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Author Topic: Service manual plea -- MXR Omni (or 117 Flanger)
bear

Posts: 153
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Post Service manual plea -- MXR Omni (or 117 Flanger)
on: February 1, 2013, 17:53
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Does anyone have schematics and/or service manual for an MXR Omni rack multi effects unit? Or failing that for the old 117 Flanger with the Reticon SAD1024 BBD?

I've got a problem that a web search shows happens often, but no resolution comes up. When engaged, the chorus/flanger section only passes clean signal, no effected signal. I don't know how to check if the BBD is fried (or have anything else I can plug it into) so I need some starting point for checking it out. It helpfully even seems to have test points, but I don't know what sort of voltages I'm supposed to be looking for.'

Any of you got any docs squirreled away? (These things are so sparse that I'm assuming no one knows how to do this off the top of their head.)

Digital-
Larry

Posts: 192
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Post Re: Service manual plea -- MXR Omni (or 117 Flanger)
on: February 3, 2013, 09:34
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This is based on my experience using BBD for chorus a LONG time ago. It takes a clock signal and an analog input, and delivers the delayed output. The trick is that the input voltage needs to have a DC bias applied to it in order to pass through the chip. If you have a scope, probe the input pin of the BBD and see what's going on there.

It also needs the clock oscillator to be running.

If you don't have a scope, go get one! I can't imagine doing any serious troubleshooting without one. There are some relatively cheap (assuming you put a value on your time) units with a USB interface available or even tiny little handhelds.

bear

Posts: 153
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Post Re: Service manual plea -- MXR Omni (or 117 Flanger)
on: February 3, 2013, 16:48
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I feared a scope would be necessary, but it's probably long overdue. Still need to have an idea of the circuit, though. Modulation stuff is a bit more out of my depth than most stuff.

Digital-
Larry

Posts: 192
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Post Re: Service manual plea -- MXR Omni (or 117 Flanger)
on: February 3, 2013, 18:33
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Here's a schematic of an MXR flanger clone:

https://tinyurl.com/azykeyb

Barring other differences, the clock signal comes into the BBD (A1) at pins 3, 14, 8 and 10. If you're not seeing a square or rectangular signal there then you're totally out of luck as that is what shifts the audio through the circuit.

Regarding a small cheap scope for audio and fx work, this looks promising: https://www.seeedstudio.com/wiki/DSO_Nano_v3 It will measure up to 100 kHz which might be good enough for BBD clocks.

I have a USB scope which I can use with my laptop, so I have not used the DSO Nano 3 personally.

bear

Posts: 153
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Post Re: Service manual plea -- MXR Omni (or 117 Flanger)
on: February 4, 2013, 06:39
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Looks like the scope is a defunct product, but it leads to promising places. I need to figure out what would also do amp tech work -- I like to buy things once when I can.

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