Mxr phase 90 tech question

Discussion in 'Amp Tech Center' started by Martyepisg, Jul 27, 2020.

  1. Martyepisg

    Martyepisg TDPRI Member

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    Hello forum,
    I hope this is the right spot for tech questions on pedals.
    I have a mxr phase 90. It is not working at all with 9v battery (no power/led light) when engaged. When plugged into AC power the led light comes on when engaged but no sound comes through to the amp.
    I am hoping someone can help me trouble shoot or has an idea what a fix maybe.
    I appreciate your response in advance.
     
    Last edited: Jul 28, 2020
  2. tubejockey

    tubejockey Tele-Holic

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    What is the voltage and current rating on your power supply? Sounds like it might not be enough. Is it a regulated supply or not?

    ##Edit## I think I misread your original post. Do you get sound through when in bypass? Any noise at all? How old is the unit? Does the footswitch need cleaning?
     
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  3. Martyepisg

    Martyepisg TDPRI Member

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    Thanks tube jockey,

    The power adapter (that I scrounged) says
    Input: 100-240v
    50/60 Hz 0.5A
    Output .5v -100mA

    when in bypass (button not engaged and led light off) sound goes through from guitar out amp. When button pressed down led light goes on but no sound at all goes from guitar to amp.
     
  4. brokenbones

    brokenbones Tele-Holic

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    The switch could be defective or you have a loose signal + input wire from the switch to the pcb.
     
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  5. tubejockey

    tubejockey Tele-Holic

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    Look for a 9V regulated adaptor. Make sure it has the correct polarity for your pedal, anything rated for 50mA or more will work fine.
     
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  6. Martyepisg

    Martyepisg TDPRI Member

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    Thanks broken bones. Do you have a suggestion to trouble shoot to determine if this is the problem?
     
  7. brokenbones

    brokenbones Tele-Holic

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    Have you taken the thing apart to inspect the PCB? I would advise doing this first to see if there are any burnt components or traces. Do you have a multimeter? Soldering iron? Reading back through your post and having a look at mine, my guess is either a diode or op-amp have gone bad. Let me know if you see anything out of the ordinary. How old is the pedal?
     
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  8. Martyepisg

    Martyepisg TDPRI Member

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    Thanks broken bones, I have the needed tools. I did take out the pcb and from my very untrained eye there was nothin burned out. I will have a closer look under better light tomorrow.
    Appreciate the advice.
     
  9. Martyepisg

    Martyepisg TDPRI Member

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    thanks tube jockey, I got the correct power adapter (bought new to assure compatability) and I changed out the 9 volt clip. So the positive news is that the led lights up when I have only a 9v battery installed and when I have the ac/dc power adapter plugged in.
    The bad news is that once the button is pushed down no sound travels from guitar to amp. When not pushed down the sound travels through in bypass no problem. I opened up the pcb and eyeballed it again and can’t see that anything is burned out.
    Do you (or anyone) have advice about how to trouble shoot or what it may be?
     
  10. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    Which version of the MXR p 90 do you have?
    Is it the tiny SMD board?
    Is it the 6 op amp?
    Is it the 3 op amp?

    Show us pictures.

    Most of the time it is something simple. Look for bad solder joints especially on any wires to or from the board. All of the joints of the moving parts (pot, switch, plug in, etc.) are suspect.

    The board can also ground out. Look for anywhere it may touch the chassis. If you can try to make it function out of the box, do so.

    Work the switch several times. Likewise work the pot back and forth.

    Do you have a multi-meter to check voltages etc?
     
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  11. Martyepisg

    Martyepisg TDPRI Member

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    thanks left coast,
    It is the m101. I took the pcb out and don’t see anything obvious, I didn’t try looking for anything loose yet. Here are a couple of pics of the board. I do have a multimeter. I am no pro, can you advise on what I should test?
    62CFB107-64E4-4EBC-8C7C-847A5800E101.jpeg 929A653A-8560-4050-B359-606E677E7841.jpeg 0729A3F3-E3C9-443C-8D1E-0A563DA36EBF.jpeg F3C93857-76C8-412A-909B-427E33E33399.jpeg 9B4D66AC-1BD8-4915-AADC-F48036010DF7.jpeg
     
  12. monkeybanana

    monkeybanana Tele-Meister

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    mmhmm
    I bought a fuzz pedal from the ‘90s that would cut out. I noticed moving
    The wires would cause a connection to lose contact. I sprayed DeOxit on the switch and it cured it. Could be something like that.
    Try lightly pushing things around when it’s on.

    Another example: I was reading about the trim pot on the Phase 45 and someone wrote their pot had to be resoldered because it was cutting out.

    Hopefully it’s that simple. Good luck.
     
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  13. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    I don't find a schematic for this particular layout.
    I see switches on the i/o jacks. I am not sure they do anything but make sure they are making good contact in case they do. Clean them.

    With the unit *on* and effect engaged.
    Check the voltage on the op amps pin 4 to pin 8.
    Check the voltage on each terminal of the trim pot. (Clip the neg probe to the jack sleeve terminal or find another ground.) It should have voltage on two of the terminals and 0v on the other.

    I read another P90 had a shorted cap. (C10). Check the cap can(s). I only see one on the board. Schematics for other P90s show 2 cans. C8 and C10.

    I am assuming you do not know the history of this P90 to know whether it was given too much (or reverse) voltage before it died.
     
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  14. nathan5782

    nathan5782 Tele-Meister

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    I did some troubleshooting on one with the same circuit board last year I’ll see if I can still find my notes/diagram. If you have an audio probe or build one then you can use a looper pedal to play a repeating part and listen to the components to see where the signal dies.
     
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  15. Martyepisg

    Martyepisg TDPRI Member

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    Thank you all for jumping in with advice, it is very appreciated.
    Nathan any notes or diagrams you can share I’d be very obliged to see. Thank you in advance.
     
  16. nathan5782

    nathan5782 Tele-Meister

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    The phase 90 I was working on had a weak phase sound. There was an old thread on here that was helpful, I might have the page saved on my work computer I can check tomorrow, I also found a schematic that is the closest match that I printed out it was made by somebody named Nero F. Rox that included some mods. Here are voltages for the 8 pin chip TL062CP:
    1. 4.40
    2. 4.89
    3. 2.41
    4. 0.0
    5. 5.24
    6. 5.41
    7. 8.82
    8. 9.43
    Here are the voltages for the larger chip under the speed pot TL064CN:
    1. 4.85
    2. 4.88
    3. 4.87
    4. 0.0
    5. 4.88
    6. 4.85
    7. 4.93
    8. 4.88
    9. 4.89
    10. 4.93
    11. 9.44
    12. 4.88
    13. 4.89
    14. 4.93
    I also have voltages for the JFET transistors (2N5952), the middle leg is 4.40, one of the outer legs should get about 4.36 and the other outer leg about 1.13-1.25. I'll see if I can dig up the schematic tomorrow or I can make a scan of the one I printed out.
     
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  17. nathan5782

    nathan5782 Tele-Meister

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    Here's the old Phase 90 troubleshooting thread dated from 2009-2018.

    https://www.tdpri.com/threads/mxr-phase-90-not-working.176979/

    I have a schematic that was the closest match to the block logo Phase 90 I could find when I was working on it last year, I don't know if there would be copyright issues, the URL on the schematic doesn't work anymore and I can't find the other effect pedal website where I got this from to link that page, I think the resistor cut off on the top is R28. U1a and U1b are the TL062CP chip and U2a-U2d are the 14 pin TL064CN chip.
    I also have a drawing I did myself where I was signal tracing and mapping the circuit board components but never finished.
     

    Attached Files:

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  18. Martyepisg

    Martyepisg TDPRI Member

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    Thanks very much nathan you gave me a lot to work with!
     
  19. Martyepisg

    Martyepisg TDPRI Member

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    Based on the old thread
    I read through the old thread (thank you fro sending it), and what appeared to work for the OP was clipping off the diode that was identified as (1n914 or 1n4148) it is the second diode above the 9 volt clip. this unfortunately had no effect for me, and the issue persists: led lights up but no sound comes through.
    I am hoping you might have suggestion about what further up the signla chain might be going on. I appreciate any advice.
     
  20. Martyepisg

    Martyepisg TDPRI Member

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    I found a similar thread on a les paul forum. same issue and a tech took the mxr in and indicated that 3 components were fried.
    the reverse polarity diode and op amp IC TL062 and TL064. some google search showed me what these pieces are. i am going to try replacing all and see what happens.
    If anyone has other advisement I would appreciate it, thanks again!
    here is the thread I saw:
    https://www.mylespaul.com/threads/help-me-revive-my-phase-90-pcb-pics-inside.297676/page-2
     
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