fixing an MXR Phase 100?

[dubkitty]

i have an ancient script-logo Phase 100 which i bought used back in the 1980s. it's never gotten much use because it's always had a problem, to wit: at the end of every modulation cycle there's an abrupt and extreme glitch in the modulation which expresses as a sort of "weeeeEEEEEEOOOOOOOOOWWWWwwwwww" sound approximately 1/2 to 3/4 of a second long and occurs regardless of other settings. i'd really like to fix it because it's otherwise a lovely-sounding effect. what could cause this problem, and is it something that can be fixed without too much horribleness? if it's not something that's fixable at home, is it worth having someone look at it? or should i just drop back fifteen yards and punt this sucker into the creek? thoughts?

[nbabmf]

There's probably something screwy with the LFO or something drifting out of spec because it's old.

[dubkitty]

it's always been like this ever since i got it circa 1983.

i figure there's some component that's screwed, but i have no idea what it is or how to deduce which one is the problem.

[nbabmf]

Your pedal is as old as I am, and it sounds like it's just as troublesome.

I'd swap the op amps and see if that fixes it.

[dubkitty]

that's what i was thinking. the fact that it always happens at the end of the cycle makes me think it's the last op amp in the chain, but since i don't know much i figured i'd better ask. i just saw someone selling a pair of the TI op amps on eBay for $15. i'll have to check and see if they're the right ones. thanks!

[dubkitty]

it actually turns out that it wasn't anything drastic at all. which is good, since this box is so old that i would dread to do anything to mod it. it's so paleo that all the circuitry is done with solder traces--no printed circuitry at all--and there's no way on earth i would touch that board with a hot iron. i cleaned various bits of the deteriorated grey foam crud that's endemic to old MXR boxes off the components, replaced the broken battery clip which is also a 70s MXR feature, and the box powered up it still had an awful glitchy kind of trebly swoosh when the cycle restarted, though; off to the internets i went, where i quickly discovered that the trim pot on the circuit board controls the center frequency of the phasing. turns out some foo' had turned up the trim pot to the maximum, literally so far that it was stuck. ten minutes of twiddling, and it's New Old Pedal Day. boy, does this thing ever sound delightful run before fuzz

[theavondon]

it actually turns out that it wasn't anything drastic at all. which is good, since this box is so old that i would dread to do anything to mod it. it's so paleo that all the circuitry is done with solder traces--no printed circuitry at all--and there's no way on earth i would touch that board with a hot iron. i cleaned various bits of the deteriorated grey foam crud that's endemic to old MXR boxes off the components, replaced the broken battery clip which is also a 70s MXR feature, and the box powered up it still had an awful glitchy kind of trebly swoosh when the cycle restarted, though; off to the internets i went, where i quickly discovered that the trim pot on the circuit board controls the center frequency of the phasing. turns out some foo' had turned up the trim pot to the maximum, literally so far that it was stuck. ten minutes of twiddling, and it's New Old Pedal Day. boy, does this thing ever sound delightful run before fuzz

Fuck yeah it does.
[youtube]http://www.youtube.com/watch?v=B-XNNowhUZg[/youtube]