Rat Problems!

[cmat]

Could some one tell me what the voltage is at the transistor and the IC on a Rat?  I built it on a board from GGG.  I have bypass sound and the mil bypass works but no signal comeing from the circuit.  Thanks Guys

[acryl]

i hope this will help you

voltages from my tonepad rat clone (vintage rat) Vbattery 9.25V
1  8.43
2  4.61
3  2.27
4
5
6  4.61
7  9.25
8  4.69
fet  G 0.0  S 1.16  D 9.25

voltages from an original proco rat II (w/ led) Vbattery  9.12v
1  8.35
2  4.53
3  1.38
4
5
6  4.53
7  9.11
8  4.55
fet  G  0.0  S  2.87  D  9.11
      G  0.0  S  2.37  D  9.11


good luck !      acryl

[cmat]

Thanks for the info.  Here is what I have
1 8.56
2 9.3
3 4.3
4 0
5 0
6 9.34
7 9.27
8 6.89 

G 0
S 2.04
D 9.27

all @ 9.33v  I built the board at GGG and I have run through this board 2 many times I have even completly rewired it with no luck.  I believe my problem lies in the circuit.  I dont know why my readings are off.  Any ideas would be appreciated.

[Wild Zebra]

  I not sure if this is still the case, but I used that layout and had problems.  I posted and there was
discussion that the layout is backwards, reversed, what have you.  Search for posts made
by me and you will surely find it.  Needless to say I have made two www.tonepad.com rats
and they work perfectly.

[cmat]

I built it with JD's board and went by the layout there.  Is there a problem with it, an update that I dont know about?  If so can you tell me?  Thanks!

[RDV]

Mine worked fine with the PCB I bought from GGG.

I can tell you that your voltage divider is not working by your readings.

RDV

[RDV]

At the junction of R15 and R16 you should be getting about half of your supply voltage there. If not, make sure they're the correct values(10k).

RDV

[Fp-www.Tonepad.com]

my guess is:

From your voltage readings, I'd say you have a bad cap (reversed, wrong value or just plain broken) either for the 4.7uF or the 2.2uFs (going thru resistors to pin2), that is messing your dc bias.

Fp

[RDV]

Check the polarity of C12(47uF).

RDV

[Fp-www.Tonepad.com]

RDV, while your observation may be correct, I think the vbias supply part is correct given the voltage at pin3.

Fp

[cmat]

Thanks Guys.  I replaced all of the polarized caps with no luck.  I checked the polarity of the caps 15 times thinking I had one backwards and they are correct by the parts layout.  I just dont get why I have absolutely no sound and my voltages are off.

[RDV]

RDV, while your observation may be correct, I think the vbias supply part is correct given the voltage at pin3.

Fp

You're right about Pin 3 but everything else is so far off  I think the IC might be backward?

RDV

[johngreene]

Thanks Guys.  I replaced all of the polarized caps with no luck.  I checked the polarity of the caps 15 times thinking I had one backwards and they are correct by the parts layout.  I just dont get why I have absolutely no sound and my voltages are off.

You're not getting any sound through it because the output is slammed against the upper rail. The fact that both pin 6 and pin 2 are well above pin 3 suggests to me a blown IC. I didn't see in any of your posts where you say you tried a different IC. I would pull the IC, measure all the voltages on the pins with nothing there. You should only measure something on pin 7 and 3. If that is all ok, try a new part.

--john

[cmat]

I have a bleed through of .15v on pin 2 and 7.  I tried 2 diffrent chips in it with no luck

[johngreene]

I have a bleed through of .15v on pin 2 and 7.  I tried 2 diffrent chips in it with no luck

With no chip, Pin 7 should have 9 volts on it. Pin 2 should not have any voltage and pin 3 should have 4.5V.

--john

[RDV]

CMAT:

Which IC are you using?

RDV

[cmat]

I was using a LM308 but I have tried a TL072 and a 4559p in it to check it out.  I believe that positive curent could be leaking onto the negative side somehow but I dont think it is 9v.  I think that may be why there is just a trace amount of current bleeding through on the 2 other pins when the IC is out.  The thing is if this was the case I would think it would be a capacitor bad but I changed the polarized caps.  Do you think one of the film caps could be bad?  I am almost at the point of redoing the whole circuit with all new parts but I want to know what is causing this.  The frustration is really setting in and when you are frustrated the little things can elude you for hours.

[Fp-www.Tonepad.com]

TL072 and 4559 are DUAL opamps. LM308 isn't. They don't share the same pinout.

Try a TL071 or LM741 and remove the 30pF cap.

Fp

[cmat]

Which IC is supposed to be in it?  I thought a LM308 was.  If my LM308 isnt blown will it work?  I dont have one of the others I will have to order it from small bear.  Thanks for all of the help guys you dont know how much I appreciate it!!

[Fp-www.Tonepad.com]

I don't know GGGs layout, but I'm quite sure it's a single externally compensated opamp.

Fp