RAT Debug help needed

[peps1]

Just got the audio probe out and followed the input path upto the ic, but not sure what to do now?






Have used a LM741 with 30pf cap left out insted of LM308 (do i need a jumper where the 30pf was......as iv not used on  

1.What does it do, not do, and sound like= No audio
2.Name of the circuit = La Rata
3.Source of the circuit (URL of schematic or project) = tonepad
4.Any modifications to the circuit? = 30pf cap left out as using 2N5457
5.Any parts substitutions=
2N5457 insted of a 2N5458
1N4148 insted of 1N914
LM741 with 30pf cap left out insted of LM308

Q1 =2N5457
D =9.5
G =1.58
S =0



IC1 LM741
P1 7.65
P2 7.79
P3 7.13
P4 7.65
P5 0
P6 9.50
P7 7.78
P8 7.66

D1
A (anode, the non-band end) = 0.96
K (cathode, the banded end) = 1.23

D2
A = 1.11
K = 0.95

D3
A = 9.50
K = 0

[petemoore]

IC1 LM741
P1 7.65
P2 7.79
P3 7.13
P4 7.65  When this one reads 0.0v =Gnd. the other pin bias's'll change too
P5 0
P6 9.50
P7 7.78
P8 7.66

[peps1]

.......um...........um..........?

[oldrocker]

Up to the ic?  Do you mean pin3? Do you have sound out of pin6?  No jumper or cap needed btwn pin1 and 8 when using a 741.

[peps1]

Pin 3 is the only pin on the IC that has any output, no sound out of pin6.

[Scruffie]

.......um...........um..........?

I think he means Pin 4 should be 0V as it's the ground... try and look for and solder bridges that might be causing it to get a voltage.

Also is your FET in the right way? Your Gate should be getting 0V and the S getting the 1.58V and the D the 9.5V I think.

[peps1]

Had a cold solder on pin 4 (GND) so switched out the LM741 for a new one, in-case I had damaged it.....but still no audio on pin 6 or 2?

here are the new readings

IC1 LM741
P1 0v
P2 1.91v
P3 0v
P4 0v
p5 0v
p6 1.91v
p7 9.5v
p8 0v

[Scruffie]

Did you check your FET pinout?

Had a search and found some voltages from a working tonepad Rat:
1  8.43
2  4.61
3  2.27
4  0.00
5  0.00
6  4.61
7  9.25
8  4.69
FET  G 0.0  S 1.16  D 9.25

So yours are pretty far off this...

[oldrocker]

Pin 7 should be at 9 volts.  I don't pin 6 should be that high.  Yes look at Scuffles voltages.

[peps1]

Did you check your FET pinout?

Had a search and found some voltages from a working tonepad Rat:
1  8.43
2  4.61
3  2.27
4  0.00
5  0.00
6  4.61
7  9.25
8  4.69
FET  G 0.0  S 1.16  D 9.25

So yours are pretty far off this...

just a little far off!

Here is my FET orientation and v (and its a 2N5457 insted of a 2N5458)



ETA:

TOTALLY BUGGERED UP MY PIN READINGS.....the are as follows!

P1 0v
P2 1.91v
P3 0v
P4 0v
p5 0v
p6 1.91v
p7 9.5v
p8 0v

[Scruffie]

Ah the FET's fine now, you gave it as
Q1 =2N5457
D =9.5
G =1.58
S =0
Before which wasn't right.

As for the rest of the voltages... I guess look for any more cold joints... Correct Op-Amp orientation... Backwards Orientated Electrolytic Capacitors.

[peps1]

Ah the FET's fine now, you gave it as
Q1 =2N5457
D =9.5
G =1.58
S =0
Before which wasn't right.

As for the rest of the voltages... I guess look for any more cold joints... Correct Op-Amp orientation... Backwards Orientated Electrolytic Capacitors.

Sorry about that, as you can see I cant even count IC pins in the right order today!!! 

[petemoore]

P1 0v  Compensation pin, never had anything but a cap here, no matter Owise
P2 1.91v    This is an input pin, 1/2v of supply for an input pin works, usually.
P3 0v ''They've'' got voltage shown here too, an input pin, check for ground here.
P4 0v  Ground, but is it touching pin 3 ?
p5 0v  a not connected pin IIRC
p6 1.91v  Output pin is following the V difference between the input pins?
p7 9.5v   A good voltage for Rat running.
p8 0v  Compensation pins, put some little C between them.
  Something with pin 2 and 3...check the voltage divider [two equal value resistors strewn between and splitting the supply voltages [9v+ and 0V=Gnd.
  You should get 1/2v of supply at the junction of the two divider resistors, measure their R values.

[peps1]

Taken some time off from this evil debug....but back on it now!


@ pete, first off all thank you for all the help.

P1 0v  Compensation pin, never had anything but a cap here, no matter Owise
Not used a cap her to bridge with P8
P2 1.91v    This is an input pin, 1/2v of supply for an input pin works, usually.
only getting 1.91v here
P3 0v ''They've'' got voltage shown here too, an input pin, check for ground here.
Nope, looks like a good clean solder, with no bridge to P4
P4 0v  Ground, but is it touching pin 3 ?
As above
p5 0v  a not connected pin IIRC
your right
p6 1.91v  Output pin is following the V difference between the input pins?
pardon?
p7 9.5v   A good voltage for Rat running.
well thats one thing thats gone rightvwith this build
p8 0v  Compensation pins, put some little C between them.
how small a cap?

 Something with pin 2 and 3...check the voltage divider [two equal value resistors strewn between and splitting the supply voltages [9v+ and 0V=Gnd.
 You should get 1/2v of supply at the junction of the two divider resistors, measure their R values.
can you draw that for me?

[peps1]

Switched out the IC/dill and seem to have a little progress, but audio is killed off at the 1k resistor on the filter pot?

the distort pot also massively increases the volume,massively!

[richon]

1K resistor (the one before the filter) is in the right value or is it a least working?

does it read any sound at D1 and D2?

[peps1]

Think its a 1K, put my DMM to 20k and it reads 1.00 across it.

No audio at D1 or D2 

[jkokura]

Check the connection on that 1K resistor, cause that's where the sound goes through on the Schematic at least. Check the joint, then if it seems fine, try changing out the 1K resistor for a new one, cause it might just be broken.

Jacob

[peps1]

Check the connection on that 1K resistor, cause that's where the sound goes through on the Schematic at least. Check the joint, then if it seems fine, try changing out the 1K resistor for a new one, cause it might just be broken.

Jacob

switched the 1k, checked connection, but still no audio

[jkokura]

Hmmm...

Following the schem, and following the layout, that's the obvious problem. If you're not getting sound on the other side of that 1K resistor on the way to the filtering area, you're not going to get sound at the output. I'm glad you changed it out, and I feel terrible that it's still not working. The reason I feel terrible is because I have to tell you to keep testing in an around that area. It might be as simple as you resoldered that 1K in poorly when you redid it, but it might be as bad as a problem in the board.

Did you get the board from Tonepad, or did you make it yourself? Can you see the traces?

Jacob