MXR Micro Flanger Debugging

[seten]

Thanks everyone - I replaced the 50pf  cap with a 47pf cap (Is that a big enough difference in this situation that I should replace with a new 50pf once I get the rest of the pedal working?)  and still only clean signal but new voltages on the ic.
1 - 0v
2- *
3- 0v
4- *
5- 0v
6- *
7- 0v

Everything with a star (and 8-14) is giving me seemingly random voltages in the mV - they seem to be increasing for a while and then at some random point theyll start decreasing but I cant figure out any sort of pattern. like when I jumped from 2 to 4 my reading for 4 started where 2 left off as it was increasing. I dont think these are clock voltages because I'd assume those follow some sort of pattern - increasing then decreasing within a range or something like that. Seems I went backwards here,  did I mess something up when I changed that cap?

As soon as I get the sockets I'll check for shorts, unless you guys have any suggestions in the mean time.

[duck_arse]

the circuit diagram I can see shows those three invertors as tied off and unused. with each of those 3 input pins tied HARD to ground, the 3 output pins should be just as HARD to V+. something has changed?

[ElectricDruid]

I replaced the 50pf  cap with a 47pf cap (Is that a big enough difference in this situation that I should replace with a new 50pf once I get the rest of the pedal working?)

No, not at all important. 47pf to 50pF is 3pF difference. Even 5pF difference would only be 10%, and little caps like that are often +/-20%.

[Slowpoke101]

Perhaps the most important question concerning the 4069 is; What happened to the volts (9V DC ) on pin 14 ? Broken track ?

[Govmnt_Lacky]

Perhaps the most important question concerning the 4069 is; What happened to the volts (9V DC ) on pin 14 ? Broken track ?

Agreed!

Like I mentioned before... you need to just hold off and wait for the socket. Once it arrives, make sure that all of the traces from the 4069 are still good and go to their respective places in the circuit. Carefully solder in the socket. Then, check for shorts/bridges. Once you know you have no problems, then you can try different 4069 ICs.

Otherwise, all of this soldering parts in and out are going to lead to broken traces and many other problems.

[seten]

Got the socket, putting it in fixed whayever was shorting out the power rail. should be looking for a short (and any ideas where) or are these chips bad?

voltages on socket (no chip)
1 - 9
2-  0-200mV (increasing then starts over)
3- 9
4- 9
5- 1 (varies inconsistently but remains around 1 +/- .05v
6- 9
7- same as 2
8- 0
9- disconnected
10- 0
11- disconnected
12- 0
13- disconnected
14 - 0

[Slowpoke101]

At first glance your voltages on the 4069 socket look really crazy. But light dawned eventually and I came to the conclusion that you've got the pins labelled incorrectly.

The left column is actual pin number. The number after the (= ) symbol is the OP's pin numbering and then the rightmost column is the measured voltage;

14 = 1 - 9V
13 = 2-  0-200mV (increasing then starts over)
12 = 3- 9V
11 = 4- 9V
10 = 5- 1 (varies inconsistently but remains around 1 +/- .05v
9   = 6- 9V
8   = 7- same as 2
7   = 8- 0V
6   = 9- disconnected
5   = 10- 0V
4   = 11- disconnected
3   = 12- 0V
2   = 13- disconnected
1   =  14 - 0V



The voltages appear to be OK. Try installing a replacement 4069 and measure the voltages again.

[seten]

At first glance your voltages on the 4069 socket look really crazy. But light dawned eventually and I came to the conclusion that you've got the pins labelled incorrectly.

The left column is actual pin number. The number after the (= ) symbol is the OP's pin numbering and then the rightmost column is the measured voltage;

14 = 1 - 9V
13 = 2-  0-200mV (increasing then starts over)
12 = 3- 9V
11 = 4- 9V
10 = 5- 1 (varies inconsistently but remains around 1 +/- .05v
9   = 6- 9V
8   = 7- same as 2
7   = 8- 0V
6   = 9- disconnected
5   = 10- 0V
4   = 11- disconnected
3   = 12- 0V
2   = 13- disconnected
1   =  14 - 0V



The voltages appear to be OK. Try installing a replacement 4069 and measure the voltages again.

Whoops yeah you're totally right.

With the chip in:

1- 0v
2- 9v
3- 0v
4- 9v
5- 0v
6- 5.8v
7- 0v
8- 1.3v
9- 9v
10- 1.3v
11- 9v
12- 9v
13- 1.3v
14- 9v

[Slowpoke101]

In the following image I have marked some components and their pins. Q3 and Q5 are of interest. You may have damaged one of them with your test probe mishap. C20 (3.3uF Tantalum ) may also be of concern.



On the transistors you should measure voltages similar to the following voltages;

Q3 C= 7.26V     Q4 C= 0.5V      Q5 C= 7.26V
     B= 8.9V           B= 0.5V           B= 0.5V
     E= 9.0V           E= 0V              E= 0V

The 4069 should have voltages similar to the following;

1= 0V        14= 9V
2= 9V        13= 0.35V (varies )
3= 0V        12= 9V (varies )
4= 9V        11= 9V (varies )
5= 0V        10= 0.05V (varies )
6= 9V         9= 7.2V (varies )
7= 0V         8= 0.35V (varies )

Take some more measurements and see what differences there are.

[seten]

In the following image I have marked some components and their pins. Q3 and Q5 are of interest. You may have damaged one of them with your test probe mishap. C20 (3.3uF Tantalum ) may also be of concern.



On the transistors you should measure voltages similar to the following voltages;

Q3 C= 7.26V     Q4 C= 0.5V      Q5 C= 7.26V
     B= 8.9V           B= 0.5V           B= 0.5V
     E= 9.0V           E= 0V              E= 0V

The 4069 should have voltages similar to the following;

1= 0V        14= 9V
2= 9V        13= 0.35V (varies )
3= 0V        12= 9V (varies )
4= 9V        11= 9V (varies )
5= 0V        10= 0.05V (varies )
6= 9V         9= 7.2V (varies )
7= 0V         8= 0.35V (varies )

Take some more measurements and see what differences there are.

Q3 C= 9.37V     Q4 C= 0.5V      Q5 C= 9.37V
     B= 9.37V          B= 0.5V           B= 0.6V
     E= 9.37V          E= 0V              E= 0V

Looks like Q3 is way off and C of Q5 is off. Guessing B is close enough to be okay.

1= 0V        14= 9V
2= 9V        13= 1.3V
3= 0V        12= 9V
4= 9V        11= 9V
5= 0V        10= 1.3V
6= 5.8V         9= 9V
7= 0V         8= 1.3V

Double checked just to make sure. If its not too much trouble I'd love to hear your thought process here for troubleshooting this.
So when you say varies does that mean it should be an AC voltage there and the listed voltage is the DC offset?

Also, theres about  0.6V across C20 and when I disconnect power I can watch the voltage discharge down to 0 so seems to be working correctly.

[Slowpoke101]

Q3 seems to be shorted. I recommend replacing it. A 2N3906 or 2N5087 should be suitable. Basically just a standard PNP transistor should do the job.
Q5's collector is off due to Q3 not behaving correctly.

One thing that I really am wondering about is the voltage on pin6 of the 4069. Just ignore it for the moment.

My thought processes with this repair are quite simple. I quickly built this part of the circuit and I'm comparing your results with mine. Just for interest's sake, this little oscillator can vary from 16kHz to 1.35MHz which is quite interesting but not really important.

Edit:
C20 seems to be behaving itself which is good.

The voltages that I mention as varying refers to that the measured voltage is not fixed but changes slightly. This change depends on what the LFO is doing.

[seten]

Q3 seems to be shorted. I recommend replacing it. A 2N3906 or 2N5087 should be suitable. Basically just a standard PNP transistor should do the job.
Q5's collector is off due to Q3 not behaving correctly.

One thing that I really am wondering about is the voltage on pin6 of the 4069. Just ignore it for the moment.

My thought processes with this repair are quite simple. I quickly built this part of the circuit and I'm comparing your results with mine. Just for interest's sake, this little oscillator can vary from 16kHz to 1.35MHz which is quite interesting but not really important.

Edit:
C20 seems to be behaving itself which is good.

The voltages that I mention as varying refers to that the measured voltage is not fixed but changes slightly. This change depends on what the LFO is doing.

Q3 C= 7.2V     Q4 C= 0.5V      Q5 C= 7.2V
     B= 9.1V           B= 0.5V           B= 0.6V
     E= 9.38V          E= 0V              E= 0V

Btw, anywhere I was putting 9.0V before I really meant 9.38V.

1= 0V        14= 9.38V
2= 9V        13= 2.5V (varies)
3= 0V        12= 8.5V (varies)
4= 9V        11= 8.5V (varies)
5= 0V        10= 2.5V (varies)
6= 5.8V         9= 7.2V (varies)
7= 0V         8= 2.5V (varies)

Looks like we're getting there! so now just 6 and 13/10/8?

[Slowpoke101]

Looks good. Pin 6 is odd but just ignore it for the moment.
The other pins seem to be what I would expect with the 4069 running at a higher frequency (which is good ).

Connect everything up and see what happens with a guitar connected.

[seten]

Looks good. Pin 6 is odd but just ignore it for the moment.
The other pins seem to be what I would expect with the 4069 running at a higher frequency (which is good ).

Connect everything up and see what happens with a guitar connected.

Got flange! So what about that pin 6?

[Slowpoke101]

It flanges. Good work. Great news 

With pin 6, just make sure that there is nothing touching it - piece of wire, splash of solder, whatever. If all is good, just ignore it for the moment. I don't think that it will cause problems. It may just be an odd RF noise pick-up with your meter being so close to what is a actually a transmitter.