Author Topic: MXR EVH flanger...help !  (Read 368 times)

artstomp

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MXR EVH flanger...help !
« on: May 09, 2019, 04:24:20 AM »
Iím trying to repair an MXR EVH flanger for my sonís friend...when powered on, you can hear the LFO sweeping loudly...in bypass mode the sweeping bleeds also. The BBD chip, MN3204 works fine ( i guess ) because as i turn the clock trimmer clockwise all the way, then turn counter clockwise, it is now flanging 100% as it should...no audible changes heard when the bias trimmer is turned in any position.
    But as I reset the power...the flanging was gone, LFO again is heard sweeping loudly again....and when i repeat turning the clock trimmer as describe earlier...flanging now occurs normally.
   As the EVH boards is SMT, thereís not much i can replace. I swapped out an MN3207 as it has the same pin config but has a higher delay stages...just to test somehow if the MN3204 is defective in some way. But same scenario happens with the MN3207. ( tho it ďflangeĒ in a different way ).
   Any suggestions where should i look. Tnx in advance.

Scruffie

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Re: MXR EVH flanger...help !
« Reply #1 on: May 09, 2019, 05:24:14 AM »
Got some photos? There's no schematic so going to have to take a bit of a stab at how it works.

But you've determined the LFO works and the BBD so the clock works which leaves an issue between the LFO and whatever kind of VCO it uses.
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somnif

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Re: MXR EVH flanger...help !
« Reply #2 on: May 09, 2019, 05:36:33 AM »
Got some photos? There's no schematic so going to have to take a bit of a stab at how it works.

But you've determined the LFO works and the BBD so the clock works which leaves an issue between the LFO and whatever kind of VCO it uses.

I'm pretty sure its based on the MXR 117 Flanger (its model number is "EVH-117"), for what that's worth.

artstomp

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Re: MXR EVH flanger...help !
« Reply #3 on: May 10, 2019, 05:54:39 AM »
Here's the gut shot Scruffie !....the vintage 117 flanger of course uses the SAD1024 BBD...

tnx for trying to help !
« Last Edit: May 10, 2019, 05:59:10 AM by artstomp »

Scruffie

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Re: MXR EVH flanger...help !
« Reply #4 on: May 10, 2019, 08:09:50 AM »
The vintage also uses 1024 stages and doesn't have a compander so quite a different circuit overall! But some nice design nonetheless.

I think I misunderstood your diagnosis, are you saying if you play with the clock trimmer the pedal works on its own until you reapply power or that you can just manually sweep it?

The former, could be a bad electro or solder joint, the latter... probably one of Q1-5 are bust (from the location of the range trimmer I assume that's the VCO). But without a schematic or tracing the whole thing :-\
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artstomp

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Re: MXR EVH flanger...help !
« Reply #5 on: May 10, 2019, 08:23:03 PM »
Thanks Scruffie...the flanger works on its own after readjusting the clock trimmer..( i leave it on that position ) as if nothing is is defective...when power is turned off, then turned on again...it will no longer flange!...ill have to readjust the clock trimmer again to make it work again...yes itís hard to trace w/o schematic...
By the way, i already replaced some electrocaps...those 4 in horizontal position.

Note: as a i momentarily shorts the clock trimmerís pin 2 & 3 it works as it should...until the power is reset again..
« Last Edit: May 10, 2019, 09:04:59 PM by artstomp »

zgrav

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Re: MXR EVH flanger...help !
« Reply #6 on: May 15, 2019, 08:26:05 AM »
It sounds like a cold soldered connection to me too.  I would reflow the solder on the clock trimmer just in case the process of adjusting it is re-establishing a temporary connection.