Mellotronists

Hi everyone-
I found a problem with my M400 I hadn't noticed
before. I'm getting ready to tear it down for bearing
replacment & headblock cable replacement, so this may
be a good time for other fixes. There is some hum
present all the time in the audio output. It varies
with the volume control. Probably need some power
supply caps changed, which I will check. Motor noise
creeps in at a very low level, too.
Here is the main issue. The hum increases on
tracks A and C, and is lower on B. It also does this
when manually moving the headblock without the track
selector linkage engaged to the pin (left of
headblock). Slight movement of the headblock cable
doesn't affect this hum process. I haven't removed
the headblock yet, but I bet the problem is related.
Is there a sliding ground/chassis contact gone bad?

Thanks
-Bruce Daily
M400 #1221

PS- Happy birthday Mr. Wakeman!!





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> Here is the main issue. The hum increases on
>tracks A and C, and is lower on B. It also does this
>when manually moving the headblock without the track
>selector linkage engaged to the pin (left of
>headblock). Slight movement of the headblock cable
>doesn't affect this hum process. I haven't removed
>the headblock yet, but I bet the problem is related.
>Is there a sliding ground/chassis contact gone bad?

You may want to look at:

http://www.kleonard.com/mellotron/vt0206/work.htm

"Typical Korb Mods", #3. Even though it "shouldn't" cause noise
issues, it does in some cases (however it's crackling, usually, not
necessarily a hum).

If that's not it, see if there's anything applicable here:

http://www.mellotron.com/tech.htm

I have an SMS-4 in #805, and I performed a low noise mod outlined on
that page. Hum gone.

ALSO...Radio reception. First, uncoil the coily ground wire going
from the harness to the frame---that's a great antenna. You can also
reorient the machine or move it to a different location. If that
doesn't work, you'll wind up filling your machine with grounded
aluminum foil and/or covering it with a grounded aluminum jacket (ask
Lee R. all about that...it worked, but in order to solve his problem
permanently, he picked up his machine and moved to Hawaii away from
the radio towers! ;-) ).

...kl...
M400 #805 - unhummed
M400 #1037 - uncoiled

** Ken Leonard - Web Table of Contents: http://www.kleonard.com
** Get Outdoors New England: http://www.GONewEngland.org

> Here is the main issue. The hum increases on
>tracks A and C, and is lower on B. It also does this
>when manually moving the headblock without the track
>selector linkage engaged to the pin (left of
>headblock). Slight movement of the headblock cable
>doesn't affect this hum process. I haven't removed
>the headblock yet, but I bet the problem is related.
>Is there a sliding ground/chassis contact gone bad?

You may want to look at:

http://www.kleonard.com/mellotron/vt0206/work.htm

"Typical Korb Mods", #3. Even though it "shouldn't" cause noise
issues, it does in some cases (however it's crackling, usually, not
necessarily a hum).

If that's not it, see if there's anything applicable here:

http://www.mellotron.com/tech.htm

I have an SMS-4 in #805, and I performed a low noise mod outlined on
that page. Hum gone.

ALSO...Radio reception. First, uncoil the coily ground wire going
from the harness to the frame---that's a great antenna. You can also
reorient the machine or move it to a different location. If that
doesn't work, you'll wind up filling your machine with grounded
aluminum foil and/or covering it with a grounded aluminum jacket (ask
Lee R. all about that...it worked, but in order to solve his problem
permanently, he picked up his machine and moved to Hawaii away from
the radio towers! ;-) ).

...kl...
M400 #805 - unhummed
M400 #1037 - uncoiled

** Ken Leonard - Web Table of Contents: http://www.kleonard.com
** Get Outdoors New England: http://www.GONewEngland.org

Hi-
Thanks to all for the suggestions. It makes sense
that the headblock is an isolated ground system, and I
will run with that.

Cheers and beers

-Bruce Daily




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