Deoxit job gone awry?

D

Deegan

New Member
Hello,

Just did my first deoxit job on a Sherwood 7100-A. I was having issues with the left channel cutting out.

I followed the idiots guide posted on here on the site. Pretty easy process - so it seems. I was careful about taking it apart and putting it together. I used D5 and then the gold stuff. I let it dry for a few hours and then fired it up. It worked great last night. I played a couple albums and it sounded great - both channels clear and warm although the left was still a bit quieter than the right.

And now, today, I turn it on and I'm getting loud feedback hum out of the left channel. Happens with speakers A and B, with Phono and FM - so I assume it's the channel.

Any ideas what happened? Did I cross something on the inside or short something?

Any help greatly appreciated!

Thanks!

Chris.
 
If the pot's element is conductive plastic or carbon, then yes it could be ruined. Otherwise, could be just a loose wire, internal connector dirt, or a solder joint that got knocked loose.

Also, the "Gold" product is safe for plastics, but is meant for gold, silver, rhodium, copper, bronze & nickel contacts. I have never heard of anyone using it for pots, but I guess mileage may vary.
 
well, that sucks.

Is it a question of cleaning out whatever coating element the Gold spray deposited in the Pots with D5 and then faderlube? Or is more like I killed it.
 
Try them both again maybe conserving the D5 and wasting the gold and feel free to minimize drying time by half.
 
Try flushing them out with a non-residue, plastic safe electronics cleaner like CRC QD electronics cleaner, available at a lot of auto parts stores. Let them dry out and try them before adding any Faderlube. If that gets them quiet, then apply Faderlube.
 
I want to thank everyone that's posted on this thread. A lot of good information that will be put to use by many. This is what makes the internet worth it!!! and porn too don't forget porn!!!! snort... AND it might be a re-post but it puts all of the previous thoughts all in one small footprint!
 
Sometimes the headphone jack can also get dirty. Place a pair into the unit and listen and see it the channels are equal.

You did do all the switches, tape monitor, stereo mono? Did you spray fader lube into the controls? Fader lube is for sliders.



Barney
 
revisiting.. playing records? ground wire connected to from TT to amp? Same condition on all inputs?
 
Thanks for all of the responses!

Yes, playing records and the ground is connected. Same problem with Aux, FM and Phono on both A & B speakers.

One interesting thing (to me, an electronics novice) is that the hum seems to be at full strength regardless of volume. So even with the volume all the way down the feedback noise from the speaker is at full strength - and when I use both A&B speakers together is is reduced by roughly half (which makes sense to me).

I think Binkman is probably right and the left channel was on it's way out before I pushed it over the edge. I will try going over it again and look for loose connections, etc. I guess I should be thankful I didn't learn on something more rare/valuable.

Thanks again. Great forum here.
C
 
IMO your pot is shot.. likely it was iffy before the DeOxit ruined what was left of it.
(I refuse to use that stuff on Anything... but that's just Me :)
IMO Fit a fresh pot.
Even a V cheap ALPS Clone for ~12$ from Ebay will be a whole new world better than a 40 yr old carbon pot.
 
De Oxit ?

What do you use instead, I was about to try my hand on my KLH 54, its pops and has static when almost any control is moved, so I assume it needs some sort of cleaning.

????

bare said:
IMO your pot is shot.. likely it was iffy before the DeOxit ruined what was left of it.
(I refuse to use that stuff on Anything... but that's just Me :)
IMO Fit a fresh pot.
Even a V cheap ALPS Clone for ~12$ from Ebay will be a whole new world better than a 40 yr old carbon pot.
Click to expand...
 
There are some sherwood pots on the volume that are sensitive to cleaners and the wipers get hit being plastic glued on etc. but the other pots should be okay.. Other condition was the deoxit would kill the vol. pot switch combo located and mounted in the rear. Lill plastic lever would rot out.

Might find a replacement for the pot.. I think it's a classA and gain off the volume pot? Getting a dual pot is the problem. Amps don't have to be 'pretty' so modification is always an option.
 
Loud hum. Check all of the RCA connections and interconnects.Usually dirty controls don't create loud hums but do cause drop outs ,crackles and static when they are moved. Loud hums can also be created by broken ground connections within the unit.
 
Last edited:
Hey thanks Avionic!! Feedback.. been nagging me on and off for hours. Makes a lot of sense.
 
Why is this called "feedback" hum? Is hum downstream being selectively fed back and regeneratively amplified? I think the suggestion is that the path is just picking up "ambient" hum because of faulty shielding / grounding.
 
I took it apart again and checked all of the connections. Can't seem to find anything awry - but honestly I don't really know what I am looking for. No broken connections or obviously bad components. I followed the ground wires inside the unit and they all seem to be intact. The RCA connections are all intact.

The right channel is still working fine. Binkman, has the 'feedback' comment changed your mind about the left channel being kaput? Or is that a potential symptom of a bad channel. Replacing a channel is beyond me - but maybe fixing a feedback issue isn't?

Thanks again for the comments.
 
Right now. All your getting is a loud hum on one channel. Feedback ? Can't tell from here. Probably going to need a tech to check it out.
Now , a broken sheild/ground on your interconnect cable(s).Can produce a loud hum. If its in the selected signal path.


Another cause of a loud hum could be a bad electrolytic cap within said amplifier circuit.
 
Last edited:
avionic said:
Right now. All your getting is a loud hum on one channel. Feedback ? Can't tell from here. Probably going to need a tech to check it out.
Now , a broken sheild/ground on your interconnect cable(s).Can produce a loud hum. If its in the selected signal path.


Another cause of a loud hum could be a bad electrolytic cap within said amplifier circuit.
Click to expand...

This "feedback" thing I still don't understand. Are you referring to true feedback like you have in an oscillator or when a speaker vibrates a microphone, or guitar strings? Is this 60 Hz (or 120 Hz) being tapped from somewhere downstream in the audio chain and fed back upstream for recursive amplification? I've seen speakers oscillate at around 2 Hz but I think the only oscillation going on with the hum happens back at the power plant.
 
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