Electro Harmonix POG - Switch question (Rev. A)

[aavatech1]

Greetings, I'm trying to resurrect a Rev. A POG that has seen better days for sure and so far all is going OK.
But, I'm going batty trying to figure out what the deal is with the LPF mode switch!
This is a "three position" switch judging from the screen print on the case but I just can't seem to find it on the schematic.
There are references to what looks like two (2) "3 pos." switches on page 5 of the schematic that I've posted.
These switches are not marked on the schematic as "OMIT from production" as much of the circuitry on the schematic is. And to me it looks like "S2 / S3 / S4 / S5" are actually DPDT slide switches. There is only one 3 position slide switch on my version POG. My POG doesn't have the "Misc. 1 / Misc. 2" or the "Preset 1. / Preset 2." switches either. None of which are likewise isolated on the schematic as "OMIT from production"!
So I'm doing a real head scratcher with this one. And I was hoping that a fresh set of eyes might be able to help clear this up. I can't find any other 3 position switches on the schematic but everything else I need seems to be there.
My board says "Rev.A" like the schematic and there are unused portions of the board that correspond with the "OMIT" sections of the schematic. So I'm pretty sure I've got the right schematic.
Any assistance would be greatly appreciated.
**Note: I hope it's OK to post these schematics. I tried to find info about what's OK to post and what might not be but couldn't find anything while searching. If it's not cool I'll take them down and supply to anyone that requires them.
Thanks**
Mark->

[Blackaddr]

It looks like the Filter Mode Switch is supposed to be wired to the 3-position switch S3 (laballed N-O-P) on the schematic. This can be seen by looking at the photo of a working unit as you can see exactly how the switch is wired to the PCB.

[aavatech1]

Oh man, I love you! Thank you so much. I didn't hope to think that someone might have a picture of the guts of one of these or pop theirs open to take a look. At first it looked like the green wire is going to somewhere other than "P" in the image you posted but I think that the green wire must have just broken from the "P" contact.
But I'm still kind of confused about the switch itself. The schematic shows a DPDT, two position switch. And that makes sense from the schematic standpoint, one position connecting "N" (+3.3V) to ground through the 150 ohm resistor and the other position connecting "P" (+3.3V) to ground through a 150 ohm resistor. There are obviously all kinds of three position switches out there but what kind would work here and HOW would it work here?! If the three positions of the switch are supposed to create a P0.2/AD2 to ground and a P0.3/AD3 to ground condition what would the third condition, i.e. position, create? Would this be a simple on-off-on switch? All input is appreciated, and thanks agian,
Mark

[Blackaddr]

It's a simple DPDT switch, though it's only using one side effectively as a SPDT switch. The circuit is using N and P to detect the position of the switch. In one position, N is disconnected and is pulled HIGH, while P is grounded LOW. The other switch position is the opposite.

Logically, the state of the switch has been encoded redundantly into two bits of information when only one should have been necessary. There are a couple possible explanations for this.

Maybe they wanted redundancy or the ability to detect a miswired switch manufacturing fault?

Maybe for efficiency reasons on the 8051 it was necessary that each switch position be encoded to a HIGH voltage somehow? Maybe they need to use rising edge interrupts? Who knows. It's all speculation.

In summary, the circuit is very weird and appears unnecessarily complicated by modern standards. In either case, it is what it is, and you need a SPDT switch (or DPDT with one side unconnected) to operate the circuit correctly.

[aavatech1]

Thanks "Blackaddr" for the additional info. This schematic was so not making sense for me.
So, in essence, regardless of the silk screening on the top of the unit that says " LPF Modes (1,2,3) it is only a
two position switch, and not a three position switch. Just like it shows on the schematic.
I'm assuming that the 3 LPF mode numbers on the unit make as little sense to you as they do for me?
(..I'm sure hoping so)
Thanks again,
M
 

[Blackaddr]

Thanks "Blackaddr" for the additional info. This schematic was so not making sense for me.
So, in essence, regardless of the silk screening on the top of the unit that says " LPF Modes (1,2,3) it is only a
two position switch, and not a three position switch. Just like it shows on the schematic.
I'm assuming that the 3 LPF mode numbers on the unit make as little sense to you as they do for me?
(..I'm sure hoping so)
Thanks again,
M

No, I think you're right. I think I glossed over that you mentioned "3 position" before and just assumed 2 position after looking at the schematic circuitry. That explains the circuit topology, it all makes sense now. If it's a 3 position switch where the middle has both throws open, then the P and N would both be pulled high.

Example:
POS1 -> P high, N low
POS2 -> P high, N high
POS3 -> P low, N high

That means you need to find a 3 position SPDT or DPDT slide switch. You might be able to get away with a normal 2 position if you don't care about losing the filter selected by the middle position, or the switch might do it for you anyway, but there will be no detent in to keep it firmly in that spot.

[aavatech1]

Well, I put the two position DPDT switch in, wired it up and IT'S ALIVE! After I don't even know how many years it still lives! Can I get an Amen, Brothers and Sisters?! What's weird is that when I put the two position switch in it seems like there's only enough room in the cut out for a two position switch. Unless the three pos. switch's "handle" travel is super tiny. I'll give it the once over tomorrow and report my findings with the LPF mode switch. The rest of it seems to be working fine and sounding great. I'm psyched! This thing is wicked. LPF switch aside, I have to replace several of the faders in this guy since the fader handles on 5 of the 8 faders are snapped off! (..I didn't do it!) I've run the part numbers on the faders but have got bupkis so far. Replacing faders is rough. I'm rerely able to find replacements that fit old audio gear. I've got a Sony MX-20 mixer in great shape with one fade toast and I've been looking for a fit for a couple years now. Might be time to kluge!
More to follow...
Thanks again,
M

[aavatech1]

A quick update on the POG restoration. I located all of the slide potentiometers needed to replace the broken ones on my POG. They came from Small Bear Electronics. The folks were great and very helpful.
When they arrive I'll post the install and results. Thanks again to Blackaddr for the kind help with this unit.
M

[Blackaddr]

No problem! I gotta help out a fellow POGer! The nanoPOG is the heart of my live rig.

[aavatech1]

I'm totally salivating waiting for these pots. My first audio test was enlightening to the capabilities of the POG!
The first thing I played was "Hope you're feeling better" by Santana! The beginning is actually a Hammond B3 but
the POG does it nicely!
More to follow...

[aavatech1]

Well, the slide faders have come in. They went in without a hitch and she's back together again! 
It sounds fantastic and I'm in the debt of "Blackaddr" for the kind assistance offered.
I'm currently in the process of turning a vintage tube record player into a small guitar amp but stomp box
building is in my immediate future as well. Therefore I shall return, as was once said.
Thanks again,
M