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Vintage MXR Flanger problem

Started by Govmnt_Lacky, September 07, 2011, 09:49:21 AM

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Govmnt_Lacky

September 07, 2011, 09:49:21 AM
I picked up an MXR Flanger (Vintage model with LED) and just had time to crack it open and look at it. So here is the info...

Schematic: http://www.shredaholic.com/mxrflanger.html

Problem: Pedal passes CLEAN signal when on AND off

Voltages: All of the IC voltages are within a few 10ths of a volt from the readings I posted from my clone build here:
http://www.diystompboxes.com/smfforum/index.php?topic=90539.msg774002#msg774002

EXCEPT for the following:

SAD1024 Pins 5 & 6 are reading 5.1 VDC instead of 9.8 VDC.

I did not check transistor voltages as I am wondering if one side of my SAD chip is KA-PUUT!!!

Just looking for some insight and possible confirmation of my findings. Any other ideas would be great as I really do not want to have to replace the SAD  :'(

Thanks for helping!
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Fender3D

#1
September 07, 2011, 10:16:30 AM
Your only hope is a leaking C6...
try and lift it then check pin 5-6 voltage.
you might as well connect C6 lead-to-pins-5-6 at C1-C12 junction just to see if "side B" works...

BTW
clock is present, isn't it?



Otherwise...
My deepest condolences for your SAD  :icon_cry:
"NOT FLAMMABLE" is not a challenge

Govmnt_Lacky

#2
September 07, 2011, 10:21:37 AM Last Edit: September 07, 2011, 10:26:37 AM by Govmnt_Lacky
Quote from: Fender3D on September 07, 2011, 10:16:30 AM
you might as well connect C6 lead-to-pins-5-6 at C1-C12 junction just to see if "side B" works...

Could you explain this  ??? Maybe a little more exact on your explanation as I don't follow your thinking here...

Quote
BTW
clock is present, isn't it?

I will post that here in a few minutes. Gotta wait till lunch to fiddle with more readings. The voltages look good BUT, I will put an oscope to it  ;)

Quote
Otherwise...
My deepest condolences for your SAD  :icon_cry:

Please don't say that  :'(

Also, I am surprised that I am reading voltage at pins 5 & 6 of the SAD. I would think that if that "side" was bad, then it would be 0  ??? Do you have any ideas on that?

Thanks for the help  ;D
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Govmnt_Lacky

#3
September 07, 2011, 11:50:27 AM
Found out something interesting (Maybe?)

I checked at SAD pins 3, 8, 10, and 14 and I am getting a clock signal at all of them (31KHz)

For troubleshooting, I injected a 440Hz/200mV Sine wave at the Input and probed around with my oscope to try to see what was going on. I found something odd...

When the pedal is unplugged from the wall (power removed) I get the full sine wave all the way up to Pin 5 of U4. This is regardless of the switch position (seems normal to me)

However, as soon as I plug the unit into the wall, I get the sine wave on the Input side of C16 but, it is gone after that  ???  This is also regardless of the stomp switch position.

Shouldn't I get some kind of signal after C16 when power is applied?
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Fender56

#4
September 07, 2011, 12:23:00 PM
You should see the sinewave signal after C16, but with a DC offset of Vb, which should be around 7.5V (15V / 2).

Govmnt_Lacky

#5
September 07, 2011, 12:33:28 PM
Quote from: Fender56 on September 07, 2011, 12:23:00 PM
You should see the sinewave signal after C16, but with a DC offset of Vb, which should be around 7.5V (15V / 2).

Thanks F56.

After C16, all I see is what apprears to be a semi-noisy DC signal (about 7.5V as you say) however, there is no sign of a sine wave form  ???

I am wondering what the signal "should" look like. Being at work and looking at this on my spare time, I don't have my working clone here to compare with. I can say that before C16, the signal is a clean 440Hz sinewave. After C16 it is a semi-noisy DC flatline at a 7.5V reference level on the oscope.

Best I can describe it.  :-\
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Fender56

#6
September 07, 2011, 12:48:29 PM
Perhaps the sinewave @ 200mV is not visible at the scale in which your scope is setup in order to see the 7.5V DC level. Put your scope in AC mode, it will be easier to validate your audio signal.

Govmnt_Lacky

#7
September 07, 2011, 01:11:46 PM
Quote from: Fender56 on September 07, 2011, 12:48:29 PM
Perhaps the sinewave @ 200mV is not visible at the scale in which your scope is setup in order to see the 7.5V DC level. Put your scope in AC mode, it will be easier to validate your audio signal.

And again... Thank you F56  ;D

Will reset to AC monitor mode and will repost with findings in a bit.
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Fender3D

#8
September 07, 2011, 02:02:33 PM
Quote from: Govmnt_Lacky on September 07, 2011, 10:21:37 AM
Quote from: Fender3D on September 07, 2011, 10:16:30 AM
you might as well connect C6 lead-to-pins-5-6 at C1-C12 junction just to see if "side B" works...

Could you explain this  ??? Maybe a little more exact on your explanation as I don't follow your thinking here...

SAD1024 has 2 512 stages BBDs:
1 on the left "side" of the chip, and the other on the right "side".
left input is pin2 and outs pins 5 and 6.
right input is pin 15 and outs pins 11 and 12.

In MXR flanger stages are connected in series: signal arrives on pin 2 exits from 5-6 , goes into 15 and finally exits at 11-12
To "jump" first stage you should connect C1 (going to pin 2) to pin 15, without any influences from pins 5-6 (lifting C6).


Quote from: Govmnt_Lacky on September 07, 2011, 10:21:37 AM
Quote
BTW
clock is present, isn't it?

I will post that here in a few minutes. Gotta wait till lunch to fiddle with more readings. The voltages look good BUT, I will put an oscope to it  ;)

OK clock is there...

Quote from: Govmnt_Lacky on September 07, 2011, 10:21:37 AM

Quote
Otherwise...
My deepest condolences for your SAD  :icon_cry:

Please don't say that  :'(

Also, I am surprised that I am reading voltage at pins 5 & 6 of the SAD. I would think that if that "side" was bad, then it would be 0  ??? Do you have any ideas on that?

Thanks for the help  ;D

The outputs MOSFETs have their Ds connected to Vdd so you may have a DC voltage...

"NOT FLAMMABLE" is not a challenge

Govmnt_Lacky

#9
September 07, 2011, 02:15:30 PM
OK. I changed my monitor to AC on the oscope and things look a lot different.

I get a wobbling semi-square waveform on Pins 5 & 6 of the SAD.

I get a slightly different wobbling waveform on Pins 11 & 12 of the SAD.

Other than the clock squarewave I see on the SAD pins, can anyone tell me exactly what I should see at the following points?

SAD Pins 2, 5/6, 15, 11/12
U1 Pins 2 & 1
Output jack tip

It appears that my LFO is working and that the Width, Manual, and Speed pots are working as they seem to adjust the waveform at different points in the circuit.

I do not however, know where to look to see if the Regen is working or even what to look for.

This is all exploratory to me right now. I have the tools at my disposal but I just need to piece together what I should be seeing from some of the more experienced forumites. I am hoping to do this to help others in the future.

I appreciate any and all help that comes my way.

Hopefully, tomorrow I will be able to A/B this with my working clone but for now, I would just like to educate myself with the help of the forum   :icon_wink:
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Govmnt_Lacky

#10
September 07, 2011, 02:42:01 PM
A bit more possibly useful info on this debug:

All controls set fully CCW
Oscope set for AC monitor
400Hz/200mV signal at input:

SAD Pin 2 = 400Hz/335mV Sinewave

SAD Pins 5 & 6 = 32KHz/1.5Vp-p Soft clipped Squarewave

SAD Pin 15 = 32KHz/1.2Vp-p Soft clipped Squarewave

SAD Pins 11 & 12 = 32-580KHz/540-980mV Sawtooth Waveform

This is what I saw on my Oscope. The terminology may be incorrect for pins 11/12 but that is the best way I could describe it.
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Fender3D

#11
September 07, 2011, 03:14:39 PM Last Edit: September 07, 2011, 03:16:52 PM by Fender3D
I can't check for SAD, but I guess you should have:

pin2 = ~double input signal, BTW check its level not just the waveform (it will depend on freq applied)

pin 5-6 = ~signal at pin2, waveform will be "disturbed" by clock chops (you'll want your scope in sinc with the input, cause it might sinc with BBD's clock). You' re working with a sine wave, any "chop" from BBD will look like a dent on your waveform...

pin15= signal at pins 5-6, waveform as above

pin11-12 = ~signal at pin2, waveform more "distorted" by clock chops and slightly dimmed

U1 pin2&1 = ~double input signal, less signal than A1 pin2 though.

with a single sine wave regen may increase or decrease signal at A1's pin 2 [depends on freq applied and delay time (manual)]

EDIT
I'm definitely too slow on replies... your measurements weren't there while typing...
"NOT FLAMMABLE" is not a challenge

Govmnt_Lacky

#12
September 07, 2011, 03:36:06 PM
Quote from: Fender3D on September 07, 2011, 03:14:39 PM
pin 5-6 = ~signal at pin2, waveform will be "disturbed" by clock chops (you'll want your scope in sinc with the input, cause it might sinc with BBD's clock). You' re working with a sine wave, any "chop" from BBD will look like a dent on your waveform...

pin15= signal at pins 5-6, waveform as above

I don't know if I "sync'd with the BBD clock" but the signal at SAD Pins 5, 6, and 15 looked like the clock signal EXCEPT that it had a smaller P-P (1.5V instead of 15V) and the tops of the squarewaves were not flat, they looked clipped a bit.

I think I may just have to wait until I can A/B the measurements with my working clone. That will for sure tell me whether the SAD has crapped out or not.

Fingers crossed!  :icon_eek:
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Govmnt_Lacky

#13
September 07, 2011, 06:55:32 PM
Maybe grasping at straws here but...

Would adjusting R49 (Dist Trim) correct the lower voltage problem I am seeing on Pins 5 & 6 of the SAD?

As stated previously, On my working clone, I get 9.8V on these pins but, on this vintage unit I get 5.1V  ???
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Govmnt_Lacky

#14
September 10, 2011, 08:40:39 AM
It was a bad channel in the SAD chip  :'(

Swapped out with my 1 and only spare and it works like a champ!

I guess I could use this semi-bad chip in a Electric Mistress build possibly. I have heard they work!  ;D
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Fender3D

#15
September 10, 2011, 10:54:35 AM
I'm repeating myself, but reading flanger posts here around, it seems everybody's looking for a shorter BBD to achieve  liquid/jet sound...
You have a wonderful chance:
with a minimal modding (read my previous post, it may be an M117 mod itself) you can have a ìn M117 with 512 stages BBD  :icon_exclaim:
You already have a proper working M117, why don't taste the same performance and control setup, just "higher" ?

Please try and report  :-*
"NOT FLAMMABLE" is not a challenge

Govmnt_Lacky

#16
September 10, 2011, 11:10:23 AM
Quote from: Fender3D on September 10, 2011, 10:54:35 AM
I'm repeating myself, but reading flanger posts here around, it seems everybody's looking for a shorter BBD to achieve  liquid/jet sound...
You have a wonderful chance:
with a minimal modding (read my previous post, it may be an M117 mod itself) you can have a ìn M117 with 512 stages BBD  :icon_exclaim:
You already have a proper working M117, why don't taste the same performance and control setup, just "higher" ?

Please try and report  :-*

Here is my reasoning...

I have (3) M117s. One is a Vintage working unit. NO WAY ON EARTH will I mod that one  :o

I also have 2 working clones. I could mod one of them to try the SAD with the bad channel HOWEVER, I have to weigh the risks.

1) How much chance is there for me to damage the perfectly good SAD that is in there by removing/replacing it?
2) Will the circuit survive the modding? (i.e. traces undamaged, components undamages, etc.)

This may be a job for a whole NEW etch.

-OR-

I can etch a whole new Deluxe Electric Mistress and try the chip in there as I said before. That way, if it does not work out I can try to get another SAD and have a whole new DIFFERENT effect.

Decisions... Decisions...  ???
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Govmnt_Lacky

#17
September 10, 2011, 11:24:05 AM
Quote from: Fender3D on September 07, 2011, 02:02:33 PM
In MXR flanger stages are connected in series: signal arrives on pin 2 exits from 5-6 , goes into 15 and finally exits at 11-12
To "jump" first stage you should connect C1 (going to pin 2) to pin 15, without any influences from pins 5-6 (lifting C6).

If I attempt what you are saying here, would I still need to keep R1, R2, and R49 (trim) in the circuit?

Or, could they be removed and I would essentially be feeding the signal coming out of C1 straight into Pin 15?

Also, could the 2 clock inputs at Pins 3 and 8 be removed since that channel is dead?

Definitely interested in trying this  :icon_wink:
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Fender3D

#18
September 10, 2011, 11:53:37 AM
In the vintage PCB you'll simply lift C1 and C6 then connect one of those caps from C1's right pad (near R1 on PCB) to C6's highest pad (towards C1 on PCB). No tracks cutting needed.

On Madbeans' PCB http://....org/download/file.php?id=13224 you'll desold the jumper in front of IC5, take out C19 and put the jumper from the old jumper's lowest pad (near IC5's pin 16) to C19's leftiest pad (towards IC5).

I guess you shouldn't have any major issues from the remaining connections...

Whether it sounds good, you may put a switch on the working unit and owe me a beer for the mod...  :icon_mrgreen:
"NOT FLAMMABLE" is not a challenge

Govmnt_Lacky

#19
September 10, 2011, 12:09:05 PM
Quote from: Fender3D on September 10, 2011, 11:53:37 AM
In the vintage PCB you'll simply lift C1 and C6 then connect one of those caps from C1's right pad (near R1 on PCB) to C6's highest pad (towards C1 on PCB). No tracks cutting needed.

On Madbeans' PCB http://....org/download/file.php?id=13224 you'll desold the jumper in front of IC5, take out C19 and put the jumper from the old jumper's lowest pad (near IC5's pin 16) to C19's leftiest pad (towards IC5).

I guess you shouldn't have any major issues from the remaining connections...

Whether it sounds good, you may put a switch on the working unit and owe me a beer for the mod...  :icon_mrgreen:

Interesting idea  ;D One of my clones is on the madbean layout!

I may have to investigate the switch idea too. I wonder if this can be done, without any potential damage, to a circuit with a FULLY functional SAD chip  :icon_idea:

Switching the BBD between 512-stage and 1024-stage whenever you want. I am thinking it would need trim adjustments between changes though  :icon_frown:
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'
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