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Last Vibro King question..I promise

pfrischmann

Member
Messages
3,356
I got the amp working and I think it sounds great! Now the vibrato doesn't work.

The cells are not lighting anymore.

Any suggestons on how I should test?

This mod should have been nowhere near the vibrato circuit...

Thanks again,
Paul
 

fullerplast

Senior Member
Messages
6,781
Just a WA guess, but did you plug the footswitch back in and make sure it was turned on? Many Fenders require the switch or a shorting plug to work...
 

pfrischmann

Member
Messages
3,356
Hi Fullerplast,

Thanks for all the help BTW. I really appreciate it.

I tried the footswitch. It works for the fat boost function but does not work for the vibrato. When engaged it just makes a pop. I should note when I turn up the intensity, you can hear the amp volume go down. I would think this would indicate that the vibrato circuit is still in the loop.

I wonder if I blew the optoisolator or if it just ran out of life....seems a little too coincidental
 

fullerplast

Senior Member
Messages
6,781
Try replacing or swapping V6 (12AX7). If that doesn't do it, you'll need to look further into the circuit. It's possible the trem roach has gone, you may be able to see it pulsate if you look at it from the side in low light.
 

pfrischmann

Member
Messages
3,356
Thanks for responding Fullerplast..Not yet. I've been a little limited in time lately (New baby). I did try swaping the 12AX7's, no luck. I'm going to see if the lamp is getting voltage and work my way back.

If I opened the circuit in the footswitch so as to make it impossible for the tremolo to be engaged (bad soldering). Would the lamp still be pulsating, just out of the audio path?

In other words. Is the lamp ALWAYS pulsating?

Thanks,
Paul
 

pfrischmann

Member
Messages
3,356
darn,
I measured the plate voltage on v6 A and B to see if there was a swing in voltage. Steady as a rock..There is also voltage present at the bulb side of the roach. The bulb does not work however.

What actually makes the bulb blink anyway?

Thanks,
Paul
 

fullerplast

Senior Member
Messages
6,781
Hi Paul,

The circuit is just an oscillator causing the light to blink. It should blink whenever the footswitch is engaged, even if you don't hear it (when the intensity is turned down).

I just took a look at the circuit again and I think I found a spot you should check. There should be a connection between R58 (the other side goes to the treble pot wiper) and one lug on the intesity pot. This should also be connected to C11. Note that this is exactly where you were working and is the resistor you originally asked about!! I bet you find the problem very quickly....
 

pfrischmann

Member
Messages
3,356
Hi fullerplast.
I may have to do a little more digging. I'm still struggling with the schematics but learning a lot as I go.

If I follow the physical layout, I see R58 going to r57 going to the foot switch. The other side or R58 goes to CB5.

If I follow the treble pot, The center post goes to R68 then to C11 then to pin 6 of v5.

Did they goof the schematic?

I did replace r58 with an 820 ohm. Should it have been R68?

Thanks,
Paul
 

pfrischmann

Member
Messages
3,356
I went to fender and had to blow up the schematic like 200% but I think that's where I goofed. I'm going to be heading to the electronic store on my luch hour tomorrow. Can anybody tell me what R58 should be???

I can't find it on the schematic and wouldn't be sure I could read it accurately id I saw it.

Thanks,
Paul
 

fullerplast

Senior Member
Messages
6,781
Originally posted by pfrischmann
I went to fender and had to blow up the schematic like 200% but I think that's where I goofed. I'm going to be heading to the electronic store on my luch hour tomorrow. Can anybody tell me what R58 should be???

I can't find it on the schematic and wouldn't be sure I could read it accurately id I saw it.

Thanks,
Paul
Hi Paul,

It's really hard to read the number on the scanned schematic, but the resistor you should have swapped was the 100K going to the treble pot..it looked like it was labled R58, but it could be R68. Looking at the resistor you just described, that should be a 2.2M resistor and it is connected to R57 on one side and the diode CR5, C22, and the bias pot on the other side. I think you simply swapped the wrong one...
 

pfrischmann

Member
Messages
3,356
WOOHOOO!

:dude

She is working now!. I have to spend a little more time at volume to make sure everything is cool but I thing we found it!!

Thanks again Fullerplast, Yo da' man!
 

fullerplast

Senior Member
Messages
6,781
Nice work Paul!:dude

After you get a chance to evaluate the mods maybe you can let us know what you think. Did they do what you wanted?
 




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