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Help on a Failing Script MXR Phase 90

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12/6/1999 8:18 PM

Help on a Failing Script MXR Phase 90

I have an old script logo Phase 90 that sounds awesome when it works. Lately it works fine when I first plug it in and for the first couple times I step on it, but at some point in the night something happens cause when I step on it there is nothing but a barely audible effected sound coming out. Step on it again and the clean sound is fine but the effected sound is little or nothing for the rest of the night.

Of course when I get home and try it it works fine but at gigs and practices when it is plugged in for a while at some point the effect breaks down. Everything looks fine inside visually.

The jacks are fine and clean with no pops or noise from plug movement. It doesn't seem like a switch problem to me.

Any ideas or similar experiences out there?

Thanks,
Tim P.

12/6/1999 8:46 PM

Pedals from this age are prone to two general maladies - poor soldering and aging electrolytic caps.

If it were mine, I would first remelt every solder joint on the bottom of the board, touching each joint with just a tad of fresh rosin core solder. If that didn't fix it, I would replace every electrolytic capacitor in it.

It's possible that it's not one of those two, but those are very frequent.

12/7/1999 4:55 PM
CJ Landry	Just a note, I have seen some of the script logo versions come in with the 10uf tantalum cap in the LFO circuit put in backward. THis had to be do ne by someone other than the factory because it will not work with this cap in backward. It might not be a bad idea to check for this also. CJ

12/8/1999 1:33 AM
Ed Rembold	R.G. All 6 script P90's I've seen did not have a single AL electro, all ceramic and a couple Tant. not much help, I know. I had one which had foam, that isolates the PCB, that the owner replaced himself, which was conductive. make sure the PCB is not floating around! Ed R.

12/18/1999 4:50 PM
BIG Dave	Is the battery failing?

12/21/1999 1:41 AM
Rick	I have exactly the same problem with a 3ms phaser that I built a couple of months ago. It works fine when it's first turned on, then the phasing gradually fades out. Shorting the battery temporarily brings the phasing back. Come to think of it, I also have an EH Echo Flanger that does the same thing. I hope someone has a solution for this, it might help me fix two pedals.

12/21/1999 6:01 PM

Let's think about this for a moment. The only thing that would cause the phasing to gradually fade out is that the LFO is stopping or the bias voltage on the JFETs is getting outside the proper range for them to phase, and this is a gradual effect. That says that there is a capacitor somewhere that's either charging up or discharging to give you the fade-out effect over time. Since it's repeatable, and happens over again if you short the power supply, it's probably the bias voltage of the JFETs. Just off-hand, I'd say that the bias zener being dead is the most likely problem, the next is some biasing problem with the LFO.

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