Help with 1979 Deluxe Memory Man (chorus not working)

[L5]

Hello everyone,

I have a 1979 EHX Deluxe Memory Man (5 knob version). EH1343 circuit. The problem is with the chorus mode. When switched to chorus, there is a ringing sound that is present everywhere- even the direct output. The only thing that effects the ringing is the level knob. Also, it doesn't sound like the chorus is actually working in the background. Vibrato mode sounds fine- no ringing sound, and a very noticeable vibrato effect.

The pedal is very clean internally. I have inspected the board and cannot find anything obvious. I have an adequate multimeter. Also have a pair of 20MHz scopes, but very limited experience with them. Please help!

(first time poster, please forgive any newbie mistakes or missteps)

[armdnrdy]

Welcome,

This will help us help you. 

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[L5]

Well, unfortunately I cannot find a schematic anywhere for the EH1343. I will keep looking... maybe another version of this pedal has a similar or identical chorus section?

Hoping this isn't a lost cause, but without a schematic I'm feeling stuck. My apologies for being unprepared. I did search for similar problems before posting, with no luck. Hmmm

[L5]

OK, so I referenced a schematic for a different version of this pedal:

http://www.freeinfosociety.com/electronics/schemview.php?id=381

The LFO switch is the chorus/vibrato switch. My pedal has the same capacitor pairs wired in series to the opposite sides of the chorus/vibrato switch. A pair of 1uF capacitors for the vibrato side, and a pair of 4.7uF on the chorus side. Other than these capacitor pairs, there are no differences between the vibrato and chorus functions. Since the vibrato mode sounds fine, logic tells me that my problem lies with one or both of the 4.7uF caps. I will report back. To the workbench!

[armdnrdy]

I believe this is the one you're looking for:





Easier to work with when component designations are included. 

[L5]

FIXED

In the schematic you provided, notice that the only difference between the chorus and vibrato modes are the (C55, C56) capacitor pair and the (C57, C58) capacitor pair, with the (C55, C56) pair active in chorus mode. The originals are 4.7uF at 16V, and I am getting a 14V supply voltage. Rated too close for comfort, in my opinion. Anyway, I replaced that capacitor pair with Tantalums rated at 35V. Hopefully good to go for another 34 years. A bit of AC hum in the background, possibly solved with a 3-prong power cord but I think I'd prefer to leave it original.

Thank you armdnrdy for the nudge in the right direction. Looks like I need to compile some data before starting a thread on my dead Echoflanger.

Hello again to all, glad to be here!

[armdnrdy]

That was too easy!

[L5]

Embarrassingly so...