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Yamaha C4 control noise is making me crazy(er)

OldSubSailor

OldSubSailor

Member
About a year ago after years of saying "some day" I went all through my Yamaha C4 preamp replacing tons of caps. When it's working cleanly I've fallen in love with it again.... BUT there is one thing I couldn't effectively address that keeps popping up, especially if I've not used it recently, and that's some noise and the occasional dead spot in some of the controls like the 'sealed' volume control sections. Working them back & forth vigorously sort of cleans them up for a while (usually) but it is temporary and I cannot figure out how to get some De-Oxit into it w/o risking destroying an impossible to replace component.

Has anyone ever tried drilling a small hole in, say, a corner or the section covers to get some De-Oxit in them? I'm tempted but without knowing how they're laid out internally, very, very hesitant.

Barring that, can anyone offer a suggestion for a fix ?

Thanks in advance.
 
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Really don't like the idea of drilling holes in those sealed units.
Adjusting the volume adjusts the audio signal that the downstream electronics sees, maybe there is a problem downstream
though sounds unlikely from what you describe. With amp powered off I would measure the resistance on the volume pot
ie, for problematic channel between wiper and input, slowly increase the volume checking for smooth increase in resistance.
 
OldSubSailor said:
About a year ago after years of saying "some day" I went all through my Yamaha C4 preamp replacing tons of caps. When it's working cleanly I've fallen in love with it again.... BUT there is one thing I couldn't effectively address that keeps popping up, especially if I've not used it recently, and that's some noise and the occasional dead spot in some of the controls like the 'sealed' volume control sections. Working them back & forth vigorously sort of cleans them up for a while (usually) but it is temporary and I cannot figure out how to get some De-Oxit into it w/o risking destroying an impossible to replace component.

Has anyone ever tried drilling a small hole in, say, a corner or the section covers to get some De-Oxit in them? I'm tempted but without knowing how they're laid out internally, very, very hesitant.

Barring that, can anyone offer a suggestion for a fix ?

Thanks in advance.
Click to expand...
I would remove the volume control from the board. There are two nuts on the rear of the control. Remove the nuts and slide the long screws out of the control.Now you can carefully pry the segments apart just enough to get the Deox-it spray nozzle into the control to get the deoxit where it will do the most good.
 
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avionic said:
I would remove the volume control from the board. There are two nuts on the rear of the control. Remove the nuts and slide the long screws out of the control.Now you can carefully pry the segments apart just enough to get the Deox-it spray nozzle into the control to get the deoxit where it will do the most good.
Click to expand...

I do have a good vacuum desoldring station, but I may do that if no one else has some insight. If you've done that, do you recall if there's just an open area between the inside of the corners and the part of the control that the wiper slides along?

BTW, responding to one earlier reply, Unfortunately I and CERTAIN the problem is in the controls and not elsewhere in the circuitry.
 
OldSubSailor said:
I do have a good vacuum desoldring station, but I may do that if no one else has some insight. If you've done that, do you recall if there's just an open area between the inside of the corners and the part of the control that the wiper slides along?

BTW, responding to one earlier reply, Unfortunately I and CERTAIN the problem is in the controls and not elsewhere in the circuitry.
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The carbon resistor is bonded to a fragile ceramic disk.Drill bits are not forgiving to the ceramic pieces.Plastic swarf can FOD out the wiper brush.
 
avionic said:
The carbon resistor is bonded to a fragile ceramic disk.Drill bits are not forgiving to the ceramic pieces.Plastic swarf can FOD out the wiper brush.
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Ouch ... that sounds like a disaster waiting to happen.... I'm glad to know that even if it does reduce my options. I just wish I had a known good spare before attempting to pull it off of the PWB.

I wonder if anyone has ever tried / succeeded at replacing these with a suitable new ganged pot? Wiring it into the PWB could be ugly, but I could live with that if it worked smoothly when the case was back on covering up such a gerry-rig
 
I have probably serviced 20 or more C-4's in the past 8-10 years. Unsoldering the control is a piece of cake.
 
avionic said:
I have probably serviced 20 or more C-4's in the past 8-10 years. Unsoldering the control is a piece of cake.
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That's very encouraging. As I mentioned I have a good commercial grade desoldering station so the C4 just hit the next to the top position on my project list. I have a lot of other things going on for the next couple months, but I'll try to remember to come back here and report the results.

I anticipate that your answer will be "no", but still want to ask if there's ANY chance I could get some DeOxit into it where the leads exit the enclosures?

While I'm comfortable tackling just about any problem like this, 50+ years of hands-on electronics experience (I'm 68 and was both a tech and EE in my career) gives me an abundance of caution and a healthy respect for unintended consequences from having to clean up my own mess before I embraced an "... if it ain't broke don't fix it." attitude.

Thanks for the reply.
 
OldSubSailor said:
if there's ANY chance I could get some DeOxit into it where the leads exit the enclosures?
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Yes there is...See post # 3..
avionic said:
I would remove the volume control from the board. There are two nuts on the rear of the control. Remove the nuts and slide the long screws out of the control.Now you can carefully pry the segments apart just enough to get the Deox-it spray nozzle into the control to get the deoxit where it will do the most good.
Click to expand...

20 year Eagle "backshop" Avionic/ EW tech.
 
avionic said:
Yes there is...See post # 3..


20 year Eagle "backshop" Avionic/ EW tech.
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Yes, I saw that and what I meant (but didn't explain well) was to ask if there's any clearance around the pins coming out of the bottom of the control where I could get some DeOxit into the control. I'll pull them and look and, if not, remove the nuts as you describe to get access to the wipers.

Thanks again for the replies.

BTW I see you were Air Force. After growing up around vacuum tube technology (my father was an FCC licensed radio engineer and HAM), I spent 6 years in the Navy as a tech, then put myself through school to get an EE. But I was always a hands-on type of designer working in the lab with the prototype techs.

I was a long time president of the Iowa Antique Radio club and still tinkering with tubes and tube design some.
 
OldSubSailor said:
Yes, I saw that and what I meant (but didn't explain well) was to ask if there's any clearance around the pins coming out of the bottom of the control where I could get some DeOxit into the control. I'll pull them and look and, if not, remove the nuts as you describe to get access to the wipers.

Thanks again for the replies.

BTW I see you were Air Force. After growing up around vacuum tube technology (my father was an FCC licensed radio engineer and HAM), I spent 6 years in the Navy as a tech, then put myself through school to get an EE. But I was always a hands-on type of designer working in the lab with the prototype techs.

I was a long time president of the Iowa Antique Radio club and still tinkering with tubes and tube design some.
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Are you here in Iowa? Thanks for your service.
OldSubSailor said:
BTW I see you were Air Force. After growing up around vacuum tube technology (my father was an FCC licensed radio engineer and HAM),
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That sounds very familiar. My father was a field radio operator/technician instructor Army at Fort Gordon during Korean war. Serviced Business band,CB,SSB and HAM radio locally and is FCC licensed as well. KAOCSI
 
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I was trouble shooting and repairing CB,SSB and linear amplifiers before I had my first formal basic electronics class.:biggrin: Dad was and excellent instructor.:naughty:
 
OldSubSailor said:
was to ask if there's any clearance around the pins coming out of the bottom of the control where I could get some DeOxit into the control.
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Only if you disassemble it.Otherwise, no, there is no openings.
 
Blue Shadow said:
I sense someone needs to see if they can arrange an audio get together.
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Maybe at some point..... my life is WAY too busy right now as I'm helping my wife recover from a near fatal car accident. It's a long story I'd rather not get into, but suffice it to say that we've got one or more appointments on the calendar EVERY day this month except Christmas day.
 
OldSubSailor said:
Maybe at some point..... my life is WAY too busy right now as I'm helping my wife recover from a near fatal car accident. It's a long story I'd rather not get into, but suffice it to say that we've got one or more appointments on the calendar EVERY day this month except Christmas day.
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Sorry to hear about your wife’s accident. Hoping for the best recovery outcome possible.

FYI, I host an audio gathering not too far from you every fall. If you like, I’ll add you to the list to notify when it’s time. I believe we’ve actually met in real life a while back. I used to live in the Timber Creek area and believe we have a common interest in Volvos. Am I thinking correctly?

Best wishes to you and your wife.
 
Leben said:
Sorry to hear about your wife’s accident. Hoping for the best recovery outcome possible.

FYI, I host an audio gathering not too far from you every fall. If you like, I’ll add you to the list to notify when it’s time. I believe we’ve actually met in real life a while back. I used to live in the Timber Creek area and believe we have a common interest in Volvos. Am I thinking correctly?

Best wishes to you and your wife.
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Yes, that would be me.... where did you live around here?
 
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