M102 vibrato very loud

[Juan]

...continuation of my M-102 project.
1) Huge volume increase when the vibrato tab is ON. Only the Vib chorus works and it is distorted. The Vib small, Vib celest and Vib celest II seem to be inop. Same both upper and lower manuals.

2) Reverb is extremely wet. Crazy wet. AO44 - If there is an adjust pot I can't find it.

Thoughts on these?

[enor]

1. Probably a bad ground at the vibrato delay line
2. No adjustment per se. Are the compressing light bulbs both still good?

[enor]

1. Probably a bad ground at the vibrato delay line
2. No adjustment per se. Are the compressing light bulbs both still good?

[Juan]

I will check the bulbs in the reverb amp and report.
I'm not sure how to check the ground at the vibrato delay line.

[Juan]

Test report: Two bulbs in reverb. Both inop. Then both bulbs very on faint, then both bulbs on like a blow torch when I turned on the vibrato.... now both seem to be faint but working correctly. What the heck?

[muckelroy]

I thought there was a gain pot in the AO-44. It requires a tweaker flathead screwdriver to turn it, if you still need to adjust the level. It should be accessible from the back of the chassis.

[Juan]

No gain pot on this AO-44 itself.

[Juan]

Here is a little video of the issue with the vibrato. Is this a resistor problem?
https://youtu.be/fI3tVS7vSWE

[geoffbrown]

The AO29 has a volume balance between vib and non vib channels set up by the factory, if the non vib channel is significantly lower in volume, it could be caused by R26 R27 changing from original specs.download the service manual and all will become clear.

[Juan]

Thanks for the info. I have a hard copy of the service manual. I found exactly what you said. Definitely needed the bifocals. I'm not an electrical guy. Does the unbalanced symptom suggest the resistor is open?

[geoffbrown]

Reducing the value of R26 gives more volume and a brighter shrill sounding nonvib channel which some people may not like, increasing the value of R27 gives more nonvib volume

[enor]

If this is caused by that resistor, it would mean that it's gone lower - not opened up. Which I guess can happen but not very commonly. Still, easy to check!