Tonepad TS-808 debug

[mutagenic]

Help needed for my TS-808!

1.Circuit works but no clipping, ie; volume and tone work, but no clipping occurs when the drive pot is turned.
2.Name of the circuit =TS-808 (El Griton 2.2) from Tonepad
3.Source of the circuit (URL of schematic or project) = http://www.tonepad.com/project.asp?id=1
4.Any modifications to the circuit? Assymetric diodes
5.Any parts substitutions? none
6.Positive ground to negative ground conversion? N

Battery voltage=8.99V
Voltage at the circuit board end of the red battery lead =8.97V
Voltage at the circuit board end of the black battery lead =0V


Q1 (2n3904)
C =8.96
B =3.55
E =3.07

Q2(2n3904)
C=8.96
B=0.084
E=0.083

IC1
P1 4.42
P2 4.42
P3 4.42
P4 0
P5 4.42
P6 4.42
P7 4.42
P8 8.97

D1
A (anode, the non-band end) =4.41
K (cathode, the banded end) =4.41

D2
A =4.41
K =4.16

D3
A =4.17
K =4.41

Obviously Q2 doesn't look right.  Also, when I tested the resistance on the 500k log drive pot, I get a range from 34.3 to 46.3k Ohm when it is connected to the circuit.  I removed it, and tested again, and got like 5 to around 500k Ohm, so the pot itself looks fine, just reads funky when in the circuit.
All component values were verified prior to assembly.

Thanks in advance!

[jkokura]

Yep, you already said it. Q2 looks funky. Start looking for solder bridges and poorly soldered joints. Have you double checked that all your parts are correct and oriented right? it's really easy to mix up parts accidentally.

Jacob

[GBlekas]

Q2 readings suggest it is either a transistor not installed in proper orientation (my guess)
Check that collector and emitter are in the right spot.

Or 10k or 510k are not soldered properly.

That's where I would look

[MikeH]

check for solder bridges around the 51k/51pf area off the gain pot.  If there were a bridge between the pads for the 51k R and the 51p Cap, it would cause the 51K resistor to be parallel with the gain pot, instead of series, which would make it read around 45K instead of 500k.  A TS with a 50k gain pot will produce basically no clipping.

If youre getting signal through the circuit just fine, except with no clipping I wouldn't worry too much about the voltage on Q2.

[mutagenic]

Thanks very much for the help guys.  Well, I changed out the 510k from Q2, and although the resistor was fine (re-checked the old one after I removed it), I must have had a cold solder joint because I know have Q2 voltages similar to those I measured for Q1.  I still have only max 45k resistance on the gain pot, but I don't see any solder bridges around the 51k/51pf area.  Would a bad 51pf cap cause the 51k resistor to be in parallel to the 500k pot?  Would this still allow me to get a signal through the circuit, but with no gain?

[Kearns892]

If the 51pf cap is "bad" (shorting the 1st and 2nd lugs of the IC) you will have a short of 0 ohm resistance parallel with the resistor and pot for a grand total of 0 resistance. This short will completely bypass the diodes giving you no clipping.  A short anywhere between legs 1 and 2 would give you signal with no gain, but that doesn't explain your 45k ohm resistance measurement. Can you be more specific as to what resistance you measured?

[Kearns892]

I would bet that your measurement of 45k ohms is the actual value of your 51k resistor due to tolerances in the resistor values. If you get 45k ohms between legs 1 and 2 regardless of the position of the gain pot, then you don't have short between 1 and 2, but you probably have miswired or shorted out the pot. Look to see that the pot is connected properly and it isn't shorted out.

[bamwels]

hi there!!

i want to build this pedal but i have one problem: the tantalum capacitors, are polarized or not?and if they are how can i connect them?

[Fp-www.Tonepad.com]

the tant capacitors are polarized, negative end needs to be pointing towards ground for both of them.

Film capacitors are great for the 0.22uF but you need to find some small ones that'll fit in the board.

Fp