I adjust it down close to 24mv.
- adjust J718 & J714 - close to 0 mv as possible
- adjust J717 & J714 - close to 0
When checking between R763 & R765 - I can not get any reading no matter how R731 ajdust

power supply check between J722 & J728 - 35.73 V
 
Daochuoi said:
When checking between R763 & R765 - I can not get any reading no matter how R731 ajdust
Click to expand...
Did you connect the DMM leads here?
Also, from the SM "When adjusting a DC offset voltage, the switch of the SPEAKER SYSTEM-1 must be turned-on." Did you check this?
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Last edited:
Yes
https://ibb.co/hLQDnMY
https://ibb.co/kcxVByX


kcxVByX

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dankik said:
Did you connect the DMM leads here?
Also, from the SM "When adjusting a DC offset voltage, the switch of the SPEAKER SYSTEM-1 must be turned-on." Did you check this?
View attachment 2873336
Click to expand...
I just finished repairing a 2252B with the same left channel issue. The bias on the left channel was non-existent, no matter what I tried, always staying around 0.1 to 1.0mv.
After taking the thing apart several times and testing transistors I gave up and started checking all the resistors for drifting!! What I finally found was that R725, right behind the left channel Bias pot, was reading 50% higher than spec'd......replaced and problem was cured!!

Just an FYI!!
 
One thing I do when setting up to do bias adjustments is to (power still off), measure the resistance to be sure I'm connected. It should be the value of what it's across and in this unit it's two resistors so should be twice the value. Keep in mind that small meters like this will not read absolute zero and you can get your base offset for low ohms readings by touching the probes together. Say that reads 0.2, then a reading across a 0.5 ohm resistor would read 0.7 so must be taken into account.
 
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