MXR Micro Flanger - no modulation

[shalebridge]

I have been probing this circuit for a while now but still can't seem to track down this problem.  When I put a scope on pin 1 of the SAD512D I get a pulse wave, but there is no rate oscillation - the flange is stuck at a certain point along its sweep and I can hear that in the effect output.  I have searched for shorts/bad tantalums, and replaced all but the .33 tants around the TL062 and the 15uf cap at the TL061.  Replacing the TL061 and the 4069 didn't seem to make a difference, unless the used 61's I had were toast already.  The transistors test good as well (in circuit).  Adjusting the trim changes nothing except for distortion at the level of the flange sweep.    Any help would be appreciated, thanks!

[Mark Hammer]

I have a Commande Series flanger, which is very very similar to the Micro-Flanger.  A bad CD4069 prevented it from functioning properly, and a replacement restored it.  The 4069 coverts the lLFO to a HF clock.  No clock, no flange sweep.

[Govmnt_Lacky]

@shalebridge

From your description, it sounds like your flanger is working more like a filter matrix. When you say "the flange is stuck at a certain point along its sweep and I can hear that in the effect output," this is what I am thinking of.

IF that IS the case, then the problem lies with your LFO section or where the LFO is mixing with the delayed signal. My suggestion would be to double check the wiring to your RATE pot to make sure it is OK and also check the rate pot's PCB connections too.

After that, you should go here:

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Follow the instructions and repost.

Good Luck 

[shalebridge]

Alright, here we go on the debugging list:

1)  Pulse wave output but no modulation.  Sounds like straight filtering.
2) MXR Micro-Flanger
3) http://i414.photobucket.com/albums/pp228/Mark_Hammer/Micro20Flanger-1.jpg
4) Mods:  Previous owner installed IC socket for 4069 and new battery clip..  I installed sockets on OP-AMPS.  Wasn't working previous to my installation.  
5) C20 (3.3uf) replaced with aluminum electrolytic.  C19 (10uf) replaced.  Also not working previous to this change.
6)
7) Out of circuit voltage of battery is 9.02V.  Voltage at red circuit lead started at 8.5V, slowly going up to 8.88V.  These readings are the same with/without any IC's installed.  Voltage at black lead 0V

U-1A/B (TL062CP):
    Pin 1: 3.31
    Pin 2: 3.31
    Pin 3: 1.47
    Pin 4: 0
    Pin 5: 2.65 (variable range 1.97/3.57 by the trimpot)
    Pin 6: 3.86
    Pin 7: 3.86
    Pin 8: 8.84

U-4 (TL061CP):
    Pin 1: .07
    Pin 2: Rate up- 4.71, Rate down- 4.82
    Pin 3: Rate up- 2.92, Rate down- 2.84
    Pin 4: 0
    Pin 5: .07
    Pin 6: Rate down- 4.33, Rate up- 4.38
    Pin 7: 8.62
    Pin 8: 0

U-2 (CD4069UBE):
    Pin 1: 0
    Pin 2: 8.82
    Pin 3: 0
    Pin 4: 8.81
    Pin 5: 0
    Pin 6: 8.81
    Pin 7: 0
    Pin 8: .84
    Pin 9: 6.56
    Pin 10: .55
    Pin 11: 8.14
    Pin 12: 8.14
    Pin 13: .84
    Pin 14: 8.8

A-3 (SAD512D):
    Pin 1: .55
    Pin 2: 0
    Pin 3: 3.87
    Pin 4: 3.87
    Pin 5: 8.8
    Pin 6: 1.5
    Pin 7: 0
    Pin 8: 8.8

Q-1 (ZTX109C):
    C: 8.8
    B: 2.06
    E: 1.74

Q-2: (ZTX109C):
    C: 8.8
    B: 3.46
    E: 3.27

Q-3: (2N4126):
    E: 8.79
    B: 8.55
    C: 6.67

Q-4 (ZTX109C):
    C: .53
    B: .53
    E: 0

Q-5 (ZTX109C):
    C: 6.67
    B: .59
    E: 0

C-2 (.33 tant):
    +: 3.05
     -:0

C-14 (.33 tant):
    +: 3.83
     -: 0

C-18 (15uf alum. electrolytic):
    +: 4.35
     -: 0

C-19 (10uf alum. electrolytic):
    +: 8.57
     -: 0

C-20 (3.3uf alum. electrolytic):
    +: .59
     -: 0

Battery power steadily dropped to 8.77 while testing.

If I had my scope with me right now I would send pictures of the waves I am getting off of the 4069.  Hopefully this info can help.  I have successfully diagnosed and repaired the larger MXR Flanger but I haven't worked on one with a hex inverter as a clock driver.

[Fender3D]

The 3 inverter clock VCO is an MXR trademark.
On M117 they used half 4013 to achieve the same goal...

One advantage with SAD512D is that you don't need a proper square wave clock signal, anything "pulsing" will work

Here, you have no LFO voltage from TL061
Voltage at pin 2 should "move" somewhat...
Check around that area...

BTW
micro's PCB is double face, maybe any up-down connection is failing...

[Mark Hammer]

They could use that clock because the SAD512D only requires the single-phase "tick" clock pulse, and not the tick and the tock.  The conversion of a single clock pulse into two complementary pulses is done internally....which is one of the primary reasons why SAD512D circuits do not lend themselves to substitution of other delay chips....which, in turn, is part of what leads to the cost of those chips in the NOS market: there is nothing else you can use instead.

[shalebridge]

Alright, my other TL061s seem to not work.  

The MXR circuit seems to be VERY picky about what op-amp goes there. The only time I ever got an oscillation out of Pin 2 was by using an LM301AN, and with that I only got a sweep manually by turning the Rate pot.  741's don't work at all, TL071/081 don't seem to either.  Waiting on a batch of new 61's to come in and test.  Thanks for the help so far!

Edit:  I do know that the 61 is a low power op-amp, I was just curious if I could get anything out of it with the other versions.

[shalebridge]

So I received my lot of TL061's...and no change.  All IC's are new and tested in other circuits, replaced the 15uf cap, and I even resoldered all of the connections.  Still acts as a filter with no modulation.  Could be an out of spec resistor somewhere?

Here are two hints that may help:
    -If I touch the sides of Tl061, the sweep drops to a lower frequency.  When I let go it sweeps back up and holds at a higher frequency.
    -If I ground the center wiper of the rate pot, it moves the sweep as well.  Still no modulation though...


I checked for shorts/open connections on all the IC sockets, and checked connections between pots and PCB.  This is really starting to bug me.

[Fender3D]

Lift R41 and hook your DVM to R30-R31 node.
You should have "moving" LFO voltage there.
Otherwise, you have just 6 resistors (R33 is useless) and 3 capacitors away...
Did you check C17, didn't you?

[Govmnt_Lacky]

Is the voltage on Q4 Collector and Base correct? Doesn't seem right to me  

This is really starting to bug me.

Hence the term "Debugging!" 

[shalebridge]

So after completely removing and replacing the solder around Q4 and R39 I started getting voltage sweeps from U4. Someone had previously either replaced or resoldered the transistors so I had just assumed since they looked freshly soldered they were "fine". D'oh!   

@Govmnt_Lacky: I agree with you that the voltage at Q4 looks wrong.  9V to 1megohm should be around 4.5V but instead still reads around .5V. 

The effect works now, and I realize now what people mean when they say these don't have quite a deep flange.  I wonder if changing C18 or R33 would affect the sweep speed? 

Thank you all for your help!  All of the information I learned here has been invaluable.

[Govmnt_Lacky]

Still might be worth it to double check ALL of your semiconductors (ICs, transistors, etc.) to make sure they are "what is supposed to be there."

Make sure all of your NPN transistors are in fact NPN, all PNPs are PNP, etc.

If someone decided to swap them and didnt verify their work (hence your problems), whats to say they didn't slack off when verifying proper components? 

[Fender3D]

I removed R33 on mine, and subbed Rate pot with 1MC, for a different speed

You might lift R39 (maybe 470K or lower will work better) and connect it to a 100K pot/trimmer wiper, running from GND to +V... for a different range

[shalebridge]

While checking out the other components to make sure they are correct (they are), the pedal mysteriously quit again, turning into a high impedance noise nightmare when I got near it.  Now upon VERY close inspection at all of the resistors around the LFO, I discovered an extremely small hairline crack on one of the 1M resistors.  For good measure I just replaced all of them with matched ones.  Now it works trouble free and sounds even better than when I got it working earlier yesterday. 

Now to mod...