Re: Effects Loop Switches

[Dante]

I split this discussion off from the "my MP-2 has a hiss in channel B" thread.....I have a problem with the Effects loop switches in my MP-2. 

Does this look like the right replacement switch to you?


https://www.digikey.com/en/products/detail/e-switch/PBH2UOANAGX/805270

[Dante]

I took the two switches out, just need to replace them. I have never taken off the bottom cover (that I know of). It was covered in sticky goo. I figured out it was the rubber feet that are inside, two of them had actually melted.

We are in a hot area, I have played outdoors in 105°F weather (usually with a fan on the rack, but it can sit in the car for awhile)

Here are some pix of what I found, a shot of the points I had to desolder (highlighted in yellow) and I will also attach pix of the switches I took out

[Dante]

EDIT: before I took out the switches, I cleaned them and tried them again. While the ChA switch was now stable, it was much lower volume than ChB, which was still unstable....but way loud. I thought that was pretty odd, and figured both needed to be replaced....so I took them out

Pix of the switch

[rnolan]

Hey Dante, Wow, it must have got really hot to melt the rubber thingys like that.  Albeit MP-2 do get really hot.  I have to wonder what mine look like.  I have had the bottom off a couple, but not all.

The switches look like the real deal .  Has it helped with the hiss??

[Dante]

I saw two switches that are very similar on that website linked above, just want someone to chime in and tell me which one I should use to replace the ones I took out

Here's one of them
https://www.digikey.com/en/products/detail/e-switch/PBH2UEENAGX/805271

Here's the one I listed above
https://www.digikey.com/en/products/detail/e-switch/PBH2UOANAGX/805270

Looks like Mouser has one too
https://mou.sr/4dJamxV

[Harley Hexxe]

I'm afraid I can't be much help with this one, this would be MJMP's wheelhouse.

[Dante]

UPDATE: The mouser switch I referenced earlier is NOT the right one....I'm searching for the correct size. See the pix below, for the one I took out and the one from Mouser

[Dante]

I found a couple that appear to be the right size pins, do I want Shorting or Non Shorting on my latching switch?
Here's what I found:

https://mou.sr/4cW0QGn

https://mou.sr/4cW0QGn

You cannot view this attachment.

[Dante]

Just in case those switches are also wrong, I disassembled both my existing switches and took an emery board (aka a nail file) to every contact inside. 

They're all bare metal now, hopefully that'll work

I managed to reassemble the switches after cleaning. My mechanic skills helped that process.....taking things apart is my specialty, putting them back together is the challenge 

[Harley Hexxe]

Dante,

I can't say if the switches are right or wrong, but I do know that when it comes to cleaning contact surfaces, I would never use anything more abrasive than a pencil eraser.

[rnolan]

Hey Dante, I agree with Harley, I've occasionally used 1200 to clean jack socket contacts but that's even probably too course (scotch bright is probably better or maybe 0000 steel wool?).  These things tend to be iron/steel (or similar??) with a coating of nickel or gold etc. If you scrub/file them to hard it takes off the coating and then they tarnish again quickly (rust) and don't contact as well.

You should be able to check if they are working with your multi meter.  As they are a 2 position switch (in/out) I suspect it is "similar " to a PU 2 way switch ?.

So I checked the schematic, basically a 6 pin switch:
3 2 1
6 5 4

So out:
3 2-1 Check 1 connects to 2 (only)
6 5-4 Check 4 connects to 5 (only)

In:
3-2 1 Check 2 connects to 3 (only)
6-5 4 Check 5 connects to 6 (only)

If so it's working 

[Dante]

As usual, I repair things with the finesse of a gorilla - contacts are bare metal, YEAH! I have nothing to lose, the switches are fubar anyway, so EFF it.

I checked the contacts with my multimeter and both switches are behaving as Richard states above. I expected the switches to join contacts across the switch, but that's not what I found inside and with the multimeter. The little metal piece inside joins posts that are next to each other. (I pulled one of the switches apart to get a pic of that piece - see below)

Those little metal pieces with springs behind them are what make the contacts with the pins running through the switch

[Harley Hexxe]

So basically, the center pins are in contact with the push-button switch at all times. With the switch depressed, the center pins are connected to the two pins at the rear. When the switch is out, the center pins are connected to the two pins at the front.

If I had to guess Dante, I'd say this is a non-shorting switch. It seems to be physically changing the path that is fed into it through the center pins. If there is a short happening, then it would be outside of the switch itself. I'm only guessing at this so take it with a grain of salt.

[Harley Hexxe]

Richard,

I wouldn't use steel wool either. It leaves behind very fine strands of the wool that could cause an unwanted short circuit. It's very hard to get out of a circuit like this too because it can stick to something like flux residue and can be very hard to spot.

[Dante]

@Harley: Yes. That's exactly how it works

I totally agree, I ordered the non-shorting switches a couple days ago, they'll be here in a few more days - Thank you for confirming (or at least complying with) my suspicions.

@Richard: Thanks for mapping that out, I was just wrapping my tiny braincell around the switch operation when you posted that. At first, it didn't make sense (I thought the switch was supposed to make contacts across the sides, rather than on each side - not sure why I thought that).

The multimeter test sealed it for me, the ones I butchered are working fine (but I haven't tried wiggling them to see if they cut out like before). If the new switches are wrong, I have no reservations trying the ones I sanded down, they seem so clean and fresh now ;)