Working on C-65

[Soundscape]

I've seen the sealed internal grease turn to gelatin over time on other pieces. Heck, it's 40 years old. I want to believe I can soften it again...while treading the line of leaving well enough alone. I shot my C-80 gelatin pot with some D5 sauce and seems ok 5 years later. Ugh.

Him haw Jones

 

[Nashou66]

I'm servicing this piece now, and wondered what ya'll do with a nice functional volume/variable loudness pot on these? Do ya leave it alone? It's a non servicable ALPs pot. I don't intend to service it from reading prior threads on it.
But, though it's sealed, greased, and somewhat safe from dirt. Why did they provide side holes?
I wanna squirt my D5 straw right in there but don't wanna F things up. What would you do? Spray away?
Thanks
View attachment 3743838

Do you remember this thread?

Thread 'C-70 Volume intricacies …'

Aug 6, 2024

I am posting this hoping it’ll help someone down the road.

A while ago I acquired a C-70 in decent shape that needed cleaning more than anything. After cleaning came testing when right away there were problems with intermittent audio and also the Rch (or Lch, can’t remember) was completely missing. I traced the problem to the volume where incidentally noticed an ever so slight wobble in the volume shaft as well. Since this is a Japanese version of C-70, there are stark differences when compared to the US model. For example, the volume is a 24KΩ special taper Alps volume (RK21 series), as...

• Sparkplug
• Replies: 5
• Forum: Yamaha

• 

Nashou

 

[Soundscape]

My shaft ain't bent just wanna know it's safe to squirt D5 or D100 in the hole of a non service pot.

 

[Nashou66]

Id use Faderlube instead

 

[Soundscape]

Id use Faderlube instead

Yeah, I'll do that. Ooh I almost forgot...I have a big can of fader lube sitting around.

I read the D5 thread recently too; and it's cautionary carbon track notes. Fader lube it is then. Thanks

 

[nakmandan]

The only downside to spraying out pots is it removes the damping and protective grease inside. This can turn a nice smooth pot that has a good turning feel to it into a no mechanical resistance, too easy to turn pot that feels "cheap". There are a couple of ways to know if your pot needs cleaning or not. If the pot is a level control such as an input or output level pot, you can run a signal through it and observe the sine wave on a scope. As you rotate the control, the sine wave should remain smooth at all points in the range of the pot, and merely change amplitude, with no distortion at all. If the sine wave jumps around, goes blank at different points, or is noisy, then the pot definitely needs cleaning. The other way to check it is to take it out of circuit to isolate it and not get false readings. Attach it to a ohmmeter, either an analog with a needle or if digital, one with a bar graph display as well as the numeric digits (numeric digits alone are to hard to see smooth changes). First check the outer terminals to verify the pot is conducting through the whole track. And it should be usually within 10% of its stated value. Then change the leads to one end and the center terminal and rotate the shaft slowly through its entire range while observing the meter. Just like looking at a sine wave on a scope, there should be no jumping around readings, glitches, dropouts, or anything but smooth changes in resistance. If you have smooth changes with no noise through the entire range of the pot, you can probably leave the pot as is.

The other thing you can do if you have to spray the pot out is replace the grease. While Faderlube (Deoxit F5) has lubricant in it, it doesn't have the same feel as grease. There are dielectric greases available form many manufacturers. Caig makes several different greases for different situations. Even WD-40 brand professional line (not plain ol' WD-40!) make a product that is good for this purpose. Mr. Carlson's Lab did a video on this a few years ago, which I can't find at the moment. The WD-40 professional product is an expanding spray foam type of grease and is super messy, and requires a fair amount of cleanup, but it works well.

 

[Gdizard]

Is it possible to determine what a potentiometer values are if you need to find a replacement?

 

[avionic]

Is it possible to determine what a potentiometer values are if you need to find a replacement?

Yes. Read the schematic and/or the parts list( Yamaha part number) in the service manual. The potentiometers casing is also stamped with the (ALPS part number) as well as resistance value and taper code.

 

[Soundscape]

Are there any modern replacements for TR149 & TR150 on these? Heat sink mounted pass transistors in the glue area.
Honestly my old ones test OK at the moment and it's making music. But, I'm concerned about the longevity of them. Serious heat on these 2. They burnt my pinky!


Darlington Jones

Hfe- 41 on one
Hfe-140 on the other

 

[Nashou66]

Maybe these?

https://www.st.com/content/ccc/resource/technical/document/datasheet/6d/08/86/eb/dc/af/41/f5/CD00000917.pdf/files/CD00000917.pdf/jcr:content/translations/en.CD00000917.pdf

Nashou

 

[Soundscape]

Yes I do.
My SOP is replacing these with.
Toshiba TTC004B Q

https://www.mouser.com/ProductDetail/Toshiba/TTC004BQ?qs=Mv7BduZupUgP0%2FeZ2DvzIw%3D%3D

And TTA004B Q

https://www.mouser.com/ProductDetail/Toshiba/TTA004BQ?qs=Mv7BduZupUjGQix8c1RZeA%3D%3D

Same pin-out ECB..
These output transistors for MC phono pre-amp tend to run hot and These TO-126's will handle the heat.

Sidenote unrelated to post #29. Just FYI fellas Mouser is out of the TTA004's now...zero stock. Digikey has 110 left at the moment. Thanks for this great tip Sensei Avionic in the phono stage.

 

[avionic]

Sidenote unrelated to post #29. Just FYI fellas Mouser is out of the TTA004's now...zero stock. Digikey has 110 left at the moment. Thanks for this great tip Sensei Avionic in the phono stage.

I have already stocked up on them months ago. Next shipment to mouser is mid-July.