MXR Phase 90 Speed Problem

[Luqqas]

Hello everybody.

I have the stock Phase 90. 2 Years at least in my power.

The problem is that somehow when I put the "Speed" knob at  25% it doesn't work. Then put it at 30-35% neither works. Close to the half it starts to work.

Can't get slow speed on the phase effect.

I opened and check to potentiometer be a  "reverse log" and not another one. I know that on DIY Phase 90 when you don't use an reverse log, you get this kind of response on the cloclwise trail (using a log or linear pot).

What can be?

[Luqqas]

I'll try to clean the pot and then I'll be back a post my results

Greetings

[Mark Hammer]

Good strategy.  Remember that higher resistance = slower speed.  And you can't get resistance much higher than open circuit when the wiper is not making contact!   

[Luqqas]

Well, I've cleaned with a proper product (contact cleaner) and still the same.

Check the solderings points of potentiometer on pcb. Look pretty solid.

Also made an general inspection of components on pcb and specially of resistors an caps directly related with pot.

Effect works great near half of pot. Before that, from 0 to 40% I get the clean sound of guitar and suddenly (around 40% of pot trail) start to hear the phase correctly.

It's funny, 'cause the pot it works as variable resistor (lugs 1 and 2 connected).

Ideas?

[Mark Hammer]

Consider  setting the speed moderately slow, and playing with the trimpot until you hear phasing.  It can happen that when the trimpot is set wrong, you can hear faster speeds but there is not enough sweep to make low speeds audible.

[Luqqas]

Thanks Mark.

I'll do that for sure. And of course, coming back and report results.

Greetings

[Luqqas]

After a try with the trimpot, same results.

The oscillation only starts close to the half on pot's trail.

Could be the pot?

[Fender3D]

Could be the pot?

That should have been the first thing to check 

[Govmnt_Lacky]

Something tipped me off upon reading your initial post again.

You may want to double check which pot lugs are connected. According to some other layouts I have seen for the Phase 90, it should be lugs 2 & 3 that are connected. NOT 1 & 2.

When looking at the BACK of the 500K Rev Log pot with the lugs pointed down, you should have wires/connections on the MIDDLE lug and LEFT lug.

[Mark Hammer]

Use of 1 + 2, rather than 2 + 3, won't make a difference in whether it works, merely HOW it works.  In the circuit, speed will increase as pot resistance decreases.  Wiring up the pot opposite will make the resistance increase as you rotate clockwise, such that fastest speed will be at 7:00.  If all you have available is a regyular 500k log pot, that may well be the best way to wire it up.

I will say that one cannot expect too much out of inexpensive pots.  I have, on occasion had pots that misbehaved and refused to make proper contact in part of their range.  These days, I generally pop the back off of new pots, to have better access, and give the rivets holding the solder lugs a gentle squeeze with my needle-nose pliers, just for extra insurance.  It's overkill, I know, but it comes from havng pots misbehave in past, and that was what cured them.

[Fender3D]

Sorry mates, I don't wanna be mean or what, but...
4 days and 10 posts later, luqqas hasn't swapped his pot yet...

[Luqqas]

Sorry mates, I don't wanna be mean or what, but...
4 days and 10 posts later, luqqas hasn't swapped his pot yet...

It's ok Fender3D.

The fact it's that I don't have a 500K C pot in my hands at this moment. I have a lot of other values and types. But not C -wich by the way are pretty much uncommon-. And the exact replace for this phaser is 470K C.
Pretty unconfortable, because I don't know if a provider had these ones.

Also, this Phaser it's not mine. It belongs to the other guy who plays guitar with me. And I don't wanna mess up.

I'll change for a 500K C and report results.

Greetings

[Luqqas]

Something tipped me off upon reading your initial post again.

You may want to double check which pot lugs are connected. According to some other layouts I have seen for the Phase 90, it should be lugs 2 & 3 that are connected. NOT 1 & 2.

When looking at the BACK of the 500K Rev Log pot with the lugs pointed down, you should have wires/connections on the MIDDLE lug and LEFT lug.

Understand your point. So, went for the effect and take some  pics.

And check out how on the front of pcb, lugs 1 & 2 are connected. On the back of pcb,  terminals 1, 2  & 3 don't have contact.

(click on pics to view a little better)

[Fender3D]

I read you messed with trimmer... I just hope you can set it back again default...
Being too much technical here may lead to dangerous tips...  
For a faulty pot, there may be a lot of reasons (includung global warming and mayan...   ),
but first things first... swapping the pot with another (you may use any value 1M-100k just to check) it's easier and safer

[Govmnt_Lacky]

And check out how on the front of pcb, lugs 1 & 2 are connected. On the back of pcb,  terminals 1, 2  & 3 don't have contact.

Lugs 1 & 2 being connected is OK. That is common practice in case something happens to the pot ( i.e. if it shorts internally)

On the solder side of the board, it also looks like lugs 1 & 2 are tied together (this is OK) and Lug 3 is connected to a trace (this is OK as well)

You can always download a schematic of the Phase 90 and use a DMM to ensure that the pot lugs are contacting their appropriate components.

[Luqqas]

Don't worry for the trimpot. And be as technical as you can be.

Many years on DIY world, many mods and repairing,  lot of forums readings and things attached to.

Sometimes, I like to post things for wich I can't find answers without have to enter with my "knife" on effect guts. With an stock MXR never had have this pot issue. And I though to share it with this gorgeus comunity.

swapping the pot with another (you may use any value 1M-100k just to check) it's easier and safier

If the pot it's not a Rev. Log., the response on the trail will not be appropiate and may induce to more confusion.

And check out how on the front of pcb, lugs 1 & 2 are connected. On the back of pcb,  terminals 1, 2  & 3 don't have contact.

Lugs 1 & 2 being connected is OK. That is common practice in case something happens to the pot ( i.e. if it shorts internally)

On the solder side of the board, it also looks like lugs 1 & 2 are tied together (this is OK) and Lug 3 is connected to a trace (this is OK as well)

You can always download a schematic of the Phase 90 and use a DMM to ensure that the pot lugs are contacting their appropriate components.

Already did that. The DMM shows everything ok. Everything points to the pot.