MXR M-167 Stereo Chorus - Command Series [Gutshots]

[Zokk]

Hi
as requested by fellow Govmnt Lacky, let's go with some pictures of the one I have to repair; it has the Reticon SAD512D onboard, and it's not in perfect shape.
All the transistors/FETs are sanded
Diodes are 1N914, trimmer is 250KOhm.

Pictures of a mint unit:
http://www.effectsdatabase.com/model/mx ... reochorus#

Let me know if you need more pictures or info about the one I've on my desk at the moment.

Cheers.

[Govmnt_Lacky]

I wonder how much this chorus shares with the MXR Micro Chorus?

Are you having problems with it OR are you just in need of a schematic?

[Zokk]

Yes this one is defective, I've to make further tests to see if the SAD is still ok, because there's no chorus when the FX is on.
But I'd feel more comfortable if I had a schematic (with the transistors references as well) to guide my steps.

[Govmnt_Lacky]

Well.. there is a lot of testing you can do with a good multi meter to check voltages and a clock input to the 512.

In any case, I have heard that the 512 can be replaced with an R5106 BBD chip.

[Zokk]

Thanks for advice.
I've just came across your post about the other Reticon chips, very interesting if they can be cross refs.

[Scruffie]

Looks pretty micro chorusy to me from a quick cross reference with the schematic... I would think you can use the same schematic for the most part even if there's some minor changes.

[lead2203]

Thanks for advice.
I've just came across your post about the other Reticon chips, very interesting if they can be cross refs.

I kind of hope so. I have a bunch of these and the delays N.O.S. ....that I would like to put together.
If anyone needs more pics ....I can post some more of this one ...and some of the Command Series delay also.

[Fender3D]

Looks pretty micro chorusy to me from a quick cross reference with the schematic... I would think you can use the same schematic for the most part even if there's some minor changes.

Yes, at a first glimpseits the same, but it has an added pot for chorus intensity and an added inverting buffer for stereo output (on the same LFO chip ).
Interestingly MXR inverted both dry and wet signals, I wonder the surprise when you mixed the two channels

[Fender3D]

Zokk,
"bypass" switch shorts wet signal to GND, if it fails might be your issue...
Check for wet signal at Intensity, or whatever is called, pot's lug3

[Zokk]

Yes the micro chorus schematic is very close to this one.
Thanks for the tips about the switch.

I've found the real problem using the scope, it came from the pedal assembly choice: there is way too much mechanical stress on the jacks and pots.
So the already fixed tracks, as you can see on my pictures, have been broken again. Easy fix and a living SAD512D
I also changed all the capacitors (even the ceramic ones) just because I have recived a new cheap desolder iron.

It works fine now, except the signal to noise ratio is awfull when the effect is engaged; and I can't set the trimmer wiper to 4.5V (as I've understood it's the Vbias... am I right?).

Lead223 do you have the same noise problem with yours?

[Fender3D]

Yes, the trimmer will set the bias voltage for both audio AND BBD.
It should be set for a symmetrical distortion from BBD output.

If you look for flanger, chorus, analog echo you'll find alignment procedures here as well on the other forum...

[Zokk]

Thanks for the confirmation.
However it doesn't allow for a fine setup: it has a very limited range, so I can only see distortion at some point in the negative peaks of the signal.
I've ended to let this trimmer in the same postion as it was when I opened the pedal... there's no real adjustement, just rough setting.
Don't know if it's relevant or if I'm trying to monitor the wrong stuff in the circuit (I took measures at pins 3 & 4 on the BBD chip).

But I do see LFO bleedthrought a lot, that could explain the noise and the audible pop when the fx is engaged.
I'm not sure if it's a problem, maybe all these pedals are noisy by design