Help me fix a Boss CH-1 Super Chorus

[ianmgull]

I have a CH-1. It passes signal but there is no chorus sound EXCEPT:

When I turn the depth knob back and forth i get a chorus sound. This leads me to believe that whatever is responsible for generating the sweep LFO inside the pedal has gone bad. Is this what the clock driver (mn3101) does? I can take voltages if that would help as well. Thanks!

Schem:

http://www.freeinfosociety.com/electronics/schemview.php?id=2290

[ElectricDruid]

It does sound a bit like your supposition might be right - the sweep LFO is dead. If it were outputting a constant voltage, varying the depth control would vary that voltage and make a chorus. Your manual twiddling replacing the LFO, basically.

It's not the clock driver MN3101 that's at fault though. That drives the delay line, and if it had gone, you'd get no delayed signal at all, and no chorus in any situation. Instead you want to look at the 8-pin dual op-amp IC4a/4b and its associated components.

There's a pair of back-to-back 10uF capacitors C26 & C27. I'll bet those are tantalum bead capacitors (big values in small packages -ideal for effects). But the trouble with tantalum caps is that they hate being reverse polarised even briefly, and will die if this happens. I'd be pretty suspicious of them.

Another possibility is a broken connection to the Rate pot. That would kill the LFO, and mechanical failures are more common than electronic failures by a wide margin in my experience.

Good luck,
Tom

[Mark Hammer]

Tom's description and suggestions get my vote.

[T1bbles]

My mate had this exact problem with an Ibanez CF-7, I believe it happened after he (well it was me actually but don't tell anyone) accidentally popped a reverse polarity supply into it, so yea, check those tants!

EDIT: Come to think of it, they should really stick diodes in the LFO circuit to block any reverse polairty power. Makes perfect sense to me.

[ianmgull]

Thanks for the suggestions. I've hit a stumbling-block. After getting this pedal and being convinced I could figure it out it turns out the version I have is much newer, and nearly all surface mount. What's more, I don't even see a separate mn3101 and 3007 ( I think they may have been condensed into the large 28 pin?) Anybody have a schem for this version? I don't know what anything is now...

[rustypinto]

This is definitely the digital version of the CE-1 (as opposed to the analog version with the MN3007).

I could not track down the schematic myself. From what you said, the DSP is still delaying since you can make chorus tones by modulating the rate knob by hand. I would trace out the connections from that potentiometer and try to figure out who the modulating IC is, then debug it from there.

Can you tell us the first number on IC1 (under the orange mark)? The second portion looks like "0541-DEEP," but thats usually die rev. or manufacturing type markings. I'm just curious what this DSP is.

[ElectricDruid]

Groan!

This is much worse! We stood a pretty good shot of fixing an old one, but this is a whole load more difficult.
Still, it isn't impossible, so let us know what you find out.

Sorry!

Tom