hi, can any1 help me debug an old wah?voltages within

[bobster]

hi guys ,
ive been working on an old jen wah from the 70s trying to get it working again. pls be aware im very limited in electronic skill but have posted some voltage results which may help some of you to give me an idea where to look for problems.

ok , i have two old jen wahs. one works great so i took voltage readings on it and then took readings on the one thats acting strange to compare.
there is almost no difference in results and all solder joints appear to be ok etc.
the symptoms i get with faulty one are ........
in bypass , no problems
when switch activated , seems to work more like a volume pedal.......but also when pedal depressed downward [ where it would normally be the trebly sound ] it actually gives a large but not particularly pleasant sounding boost in comparison to bypass.
when pedal at opposite end of travel sound is very quiet. frequency doesnt seem to be effected when its switched and i cant hear any sweep from bass to treble when it appears to be acting 'like' volume pedal.
the 4.7 uf electrolytic [ which i believe is implicated in 'volume pedal ' type symptoms ] seems soldered in fine and i tried another new one and got same problem.

ok , voltages- with pedal upside down / opened up looking at circuit board with switch uppermost  input jack on left-
4.7 uf electro cap ,  neg side 0 volts , pos side 0.71v    [ neg side at bottom left of board same orientation as good wah ]
transistor nearest inductor  , left leg 0.11    /   middle leg  4.47   /   right leg  0.7
transistor further to right of board ,   bottom leg    9.52   / middle leg  2.9   /   top leg   3.52
both inductor   legs read  0.71

all wiring is identical to the one that works ok and im really scratching my head on this one !
any ideas?
thanks - bob

[bobster]

bump!

[bside2234]

It's possible your inductor is bad. You could solder some wire from the inductor pads of your working wah over to the pads of the non-working wah and see if you get the wah effect.

[MikeH]

Do you have a schematic?  It would help a little bit.  I know from experience that a bad inductor will cause the 'volume pedal' type symptoms.  I'd check the inductor for continuity; you might have to desolder it to do that

[Paul Marossy]

It's possible your inductor is bad. You could solder some wire from the inductor pads of your working wah over to the pads of the non-working wah and see if you get the wah effect.

Based on my own personal experience, I also agree that it might be the inductor.

[bobster]

hi guys , thanks for replies.
i measured the resistor parallel to the inductor 33k and it is bang on 33k but i am beginning to think the inductor may be at fault. ive tried 3 new electro caps and even tied its neg to ground in case the board was dodgy but no joy .
a shame cos it is a vintage fasel. i'll just have to try another inductor and see if that gets me somewhere.
cheers !
bob

[bobster]

a new inductor got it wahing again! [ and i learned a few things about wahs in the process ]
thanks guys
bob