Digitech - Multiplay - 20/20 nightmare [schematic]

[petey twofinger]

i modded a multiplay , in the process the expression pedal jack i cut in case shorted . i have been pulling my hair out , rather blindly attemptingg to get it going again , and i feel i may be close ... at this point the switching system is working , thel leds respond .

the odd part , i am getting all the functionality , only it works properly in bypass mode .

the issue is this , in bypass the mixer section of mix control is not operational . it works fine when the led is on and it appears to be engaged but at that point like i said the effect is not present . so when the led is on , the mixer wroks but no echoe , when the led is off , and the effect is SUPPOSED to be bypassed , the effect is present but the mix knob is non functional .

i have replaced two of the j113 , there is one i havent messed with yet . the whole job was a total bodge . this was a long process with plenty of interuptions so i am not sure as far as the prientation of the original transistors , what the pinouts where . i have tried a lot of variations but ...

i also tested voltage on the jfet i have yet to replace . it is reading around 8 on the left pin , ( like looking at the front of a to92 the E ) and 4 on the right pin . this voltage remains constant weather i hit any bypass switches or not . it just isnt so easy to get at , i suppose i shpuld just pull it tomorrow but i was curious if anyone had any assistance to offer me as i am really feeling like a huge dope . i can post the schematic i have i may have to upload them ...


thanks in advance , petey .

[petey twofinger]

here is a pdf of the schematic, i found it challenging to decipher , some info is repeated , digitech may have hastily photocopied this , i am thankful but i have had limited success attempting to discern much from this , thanks to collin at expo anon !!!

[petey twofinger]

i should mention , i have replaced the 4007's , i have a set here ... q8 as well , i have tried a 2n5088 , blindly but i am not even sure about that pinout ... man i reall =y screwed the pooch on this one . i could use some gut shots ...

[Fender3D]

Hi Pete,

in PDS pedals Digitech doesn't use a real bypass system,
they just kill wet signal.

How?
by shorting NE570's pin1 to GND (by Q11).
Q8 simply disengages the mix control when "effect off", so mix pot doesn't interfere with dry signal.

At this point... if mix control behave as it should

in bypass the mixer section of mix control is not operational . it works fine when the led is on and it appears to be engaged

then Q8 is fine...
check the voltage at Q11, it should change when bypassing (more positive when in bypass).
If it doesn't change, check U3 or its neighbours...

As a side note, I know Digitech swapped the resistors ladder in their pedals, please can you confirm RN1 is 5K ladder?

[petey twofinger]

i apologize for over typing , should have been more clear .

in bypas the mixer is operational !

not bypass = no effect no mixer !

bpass mode i have effect , but no mixer . ( it is backward box ) lol

i have sockets in for q 8 9 10 11 , and i have tried new 4007 chips in u3 and u4 .

[petey twofinger]

o , i should also mention , the ne570 is good , as i sapper it in a pds 1002 .

[petey twofinger]

at this point , i have it all functioning but the effect is cutting out ....intermittent

[Fender3D]

Ok,
what if you pull Q11 off?
You should have effect both in bypass and engaged.


please can you confirm if RN1 is a 5K (502) ladder?

[Fender3D]

Sorry for double post,

if the effect is intermittent, it may be an issue with P2 feeding a wrong bias voltage to U18...