Carvin Legacy Help Needed!

[pontiacpete]

The guitar cable and the cable to the audio gen are different and do work, in other amps that, is. When inserting an open 1/4" jack into either return or send the sound comes back but the volume is a lot lower that this amp can do. I don't know why this is so, I just happened on it. All the controls in both channels work with a 1/4" jack in send or return jacks.
Now I'm still follow a signal around the circuit. There is a very small distorted signal on pin 2 or v3 and pin 6

[pontiacpete]

Chuck, the signal at P6, which i just figured out what you meant by P6 and 9, is good. There is a definite change in it at pin 7 of v3.
I'm confused as to how the signal goes to c37 on the schematic, can you or someone explain how it gets to the grid of v3?

THANks

[pontiacpete]

"I'm confused as to how the signal goes to c37 on the schematic, can you or someone explain how it gets to the grid of v3?"

B1

[Chuck H]

There is a very small distorted signal on pin 2 or v3 and pin 6

You did that on purpose, didn't you?

[Chuck H]

I'm confused as to how the signal goes to c37 on the schematic, can you or someone explain how it gets to the grid of v3?

With nothing plugged into the effects loop the jacks should have an internal switch system that bridges the signal across the hot leads of the send and return. When something is plugged into either of the jacks this bridge is faulted. There should be nothing but minor signal bleed getting to the C37 with an open jack in either the send or return. Something is clearly cattywhompus because there is no other system in the amp that could fail and cause signal to bypass the effects loop. Something is plainly wired wrong. Is this an amp you or someone else has worked on? If yes, do you know what was worked on? If you don't know then you have an unfortunate and daunting task to verify that all schematic pathways that could be involved are actually going to where they should. I, for one, would be interested in any history available on the amp. Did it ever work correctly to your knowledge? How did you come to be working on it and what were you told about the amp? Etc.

[g1]

Your signal is AC so it goes through C37 to the grid of V3.
How about listing your DC voltages at V3 pins 1,2,3,6,7, and 8.

As far as the signal getting around the loop, you could have a solder bridge across some jack contacts, or across some ribbon cable connections.
Or I suppose the signal could be bleeding through the power supply.

[pontiacpete]

Here are the DC voltages
pin 1 161
pin 2 0
pin 3 1
pin 4 2.7
pin 5 2.7
pin 6 214
pin 7 0
pin 8 1.2
pin 9 2.7
(DC heaters)

[g1]

Looking at V3A, pin 1 and 3 voltages don't agree with each other, pin 1 is shown as 280V on the schematic. Check value of R31 and R41. Can you lift 1 leg of C59 and recheck pin 1 & 3 voltage? For now I'm ignoring the FX loop weirdness.

[pontiacpete]

R31 looks good it's 220k resistor, it measures 230K. I believe the schematic I originally attached has 100k. Here's the one that's closest to this amp. There's another change to this one also, C69 is 22uf not 10uf.
R41 looks good also, at 900ohms.
With C59 lifted the voltages don't change. 1v on the cathode and 160v on the plate.

thanks.

Is it possible that i put the wrong return and send jacks in?
i Need to check all the connections.

[pontiacpete]

R82 4.7m resistor was open. It read -4.7m on way and the other 50m. I had thought this was strange but should have lifted one leg a long time ago to test. Oh well

[g1]

Good! Unfortunate that the reading across Q5 in parallel just happened to be 4.7M, which lead you to overlook it. So Q5 wasn't getting biased on, but when you hit it with a big enough signal it was turning on.
I'm assuming it is working fine now, but still wondering about the FX loop not cutting out the signal when something is plugged into the send or return.
(P.S. Those V3 readings are good for 220K plate resistor, schematic appears to have wrong voltage listed.)

[Chuck H]

but still wondering about the FX loop not cutting out the signal when something is plugged into the send or return.

Yupper. Since those jacks were replaced I would be double checking the wiring and switching functions.

[pontiacpete]

The FX loop is working fine now too. yay!! When plugging into either jack with the open 1/4" the signal is cut to practically nothing. There is a little bleeding thru but not nearly as much as before.