73 Silverface Bronco-vibrato not oscillating

[stratguy2015]

Hey guys. This is a repeat post from last night. I didnt get many suggestions on how to fix this, so I'll try again on this larger thread.
I have a 73 Fender Bronco Silverface and the vibrato does not seem to want to oscillate. When I turn the intensity knob I get a change in voltage like I should but the circuit itself is not working. I'm going off of the AB764 schematic. I've changed the main can cap, the three caps in the vibrato circuit, a few resistors off of that. Still no vibrato. I checked the newly installed the caps in the vibro circuit, they are all good.

Here are some voltages:
Fender schematic AB764.
V1 VOLTAGES. MY VOLTAGES (V1)
PIN#1- 255V. PIN#1- 259V
PIN#3 - 1.9 V. PIN#3- 1.93V
PIN#6- 260V. PIN#6- 251V
PIN#8- 1.7V. PIN#8- 1.88

V2 VOLTAGES
FENDER. MY VOLTAGES (V2)
PIN#1- 210V. (FLUC) PIN#1- 133V(STEADY
PIN#3- 2V (FLUC) PIN#3- 2.87V(STEADY
PIN#6- 410 V. PIN#6- 414V
PIN#8- 216V (FLUC) PIN#8- 189V (STEADY

When I turn the intensity pot while I was checking the V2 voltages, there was a swing but the vibrato doesn't seem to be oscillating on its own. Have tried several different tubes. Where can I go from here? Any help is hugely appreciated!

 

[stratguy2015]

Now that I look at it V2 pin#1 seems very low. I have 133 volts and the schematic calls for 210 volts. I did change the 470k resistor from pin#6 to pin#1 on V2. Maybe I should decrease it so my voltage comes up to near 210v?

 

[stratguy2015]

So when I turn the Intensity pot all the way down I get around 206 volts on Pin#1 V2. I did put in a 1k main bias resistor replacing the 470k. I'm not sure how much of an effect that would have since I'm getting a constant voltage of around 410 at Pin#6 V2 anyway. I'm stumped

 

[stratguy2015]

Excuse me not the 470k a 470ohm bias resistor

 

[schmee]

voltages are often way off in many fender amps in that area. DO you have the footswitch plugged in? Test both ways.
It's often the opti occillator that's the issue, but can be any of the nearby resistors or caps too. If those test close, I usually just pop in an opti and it is most often the solution. Cheaper than time.

 

[stratguy2015]

voltages are often way off in many fender amps in that area. DO you have the footswitch plugged in? Test both ways.
It's often the opti occillator that's the issue, but can be any of the nearby resistors or caps too. If those test close, I usually just pop in an opti and it is most often the solution. Cheaper than time.

This amp doesn't need the footswitch for the vibrato. No opti in this circuit either from my understanding

 

[Ten Over]

Hey guys. This is a repeat post from last night. I didnt get many suggestions on how to fix this, so I'll try again on this larger thread.

Well, you still haven't answered my question and you still haven't posted the voltage I wanted.

 

[stratguy2015]

Well, you still haven't answered my question and you still haven't posted the voltage I wanted.

Probably on the last post. Can u refresh my memory?

 

[Ten Over]

Now that I look at it V2 pin#1 seems very low. I have 133 volts and the schematic calls for 210 volts. I did change the 470k resistor from pin#6 to pin#1 on V2. Maybe I should decrease it so my voltage comes up to near 210v?

No. There is no reason to believe that there is 133V on V2 pin#1.

 

[Ten Over]

Probably on the last post. Can u refresh my memory?

What meter are you using?
What is the voltage from V2 pin #1 to V2 pin #8?

 

[stratguy2015]

I'm getting 133 volts at V2 pin#1. When I turn the intensity all the way off I get 210 volts at V2pin#1.
V2pin#1 to V2 pin#8 measurement is 0 volts

 

[stratguy2015]

Using a Klein MM420 voltmeter

 

[stratguy2015]

What meter are you using?
What is the voltage from V2 pin #1 to V2 pin #8?

I'm getting 133 volts at V2 pin#1. When I turn the intensity all the way off I get 210 volts at V2pin#1.
V2pin#1 to V2 pin#8 measurement is 0 volts

 

[Ten Over]

Using a Klein MM420 voltmeter

They say that it has a 10M input impedance, so that shouldn't be throwing the voltage measurements.

 

[Ten Over]

Did you try a different 12AX7 in V2?

Some pictures could help at this point.

 

[stratguy2015]

Did you try a different 12AX7 in V2?

Some pictures could help at this point.

I did swap tubes already. Here are some pics:

 

[Ten Over]

The brown wire should go from the 68k resistor to the wiper of the Intensity pot.

The Speed pot should have a jumper from the wiper to the lug with the 100k resistor.

 

[schmee]

This amp doesn't need the footswitch for the vibrato. No opti in this circuit either from my understanding

Oh yeah, this is the Champ like amp. I had Bantam Bass on the brain... which has no vibrato at all! haha

 

[stratguy2015]

The brown wire should go from the 68k resistor to the wiper of the Intensity pot.

The Speed pot should have a jumper from the wiper to the lug with the 100k resistor.

 

[stratguy2015]

Moved the brown wire to the 68k resistor. Have vibrato now. Thank you. No speed control. And the middle lug is tied together with the resistor already attached. From middle lug to side lug?