Sick Phase 90

[Davefx]

Just got around to cleaning up this old phase 90 that appears to have had a beer or soda permeate the board.. ugh.  It's got rotted foam, green traces and joints, etc.  You can sort of hear it try to phase, but no slow phase, kinda like the LFO is froze in one position, and yet you can get a slight "warble" phase at high speed.

What do ya think, remove all the components, clean the board and reload with fresh parts? Or just make a new board?  I have no idea what the proper waveforms would look like on a scope, to even attempt to troubleshoot  I would like to see it live again.

Comments, curses, suggestions, anyone?

[ExpAnonColin]

Hmm...  As long as all of the traces and components are in tact and in the right places, for the most part, the circuit will probably work.  Maybe you should go in with a DMM and check components to see if any of them are broken.  How bad is the board?  If it's just sort of beat up, you could probably get by with it, but I mean, if all of the traces are in tact and the PCB isn't broken, then it's probably a component problem (probably).  

-Colin

[Davefx]

Thanks Colin...  That's what frightens me, a bad component!! LOL!!  I'm just intimidated by an unfamiliar circuit.  I guess the only thing that I'm unsure of is testing the Jfets in circuit.  I think there IS hope for the board, but touching up some of the solder joints is difficult because they are so contaminated.  It would be nice if someone had a voltage chart at least, that i could go by, that would help.

Thanks

[Davefx]

Oh, incidentally, it is one of the last originall MXR's. With TL062's.

[ExpAnonColin]

Man, that's pretty depressing-what happened to it?  Where'd you get it?

I'm not too familiar at all with the Phase 90 at all, but here are a few schematics and whatnot that might help:
http://tonepad.com/project.asp?id=7
Be sure to check out the build reports, that might help too.  Hope someone else who knows the circuit better comes along...

-Colin

[Davefx]

Ack!!! Colin!  FP's layout has 7 trannies total, mine has 9 and some are un readable...    Oh well, time to build a new board!!  Yes, I give up easily..

[bwanasonic]

I'd try giving it a good cleaning first. Some gunk on the board might just be shorting something out.  A toothbush and some alchohol might help.

Kerry M

[Davefx]

Well I'm going to get a tooth brush for the occasion and run to the store because I ran outa alcohol.. Then I'll give up!! :lol: No, but seriously 2 of the trannies on this thing are blank, as if the # was sanded off of it. I need to find an original schem if possible.

[AL]

I've had luck in the past using a pencil eraser to clean boards.  Just be careful not to apply too much pressure and crack the board.

AL

[bwanasonic]

Ack!!! Colin!  FP's layout has 7 trannies total, mine has 9 and some are un readable...    Oh well, time to build a new board!!  Yes, I give up easily..

I'm pretty sure there are only 5 transistors in the tonepad layout? Are you sure those are all transistors? Even the Phase 100 only has 5.

Kerry M

[Ed Rembold]

Dave,
I think you meant "it's a later version w/TLO61's".
as the early "script logo" P90's used 741's.
Anyway, R.G.'s schem @ GEO is correct for your version.
Dig in , but I doubt you need to build a new board.
Trim pot may need tweeking/replacement.
Ed R.

[gez]

You can sort of hear it try to phase, but no slow phase, kinda like the LFO is froze in one position, and yet you can get a slight "warble" phase at high speed

Try cleaning the pot which sets the speed of the LFO (and all the other pots for that matter).

[Davefx]

Right guys, after looking closer, there are only 5 trannies, the others are "2 legged" and look like trannies (diodes ?)  And Ed, I have Tl062's on mine, it is definitely MXR , not Dunlop. Probably some of the last ones. They were moving toward the newer circuit (as with FP's 3-TL072's).

I'll keep plugging away at this thing, although I'm still not sure what to look for with a scope, if it comes down to that..