Another MXR Filter Debug thread

[chicago_mike]

Right now pins 14 of all my IC's are getting close to 4 volts.

I didnt put back in a 100K trimmer in place of R16. Using the TONEPAD layout.

I finally get audio to pass thru but no filtering.

I know about the clock voltages being 1.62 for TI's to work. Just to help my dumb ass out. Is pin 14 on the IC's the clock voltage? Or is it another pin that I look for 1.62 volts?

Thanks.

[StephenGiles]

It is well known that I breadboarded this perhaps 10 years ago using a 4049 instead of a 4069 which I didn't have at the time - any old 4049 and it worked perfectly. I eventually bought a 4069 - any old 4069 and changed the wiring to accomodate the different pin out, and it worked. Maybe I was lucky, I don't know but I don't think so. My samples are floating around somewhere.

[chicago_mike]

Do you think you might have voltages on that unit?

I have the mxr schematic and the build reports and found some info here. So im taking baby steps here really.

[StephenGiles]

Do you think you might have voltages on that unit?

I have the mxr schematic and the build reports and found some info here. So im taking baby steps here really.

No I don't, it came off the breadboard years ago I'm afraid.

[chicago_mike]

Cool. Well I think I might have it boiled down for me.

The scope shows no signal on the 2nd 4069.

Pin 14 shows 3.86 on a fresh 9volt thats pumping out almost 10 vols!

[chicago_mike]

Im pushing a loud 1KHZ signal from cubase ( test tone generator  )

And I get te signal off the 1st and 3rd C's. But the second is dead. I hae more 069's I can try but I think its not te chip.

I dont have a real good way of testing logic chips though.

[chicago_mike]

R7 a 200K

Im geting signal before her but not after. But she measures 200K. Its a 1% metal film.

[chicago_mike]

Well..giving up is one of my specialties.

[chicago_mike]

I dont get this..I cant get the clock voltage under 3.8 volts!

How the hell did anybody get this @#$%ing thing to work?!?

[Mark Hammer]

If you are using the Tonepad layout, one of the things that Francisco is great at is coming up with layouts that have small footprints.  The downside of that is that the solder flux around the pads can make it difficult to spot unintended solder bridges, even with a magnifying glass.  Consequently, one of the first steps I recommend in troubleshooting boards where the components are closely spaced is to apply a bit of methyl hydrate to the copper side with an old toothbrush, and press a paper towel on it to absorb the dissolved flux.  Once you've cleaned off the excess flux, THEN give the board the once over.  There were several occasions when, after doing this, I was able to spot things that had eluded me the first time.

At the very least, you'll be able to confirm for yourself that the problem is NOT the board.

A second set of considerations relates to the use of CMOS chips in this pedal.  I am assuming you used sockets?  Well, that is a LOT of pins that you're depending on to make contact with the socket.  Have all pins properly seated in the sockets? (sometimes they can bend under the chip during insertion without one noticing)  I've found sometimes that pins can acquire corrosion, and a bit of scraping of the pins with a utility blade an help them make contact once inserted.  You may also find that pin contact with budget sockets can sometimes be less reliable than you'd like.  Just a thought.

[chicago_mike]

Hey Mark,

I can confirm the solder is clean and void of bridges. I can confirm that the sockes do make contact. Takes a little bit of time, but testing each and every pin is VERY important. Bent pins are..well...just..UGH!

I'll best this sucker yet. Im too tired to tackle anymore tonight but tomorrow Ill give it another whirl.

But I keep wondering what would cause my voltage issue? I'll have to test it with all my IC's tomorrow but Im sure I already have.

I noticed in one of the many threads about this pedal you mentioned the 1Meg resistor setting Decay time. I wonderif it might be "cool"..I.E. worthwhile to put a 500k resistor and a 500K pot to see if I can alter the decay time? After it works of course.

[Mark Hammer]

A 2:1 change in resistance would provide only minimal difference in decay time.  You probably want a 47k resistor and 1M pot instead.

[chicago_mike]

Okay. Well I get back to debugging her in a few.

Staying positive.