PROBLEMS WHIT MXR DISTORTION+

[j0shua]

I made 5 PCB of MXR distortion+ from ( TONEPAD.COM ), i Assenbly 2 units 1 for me about 2 months and one for a friend , but i soldering all items like the others and not work , the clean sound is ok , when i press the button , no change...... i check the soldering again 1 by 1 , and don't have cold soldering or chort circuit , i change the IC 741 from socket and no change ...... what more can i do




BTW : i check the PCB ( continuity testing ) before soldering!

          H E L P !

[j0shua]

ooops sorry...... the first 2 MXR works ok!...

the new one don't work!

[Fret Wire]

Post the IC pin voltages.

[j0shua]

this is the pin voltage f the LM741 IC

1- 0.0
2- 4.38
3- 1.85
4- 0.0
5- 0.0
6- 4.59
7- 9.33
8- 0.0

[Fret Wire]

Pin 2 should be about 1/2 battery voltage like pin 6. Pin 3 should be about 3.5 -3.7v. Check the soldering/component values/orientation of components coming off pin 3.

[j0shua]

i check all components arround the pin #3 , and cold soldering , is all OK!
but the voltage of pin 3 still in  1.85  

but i need to tell  i change some items because i don't have for example

Original C5 is 10Pf and i change for  0.01Uf  ( ARE MATCH )
Original C4 is 0.47 Uf and i put 0.01 Uf  


*** C4 IS CONECTED TO IC PIN #2
*** C5 IS CONECTED TO IC PIN #2

[j0shua]

I found a R-9 (10k) Resistor  soldering error lol! ..... i put in the not correct side!

im going to resolder again ,.......

[j0shua]

DAMM I CAN'T FIND THE ERROR ON THE PEDAL

i check all pins from IC

1- 0.0
2- 4.38
3- 1.85  
4- 0.0
5- 0.0
6- 4.39
7- 9.33
8- 0.0

i check complete soldering again and again, i change the wrong side R9 resistor ( 10k ), the battery is ok! , the PCB continuiti is ok and not short circuit on PCB or Soldering ....the only change i do from original schematic is the 10 Pf cap to 0.01uF, are match , and the 0.047 Uf in C4 , to o.o1 Uf because i don't find 0.047 cap on stores ...... HELP please

and please tell me the complete pin voltages! of IC

[Fret Wire]

Use this for a voltage guide:
http://www.generalguitargadgets.com/diagrams/dist_ic.gif
Most single Op Amp ckts of this type will show the same voltages.

Check the pos/neg orientation of C1 and C6, and check for solder bridges between the IC pins and the components on each side of the IC. They are stacked in there pretty tight. Use a magnifying glass, because a hair line solder strand can cause these kind of problems.

Your substitutions are going to sound odd. The 10pf cap is to smooth out harsh highs caused by silicon diodes. The TS-9, for example uses a 51pf cap, and you are subbing a .01uf (10,000pf) cap. It will sound very dull and lifeless. If you are using Ge diodes, you can leave the cap out. The .047uf cap basically controls how much bass response is cut out of the signal before it gets amplified. The stock corner frequency is 720hz, your substitution of .01uf will yield a cutoff of 3388hz. You probably wouldn't like the sound of this too much.

[j0shua]

FRET WIRE:

because a hair line solder strand can cause these kind of problems.


thanks for your help , i use a Mgnifier Glass and found some hair solder
(3 ) , now the pin #3 = 4.4v......

it's 2 Am here, so i can't test hehe......

i do a test tomorrow and post here the results ....

once again thanks Fret

[j0shua]

Sound test ok...... As you say i need to put the 10 Pf hehe , the sound is to low , but thanks to you i fixed.... im going to post here some pictures of some parts i found on old  PC monitor ... i think are caps , but 2 of them have 3 pins , not 2 pins are usual ........

[Fret Wire]

Glad to hear it's working now.

[j0shua]

this is the link :
some parts appears to be caps ....


http://photobucket.com/albums/v669/teknoblaster/?action=view¤t=some.jpg

[Fret Wire]

Can't help you with the caps, but for the transistors, go NTE and use their cross reference match. They also have their Quick-cross ver. 11 out for downloading, so you don't have to go to their site every time. They aren't always a perfect match, but will give you a close idea what your semiconductor is.

http://www.nteinc.com/

[j0shua]

Oh! im sorry hehe ( bad english ) , i have  all data from  transistors , i like to know about if those green items are caps... and 1 of then have 3 pins , not 2 as usual ...... thanks!