Author Topic: MXR Phase 90 eVh  (Read 319 times)

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Craig1969

MXR Phase 90 eVh
« on: December 01, 2017, 10:37:01 AM »
Hi I have a broken phase 90 EVH  I have replaced the diodes that may have been blown when the pedal first went kaput if the battery was connected and the pedal was switched on the blue led would light-up
Now when the pedal is connected to the battery and engaged the LED does not light-up until a guitar cable is put into the input
so that is something that has changed
I am very new to electronics and am only trying it out after i acheived remission from Multiple Myeloma it has taken my mobility so everything i do has to be seated so after a 13year break i am back playing guitar
i have a multimeter it is only a cheap one not sure if its adequate
can anyone help me to check Voltages Continuity etc of the things i need to check and a little guidence on the multimeter settings would be fantastic too
i have tried to do a continuity test as i said i am really in the dark with it but i got some readings if they can help me explain

CR1 - 0.83  11.6
CR2  13.2    14.8
SW2 16.6 16.6 16.6 16.6 0 0
J3 18 18 18
R1 139

the multimeter gave me different readings depending on which side was red or black on the CR1&2

I tried with the battery on not sure again if it is correct CR-1 15.9   CR2 16.5


any info would be very welcome
I will add some pictures of multimeter and board from my mobile






« Last Edit: December 01, 2017, 10:44:51 AM by Craig1969 »

thermionix

Re: MXR Phase 90 eVh
« Reply #1 on: December 01, 2017, 03:45:11 PM »
Now when the pedal is connected to the battery and engaged the LED does not light-up until a guitar cable is put into the input

That is normal.  The battery is disconnected when the input is unplugged so that it doesn't drain when the pedal is not being used.

Most (not all) modern pedals will turn on with nothing plugged into the input if an external power power supply (wall wart) is being used, because battery drain isn't a concern.

Craig1969

Re: MXR Phase 90 eVh
« Reply #2 on: December 02, 2017, 04:07:11 AM »
Thank you for the reply is there anything else you could shed any light on in this instance
The pedal used to light the LED with no guitar inputs at all on battery power

Slowpoke101

Re: MXR Phase 90 eVh
« Reply #3 on: December 02, 2017, 05:08:48 AM »
I don't know if this will help at all but from your picture of the component side you appear to have a broken PCB track going to the cathode (banded end) of CR2. The soldering on CR1 could be a little better too. Check the tracks going to both diodes to make sure that there is no other damage.
The won't turn on without an input lead plugged in is the usual behaviour for battery powered pedals. Saves battery drain when not being used - assuming that you unplug it. However in your case you will find that the input (and I suspect the output socket) has been modified to prevent this action. The ring contact (tip, ring, sleeve) has been modified so that the moving contact is supposedly permanently connected to the moving contact (or trying to be). It has been pulled up and out of its normal position and bent up and over to contact the moving portion. Why? No idea. Not a reliable mod anyway as it appears not to be working now.
Good luck with the repair.

After having had a look at some other "gut-shot" pictures of these phasers I can now see the reason for the input socket mod. The moving contact should make contact with the "bent up and over" contact when a plug is inserted. No doubt it has been arranged this way so that if a stereo plug was inserted and the plug's ring connection was not connected to the sleeve connection (ground) the effect could still turn on. If the socket was arranged "normally" the circuit would not be complete and the effect would not turn on. But in your case since the effect could be turned on without an input plug being inserted the "bent up and over" contact was probably bent further down to make a permanent connection to the moving contact.
« Last Edit: December 02, 2017, 05:49:29 AM by Slowpoke101 »

Craig1969

Re: MXR Phase 90 eVh
« Reply #4 on: December 05, 2017, 07:16:17 AM »
I have included a picture of my attempt to clean up the rail around CR2 I am unsure if I have for any good or not there is a before and after and the settings for my multimeter no battery attached and the reading rose up to over 20 on both diodes






antonis

Re: MXR Phase 90 eVh
« Reply #5 on: December 05, 2017, 07:29:52 AM »
Maybe, you over heated your diodes..
(especially CR2..)

Your multimeter has a "diode check" selection (just left before 10A range) so check your diodes..
(with red lead to red body side and black lead to black rim you have to read 500-600mV voltage drop and nothing on the oposite arrangement..)
Tired of updating my account to enable 3rd party hosting..

Craig1969

Re: MXR Phase 90 eVh
« Reply #6 on: December 05, 2017, 10:18:58 AM »
Hi Thank you for the reply
I made the check on CR1 & CR2
CR1-002
CR2-002

Reversed CR-1 002
             CR-2 002

If i kept the tester on the would both increase slowly 1 point each to aroun 020

antonis

Re: MXR Phase 90 eVh
« Reply #7 on: December 05, 2017, 10:28:39 AM »
Sorry Graig but without units and decimal points on your measurements it's hard to understand what's happening..  :icon_wink:


P.S.
It seems to me there is a capasitor wired across diodes (increasing measurement..) but without a diagram it's hard to say..
« Last Edit: December 05, 2017, 10:34:07 AM by antonis »
Tired of updating my account to enable 3rd party hosting..

Craig1969

Re: MXR Phase 90 eVh
« Reply #8 on: December 05, 2017, 10:41:26 AM »
Ok no problem but that setting on my meter just shows 1 when nothing is attached or just 3 digits no points