70's mxr phase 90 help needed!

[jackostrato]

hi guys

i hope this is the right forum for this:

i installed a  dc jack on my old, 74ish, script logo phase 90. i seem to have done something wrong and the thing now sounds like a vibrato pedal. i.e.-i'm only hearing the modulated signal without the direct signal, hence no phase. my phase 90 already had true bypass (dpdt switch) and i've drilled a hole and installed a 3 dc plug like this http://www.smallbearelec.com/Detail.bok?no=93.

i returned the wiring to stock (with the bypass mod) but it hasn't fixed the problem. does anyone have any idea what might be wrong?

btw, please give me the dumb guy explanation/wiring drawing (no schematics please), i'm a guitarist y'know.

thanks!

[MikeH]

Is it full of that nasty foam inside?  Sometimes old MXR pedals have this foam to insulate the board from the enclosure, and the foam breaks down over time.  And getting in there and messing around can cause the foam to crumble.  When this happens the pcb makes contact with the enclosure and grounds it out, causing the effect not to work properly.

If it has crumbly foam try insulating if with a piece of cardboard or something instead.

[hackertronix]

yeah, that foam disentigrates...i ran into this with a 70-something phase 90 too. i tried everything, cleaning with air, contact cleaner, still would not work right. it sounds more like a thin distortion now.

[jackostrato]

no, it's clean inside. matter of fact it was working fine before i did htis so i mustive done something. just wondering if anyone's got an idea of a component or connection to troubleshoot before i spend even more money on it and send it to a tech.

[Govmnt_Lacky]

no, it's clean inside. matter of fact it was working fine before i did htis so i mustive done something. just wondering if anyone's got an idea of a component or connection to troubleshoot before i spend even more money on it and send it to a tech.

Here is a fantastic place to start:

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

You can find a schematic of the circuit here:

http://www.tonepad.com/getFile.asp?id=42

Now.... this is not an EXACT copy of the schematic or layout however, it should get you going to troubleshoot. It may take some interpretation on your part but, that is why it is DIY 

Post back with the info from the first link and you will SURELY get more help.

Good Luck 

[jackostrato]

well, i appreciate it but this is over my head. i was hoping for someone to say "check this or that connection" or "test such and such component with a multimeter". maybe back to the tech

[Govmnt_Lacky]

Truthfully.... it is not over your head. It just takes a few minutes to do some simple research about what the parts are, how they operate, and how they are connected and you are off and running. This is a DIY site and there are a lot of people that are here willing to help you along but, it is not a free repair site. 

Not trying to be ugly about it because, lord knows that I have posted numerous help topics however, the forumites are fickle and need reassurance that you know what you are talking about and are capable of attempting a repair. No one wants their time wasted.

You would be amazed at what you can accomplish when fixing these circuits and how simple it can be when you study and learn about them. 

I hope you try but if not..... Good Luck 

[hackertronix]

per "the schematic", it is a question of "which" schematic?! there were several circuit changes to the p90.

it's hard to do the R28 mod when the components are not labeled on the pcb...i think that mod is for newer model pedals anyhow.