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HELP?? Noise while turning/adjusting ANY instruments volume.

Started by Theors, August 17, 2015, 12:25:25 AM

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Enzo

In the schematic:

I = input
G = ground
CA = who knows.

I think the schematic is drawn wrong.  I do not believe the CA point from the jacks is connected right to C+.  That would do nothing useful.  Look at the drawing on the right, where CA is now.  Transistor Y.  Why not trace where CA goes and see if maybe it goes to the base of Y instead of the collector.

Just looking, I'd predict the CA is some sort of mute, and plugging into either jack defeats it.

Theors

 :-\ Well......it's not the jack. Basically if I eliminate the Purple wire (CA) which I confirmed touches the Tip of the cord when cord is inserted and touches nothing when not,....the amp will work fine on a simpler two wire jack AND the original jack less the (CA) circuit. So the problem lies within that (CA) circuit? Correct? I tried to physically follow that circuit but got lost in the process to many times. (Seeing cross eyed now) :loco What next?... to keep the full features of the input jacks.
'82 Carvin DC200 + others

Theors

I'm going to try and describe what I see as the schematic of the input jacks:

When cord is inserted,
•Red(I) contacts Tip.
•Black(G) contacts 3 surfaces: 1-Sleeve 2-Ring 3-Becomes disengaged from Red(I) when cord is inserted.
•Purple(CA) contacts Tip also. (yes it's dedicated right to the tip)

Resistors:
68k inline with Red(I) Tip
22k inline with Purple(CA) Tip

Can anybody draw it? Is it different from what the schematic shows?

Also Enzo, I think I get what your saying about transistor Y. Isn't that the voltage amount that was showing up at the tip of my cord? Bad transistor?
'82 Carvin DC200 + others

Enzo

If the schematic even suggests the real circuit, the I and CA do not connect directly to the jack, they connect through resistors.   I is what should connect to the two tip contacts, but through 68k resistors.  Those two rsistors cross connected through the two jacks is the same as the classic Fender input.  You can verify this by plugging into each jack.  Jack number two should be noticeably less loud, just like a zillion Fender amps.

I have no idea about wire color, for all we know it wasn't the same amp to amp.  So follow the wire from I over to the main board.  Does it go to a cap, and only to that cap?  Schematic says 0.047uf.

And I suspect it is correct, but verify that G goes to the ground trace.

As to CA, are the two 22k resistors there on the jack board?  Clearly using either jack activates the CA line.  I remain convinced it is a mute.  A mute keeps the amp quiet until something is plugged in.  That would be the only feature of it.  If you do not find it noisy with no instrument connected, then you already have the "feature".

But if you cannot visually trace the circuit, trace it as far as you can with certainty, and note a landmark on the board at the farthest point.  Then try to trace it further.  If you are not sure, use your ohm meter to verify if the next point really is connected to the previous progress.  Zero ohms between two points, means they are connected.  If we can find a connection from CA point to transistor Y, at least we can start from there.

AH, you just posted as I typed.
When you say connects to tip, are you finding the resistance of the 68k or 22k?  Or are you seeing a direct connection.

Don't know what kind of jack it is, but are you saying that both live contacts in it BOTH touch the tip and not one for ring?

Is the jack soldered to a circuit board, or are the loose wires soldered to the jack direct?  If wired, verify the contacts and cutouts have not been reversed.

Theors

The (CA) has the 22k resistors on each jack which contacts each jack Tip. The (I) has two 68k for both jack Tips. Checking ohms while the resistors are on the board, the 22k's read 22k. The 68k's read 34k. But the 68k's off the board read 68k each.

Correct. Both (CA) and (I) touch the Tip.

I've attached pics of the jack. Disregard the large Red & Black wire used for a simple 2 wire jack.
'82 Carvin DC200 + others

Theors

'82 Carvin DC200 + others

Theors

'82 Carvin DC200 + others

g1

  Those jack switches look to be bent in a way that prevents the switching function to work properly.

Theors

Great...if it's that simple. Can you recommend a website where I can order replacements? And what type I should order? I can solder new ones on. It's worth I try
'82 Carvin DC200 + others

Theors

I wouldn't be considering the jacks at all but since I did fiddle with both of them in an effort to snug up the fit.
'82 Carvin DC200 + others

Theors

I think I might have found the culprit. Thanks to g1's remarks. Out here on my phone, pouring over the pictures of the disassembled jack, I can see that the (CA) contact is bent back which allows it to touch the Tip! I don't think it's supposed to! It should be in the (G) position until disengaged by the Sleeve of the cord!!!!
(I feel like Gene Wilder in Willy Wonka!!!)
I shall bend it back this evening to confirm.
The (CA) should never touch the Tip in the first place!!! Wahoooooo!!!!!!

So...you guys think I'm crazy? Or got it solved?
'82 Carvin DC200 + others

J M Fahey

Crazy? ... no.
You have been told this countless times for the last couple days  ::)

Theors

Note to self...DON'T "JACK" WITH AN ALREADY WORKING JACK!!! Especially a fairly complicated one!
Sorry guys. Thank you so much for your patience and help!
'82 Carvin DC200 + others

Theors

I feel the need to explain my stupidity. Cleaning the pots I can do and have done before.  But when I decided to fiddle with the input jacks I had no idea that they were the type of muting jacks or whatever. Nor was I even familiar with that type of input jack. Little did I know the headaches and frustration I would create for myself by trying to adjust the tension by pushing on the tip and the sleeve tongs. Since the Jack is basically enclosed in plastic and soldered to the board the damage is not visible to the eye. Still, even when I removed the Jack from the board and looked inside I didn't understand why two tongs were touching the tip of the cord! Because of my lack of knowledge on what to look for in this type of input jack I just looked at it for hours on end. But when I finally posted a picture of what I was looking at, that's when "g1" said, "Those jack switches look to be bent in a way that prevents the switching function to work properly". What?...jack switches? Good lord! It was staring at me right in the face! Of course!...I pushed on that tong which bent that piece over which now touches the tip! BINGO! How stupid can I be!
Well, A picture is worth a thousand words. I know I would have never discovered this on my own.
Thanks a million to all of you! I definitely learned something.
Jeff O
'82 Carvin DC200 + others

Enzo

Something else to learn.  Looking at the second photo, and any other interior shots of the jack, the two contacts do not both touch the tip, unless they are bent.  That is clearly a TRS jack, and the 22k resistors go to the ring terminals.