Deluxe reverb V5 pin readings way off

[Doc Stitches]

Keep in mind this 75 DR was greatly modded and I am working to restore it to AB763....I hope.....

Problem is no tone controls working ( at all )....on either channel. Volume is great.....very loud ) on #2 and gets more distorted as I turn it up....like background scratchy.

I can find no grounding problems at pots or board.

Maybe pin info on V5 will help :

1 = 440v
2 = 42v
3 = 0v
4/5= 3.5v
6 = 392v
7 = 43v
8 = 0v

What might be the cause of pin 1 being so high ?.... bad tremolo cap ?

Should I send some pictures ?

forgot to ad.... PT voltages to rectifier tube :

pin 2 & 8 = 458

pin 4 & 6 = 357



Thanks
Doc

[Enzo]

Yeah, the plates read so high because the tube is not conducting. Note the cathode voltages at zero?

Pins 2 and 7 at 42v? Are you sure? Are you sure that is not -42v instead?


Now plug a footswitch into the vibrato jack to turn it on, or just use a clip wire to gro0und that jack. That turns the trem on, and your voltages hould fall into line.


Meanwhile, V5 is the trem tube, and not likely involved in tone control issues.


Tone controls:
Turn the bass controls to their end so they are acting as zero ohms. Now measure resistance to chassis from the bass control. Get 6800 ohms?

[Doc Stitches]

You're right Enzo.... 2 and 7 are -41v
Foot switch in vibrato jack ... readings are good....except pin 8 is 15v

Both bass controls read :
6700 ohms at 1
0 ohms at 10..............

[Doc Stitches]

pictures DR

here are pictures :

[Enzo]

Both bass controls read :
6700 ohms at 1
0 ohms at 10..............

So go look at your AB763 schematic. (In fact, the layout for this schematic is also widely available, compare your wiring to that) Not the bass control is in the center of the stack, the 6800 ohm resistor taking the place of a mid control. Note also that neither end of the bass control is grounded. Yet you get zero ohms to ground at one end setting. That tells us you have something wired wrong.

[Doc Stitches]

Thanks Enzo.

OK...I have the schematic which I have been following but I'll get the layout and see if that points to my problem.

[Doc Stitches]

OK....I pulled out the normal channel inputs and pots of another original 65 Deluxe Reverb and all wiring is correct......maybe I have a bad pot ?

[Enzo]

Let us get on the same page, so to speak. Looking at the Deluxe Reverb AB763. Your problem is the tone controls have no effect, yes? Both channels the same, so whatever is wrong would seem to be wrong with both.

Look at the schematic, you see the 6800 resistor from ground to the lower end of ther bass control, the top of the bass control wired to the bottom of the treble control. Ground your meter black probe to the chassis. Power off of course. Now look at the layout drawing. The controls at the top. I usually work with the controls towards me, but let us stick with the way it is drawn, so set your amp chassis that way.

Measure the chanel 1 controls, the ones to upper right. On the bass control, the one next to the other channel jacks, the left terminal of the bass control has the 6800 ohm to ground. With your red probe, measure the ground end of the 6800 ohm resistor. It SHOULD measure zero ohms. After all it is grounded to the pot body is it not? If you do not get zero ohms, then ther is a mising ground connections, perhaps the pot body is not grounding to chassis. If that is OK, go to the top of the resistor at the left terminal. SHould get 6800 ohms, regardless of bass control setting. Do you?

NOw move red probe to the center terminal of bass control. What readings? It SHOULD vary from 6800 ohms all the way to one end, then turn the control to the other extreme and we should see about 256.8k. We won't, because the parallel path through the treble and volume controls will bring it down somewhat. But we should never see zero ohms to ground. Remember, the black probe stays on the chassis.

[Doc Stitches]

DR tone problem

Enzo..............thanks for the "same page" tutorial...........following every detail of your advice everything checks out OK.

Problem remains : Both tone controls have no effect........correct ohm readings as described, pot body grounded, ground end of 6800 resistor measures zero

top of resister at left terminal gets 6800 ohms regardless of bass control setting.

Center terminal of of bass control reads from 6800 to about 256.8k... ( turned from one extreme to the other )

[Enzo]

OK then. Your earlier report confused me. SO the resistor wiring seems OK.

Might as well also verify the connections to the treble controls are all OK.

If the tone controls have zero effect, and both channels are affected, then I am led to suspect some consistent error. I could be wrong. Missing slope resistor, wrong value resistor. Believe me you and I would not be the first nor last people to ever install a 470 OHM resistor in place of a 470k one. or something similar

[Doc Stitches]

Good call on the 470 resistors values, missing resistors ( who, ME ??? ) ......... I'll re, re, re, recheck em.

By the way...... I have NOT made a mistake................since the last one !

[g1]

Behind your channel 1 input jacks, at the far end of the board there are 3 wires, appear to be brown, blue, and white. Where are they going? From the pic I don't see them connected to the pots, can you post a pic showing more of the pot connections?
Are you comparing to this layout?

[Doc Stitches]

DR more pics

[g1]

Appears to be wired correct from what I can see. Make sure no pot lugs are touching each other or the casings. Are all pots tight to chassis? No breaks or loose ground wires (the bare ones from the brass plate to the board) ?
What happens to the sound when both bass and treble are turned all the way down?
Did they work before you started rewiring?
Like Enzo said, it would have to be the same error done to both channels, not likely that a fault could occur to both channels at the same time. You mentioned it was heavily modded, could this be a mod done with wires on the underside of the board? (sorry if I'm grasping at straws a little here but people do strange things sometimes)

[Doc Stitches]

this is becoming a real mystery.........no pot lugs touching, pots tight to chassis, no breaks or loose ground wires.

I will try the bass/treble test and get back to you g-gone...........

I do not know if it worked before I got it..transformer was out.no tubes, wire and extra pots and inputs.

I have had the board opened up and saw nothing unusual except too much solder at many joints.... but did not see anything else out of place. You think the solder touching the bottom board could cause this issue ?

Keep grasping at those straws !!!....it is helping me think "outside the box".could the wrong PT cause this, or anything else not in the tone signal path ???....a bad volume pot ?

I have done the chopsticks test to no avail............ I am still working on the ENZO resistor retest

I forgot to mention....there is a waxy looking substance all over the top of tagboard....what is it ???