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Marantz 2270 noise

tkrilly

tkrilly

New Member
I got myself a 2270 in pretty decent shape a couple of weeks ago, dead quiet at full volume when no input signal present, with only a couple of burnt bulbs. Unfortunately I couldn't resist the urge and went into fixing the lights, then continued by replacing all the electrolytic caps on the P800 board (C801-C807, C810 with Nichicon type), followed by the replacement of the two big caps and a relay for a good measure. Alas, after I powered it up again I noticed a substantial noise/hum that changed if I touched the chassis, which made me believe I was dealing with some sort of a ground loop issue. The noise was most pronounced on the phono input. I tapped all the replaced components to see if there was a poor solder job done somewhere to no avail. I uploaded the video where I switch between phono and aux inputs here:


The noise and its changes can be clearly heard. Prior to that, I adjusted the R809 to set the voltage level to 35V, and measured the noise on it, which was on 10mV level (please see the attached scope pics here https://drive.google.com/drive/folders/1EpgpkBAqkr4Utj02Q2rcMPBGbNJ-eZWp?usp=sharing ). Then I a checked the voltages on BCE of the following transistors (SM reference values given in brackets):

H803 B 13.8 (14.2) C 30.5 (32.6) E 13.2 (13.5)
H805 B 35.6 (35.7) C 44.2 (44.0) E 35.0 (35.0)
H806 B 7.8 (7.8) C 35.6 (35.7) E 7.2 (7.1)
H808 B 0.0015 (0.0) C 0.9 (1.25) E 0.0 (0.0)
H809 B 1.25 (1.25) C 1.0 (0.8) E 0.7 (0.7)
H810 B 0.7 (0.7) C 1.0 (0.8) E 0.0 (0.0)

As far as I can tell none of the values are too far off, except maybe for H803B. At this point I am lost on how to proceed and would really appreciate the suggestions and expert opinions of other AK members who have done such troubleshootings in the past.
Eternally grateful,
Jurij (Yuri)
 
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It looks right. Just be sure all of those grounds on the center bar have good, well flowed solder joints. Hum in Phono mode on these Marantz receivers is normal if the bottom is off. If it is, try putting it back on and see what happens to the hum. If still there, it sure sounds like a grounding issue somewhere.
 
I heard similar hum noise when I tried to fix Maranrz 2275. But after I put all the covers on, especially the bottom cover, the noise disappeared. It also disappeared when I lifted the receiver and landed on the side even without the bottom cover on. But this is 2275, not 2270.
 
Thank you both, I tried side position, and bottom cover on. Side or normal position makes no difference (bottom cover on or not), with bottom cover on, the hum and buzzing is still there but it doesn't react to tapping or touching the chassis anymore. I will try re-flowing the solder on the ground lug for the big caps and see if it makes any difference.
 
I melted the solder on the lug and added some more of it but the outcome was the same, no change in the noise level.
 
I tried flipping the plug and although the noise was somewhat different (in frequency spectrum) , the level stayed about the same in both orientations. I checked the DC offset, which was couple of mV and bias current. On one channel the voltage was constantly creeping up for ~30min but then remained constant, on the other, it was slowly (in the matter of minutes) oscillating from 5mV to 25mV. I adjusted both to 10mV although I couldn't be sure where it went on oscillating channel after I connected the speakers and checked for noise, it didn't change a thing.
 
It was quiet before you started, and had a hum after working on lights, power supply and big filter caps. To state the obvious, it’s going to take close examination of those areas. Check polarity of everything you changed on the power supply. Look for a good ground from power supply to chassis. Look for cold solder joints or solder bridges on the bottom of the board. Reflow anything that looks suspicious. Screws tight on the power supply board? Look at the wiring around the lights. Anything out of place? Pinched wires? Filter caps look OK if your soldering is all good. Make sure the drop-down leg on the ground bar of the big caps is securely fastened to the chassis.
 
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Steven, thanks for the suggestions, my paying job has kept me from what's really important this past week, and so far I've only managed to check the power supply board and the lights. All the caps are the correct value and polarity orientation, no solder bridges or cold solder joints, anything looking remotely suspicious was soldered again. Same with lights, pulled them out one by one and checked again for twisted wires, unwanted connections, bridges or cold joints. The only weird thing I noticed was that one of the 6.3V/40mA bulbs had different resistance than others. For majority it was ~19 +/- 1 ohm, the weird one had almost double the value. Nevertheless with or without that bulb in place, the hum and occasional crackle was still there. Moving onto relay (will put the old one back in and check) and big caps. Hopefully I find something there.
 
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