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NAD - Weak speaker channel when in phono stage mode after power on

P

P. S.

Active Member
Hi,
Maybe somebody has seen this problem with NAD 7220PE (or other) and can help me.

When I use my turntable with this amplifier - left speaker is less powerful right after I turn the amp on. I need to turn balance knob by 1/4 to center the sound. What's even more interesting - after 30min or so - the balance returns to normal and both speakers have the same level of volume. Also - it happens only in stereo mode (mono is just fine).

I narrowed the problem to be located somewhere in the phono stage. Here's what I did
- CD/AUX play just fine at all times
- confirmed with 2 different pairs of speakers
- replaced speaker cables
- used a different receiver (all good)
- swapped right/left RCA plugs in the turntable (no matter what - sound is always weaker in left speaker).
- cleaned pots twice! Paid special attention to input selector, volume balance

I've been looking for similar symptoms but cannot find anything. Don't know much about construction of phono stages to be able to diagnose problem myself. Maybe somebody can help?

Thanks!
-Peter
 
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Sounds like a job for freeze spray. There are 4 transistors and 6 electrolytic caps in the left RIAA preamp. After the unit has warmed up and is working properly, use the freeze spray to cool these parts in the pre-amp and see if you can force it back into the low output mode.
 
Step 1 is probably to confirm all solder joints are OK. My 7155 was intermittently dropping FM reception because of a loose solder joint that dropped when it heated up!
 
Thank you all for the inputs!
I already did resolder the RCA sockets to the phono board and it did not change anything.

Guess next steps will be to:
- examine the joints and check conductivity (not sure how to do it but seems logical to measure current between the leg of the board component and the solder joint. If I get readings - all good. If not - bad solder.)
- follow instructions from @Ylli and do freezing test. Here I assume I would either hear a drop in the channel or some distortion from the bad transistor (?)

I will keep you posted on my progress. I am actually both frustrated and excited at the same time to solve this puzzle - always good to keep your brain busy while listening to some good vinyl. ;-)
 
Yes, try to drip the freeze spray on one component at a time and listen for a change in level and/or distortion. BTW, some canned air can be used as a cooling spray if you hold the can upside down.
 
Considering my level of knowledge of circuits - I would call myself a "Jesse Pinkman of electronics" (if you watch Breaking Bad you know what I mean) but even with my limited skills I was able to follow the advice given in this thread and narrow down my problem to a faulty cap marked as C209 on the phono board!

It was quite a fun learning experience so maybe I share a bit of what I did ;-)

- checked for bad solder joints in the PCB. Used the "tin foil" method described here (https://www.jameco.com/Jameco/workshop/techtip/good-solder-connection.html) - turned out quite handy and showed all my joints are fine

- then I turned the amp on and tapped lightly on all the components in the weak channel path. Once I did it on the C209 - I heard a hum coming out of my test speaker. Hum was especially loud when I pressed my finger against the top of the cap.
- I sprayed the C209 with a can of air upside down so that it produces freezing air - the sound in the speaker has gone down immediately
- then I took my wife's hairdryer and heated the capacitor up - sound went to full blast in a matter of seconds

I tried to resolder C209 to make sure connections to PCB are fine but it did not help. I ended up ordering replacement caps and will replace them on both channels. Hopefully it solves my problem.

I really appreciate the help and advice given in this thread!
;-)
-Peter
 
To end the story - I ordered 4 Elna Silmic replacement caps. Ended up replacing all 4 such caps on the phono board just to be on the safe side from having another cap failed. That resolved all my problems and the phono stage works awesome!
 
Good fix. Enjoy the 7220PE. BTW if i haven't said it. Welcome to AK. When they sound good they sound GOOD. Have a 3140.
 
@Electone might consider that but I keep reading different stories of how full recapping changed the overall signature sound - sometimes it is for better sometimes for worse.

So far for all my gear I decided to take the approach "if it works good enough - don't fix it". ;-)
 
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