80’s MXR Commande Phaser M-161 Troubleshoot Help?

[Psychophonic]

I have a deranged Commande series Phaser. I am still learning how to read and understand schematics. This phaser’s rate ranges from super fast to even faster. It’s unusable, in terms of a “normal” phaser.

This guy’s Commande Phaser is doing the same thing:
https://youtu.be/PysjxeXbeJs

By comparison, this one seems to work properly:
https://youtu.be/7SVUkyWZ2SA

Has anyone experienced this issue? Any troubleshooting advice?

[Mark Hammer]

That unit uses a "switched resistor" strategy for producing sweep.  This is the same general strategy that MXR used for the Envelope Filter, and their early Analog Delay.  The 4066 (or possibly 4016) CMOS switches are turned on and off at a high frequency.  How long they remain on vs off  what is called the "duty cycle" - determines the average resistance of the switch+6K2 resistor.  The more time the switch is turned on, as opposed to off, the lower that resistance.  The 4013 flip-flop chip is used, in conjunction with the adjunct components, to turn the 4066/4016 switch on and off, in a manner corresponding to what the LFO is telling it.

Since CMOS chips like the 4013 and 4066/4016 are susceptible to damage from static and supply voltages over 15V, the first strategy to begin with is to simply install new chips for old.  If you ARE getting something that sort of sounds like phasing, I'd begin with the 4013.  For a pedal of this age, it is also a possibility that one or more electrolytic caps are past their best-before date.  Looking at the sweep-generator circuit, there appears to be only one cap that might be problematic - a 22uf unit.  Insomuch as desoldering a 14-pin CMOS chip can be a pain, begin with that cap, and if replacing it doesn't yield decent sweep, THEN consider the 4013.

[Psychophonic]

Great read, thank you. So start by replacing the 4013 and 4016 chips? I see one of each on this pcb. Replace with exact part numbers?

Edit. Ok I will replace that cap first.

[Mark Hammer]

Yes.  The letters before and after the 4016/4013 may be different but the part will function identically (i.e., it doesn't need to say "CD4016BE", specifically, to be a 4016).  Sadly, the existing chips are soldered to the board and not socketted.  That's why I suggested replacing the 22uf cap (the yellow one) first.  There is an off-chance it is messing up the sweep rates, and it is the easiest thing to desolder and replace.

I will strongly recommend that you purchase some solder wick to do this, rather than attempt it with a solder sucker.  Fresh solder wick works well, but if you have some and it is older and mildly tarnished, I like to dab some flux on it.  I find that "supercharges" the wicking properties, so that the solder is wicked away more easily.

Finally, I will note that MXR used low power TL062 dual op-amps all around.  The one on the left of the pic is used for the LFO and is appropriate.  The three on the right hand side, however, are all in the audio path.  IN noise/hiss comparisons, the TL072 outperforms the TL062.  However, since few of us were using power bricks in the early '80s, and largely relying on batteries, priority was given to lower current draw, rather than lower noise.  The pedal will perform more quietly if those three chips are replaced with the 72 variety.  But once again, desoldering all those chips can risk udamage to the board, so do not attempt replacement unless you find noise is also a major issue....once you've fixed the sweep issue.

[Psychophonic]

Mark, I really appreciate your wisdom and advice. I will proceed per your instructions. The only 22uf cap I can see on this pcb is the larger orange cap located under the left pot. I do have some Panasonic FC 22uf 50v caps on hand.

[Psychophonic]

Update. Mark, you fixed it! I replaced that 22uf cap, tested, and sure enough it sounds like a Phaser now. Mind blown. Sir, you are the man. Thanks so much.

[Mark Hammer]

I wish I was always that good.  But I'm super pleased you only had to replace the one cap and not take on the burden of replacing those CMOS chips

[ElectricDruid]

I wish I was always that good.  But I'm super pleased you only had to replace the one cap and not take on the burden of replacing those CMOS chips

Good call, congratulations!

Isn't it great when it works?!? I love that. Probably because it's so rare!

[Mark Hammer]

Isn't it great when it works?!? I love that. Probably because it's so rare!

Ain't it the truth!

[Psychophonic]

I wish I was always that good.  But I'm super pleased you only had to replace the one cap and not take on the burden of replacing those CMOS chips

Indeed, I was not looking forward to removing those chips. I have desoldering braid but I can never seem to get it to work for me. Still learning.

I have another question for you. Fender Lost Highway Phaser. Liquid (soda?) spilled all over the pcb. When engaged, there is no signal other than what I would describe as pure noise. With all the surface mounted components, at my skill level, is it even worth troubleshooting?



This doesn’t look right either...



Edit. I may have answered my own question, at least to start with. Found this advice:
https://www.premierguitar.com/articles/21973-diy-how-to-repair-a-wet-pedal

[Mark Hammer]

Desoldering braid tarnishes like the leads on any component, impairing it's attractive quality to solder.  So it's a good strategy to keep it in a resealable bag to keep the oxidation to a minimum.  I also find that if I can let a bit of liquid flux soak into it, it really enhances the braid's wicking qualities.  Leaves a bit of a mess after, but it's easier to clean that up than it is to deal with the risk of crack traces or fried components from having applied too much heat for too long.

If you have no luck with your Lost Highway, and are just going to toss it anyway, feel free to send it to me via the cheapest slowest mail route you want. 

Dehydrating methods DO work.  One just has to be patient with them.

[StephenGiles]

Mark, there was a thread on this unit way back on the old Ampage site around 2001-2. The circuit was not clear around the clocking section - there must have been a crease on the schematic from which the scan was done causing confusion. However I think the contributer did get his build to work eventually and the correct connections in the clock established.

I used to print out threads like that, so may still have it.

[Mark Hammer]

I have both the grainy factory schem and what I believe is your redraw of it.

[StephenGiles]

Thanks Mark. that's given me a clue as to where my schematic is!

[duck_arse]

I wish I was always that good.  But I'm super pleased you only had to replace the one cap and not take on the burden of replacing those CMOS chips

Indeed, I was not looking forward to removing those chips. I have desoldering braid but I can never seem to get it to work for me. Still learning.

I have another question for you. Fender Lost Highway Phaser. Liquid (soda?) spilled all over the pcb. When engaged, there is no signal other than what I would describe as pure noise. With all the surface mounted components, at my skill level, is it even worth troubleshooting?


This doesn't look right either...

Edit. I may have answered my own question, at least to start with. Found this advice:
https://www.premierguitar.com/articles/21973-diy-how-to-repair-a-wet-pedal

I repaired a DD10 a few years ago that was had been so full of coke it wouldn't reach the starting line - it was a mess of eaten copper tracks. your board doesn't show the same amount of damage. there is a burn or metal splash on the top left conrner pot - is that showing something has failed?

[Psychophonic]

I wish I was always that good.  But I'm super pleased you only had to replace the one cap and not take on the burden of replacing those CMOS chips

Indeed, I was not looking forward to removing those chips. I have desoldering braid but I can never seem to get it to work for me. Still learning.

I have another question for you. Fender Lost Highway Phaser. Liquid (soda?) spilled all over the pcb. When engaged, there is no signal other than what I would describe as pure noise. With all the surface mounted components, at my skill level, is it even worth troubleshooting?


This doesn't look right either...

Edit. I may have answered my own question, at least to start with. Found this advice:
https://www.premierguitar.com/articles/21973-diy-how-to-repair-a-wet-pedal

I repaired a DD10 a few years ago that was had been so full of coke it wouldn't reach the starting line - it was a mess of eaten copper tracks. your board doesn't show the same amount of damage. there is a burn or metal splash on the top left conrner pot - is that showing something has failed?

That little fleck of solder on the green edge of the pot? Not sure how it got there but it chipped right off with my fingernail. It's gone.

[ElectricDruid]

This doesn't look right either...

I think that looks like a factory fix, unless there's further evidence that someone replaced that pot and broke a track doing it. I've fairly often seen early-version production boards go out with one or two minor fixes like this on them. It's cheaper than slinging the whole batch, even if it is a pain in the neck to do. They'll have used up the stack of boards they had like that, and then fixed it on the next Rev.

[duck_arse]

to me, that ^ looks like a repair, not a mod. looks like a trace lifted, perhaps when the solder was being splashed on the upper pot, and was then replaced w/ the loop. how did they fit the ball-point pen in the enclosure?

[11-90-an]

how did they fit the ball-point pen in the enclosure?

Pedalbuilders manage to squeeze everything into such tiny boxes these days...

[StephenGiles]

Thanks Mark. that's given me a clue as to where my schematic is!

I've found the redraw Mark, which I did in 2000 and updated with an 8 stage version in 2004! Unfortunately the excel drawing looks slightly odd in Excel 2019 for some reason - another lockdown job!!