Help With Debug

[grathan]

can someone please help a newbie out. I'm having trouble pinpointing my mistakes. I have double checked the trace cuts, jumpers/wires/ component placements. I checked the pots were functional. INspected tracks for solder. Any tips or things to look for would be greatly appreciated.


http://www.aronnelson.com/gallery/main.php/v/cathexis/Veroboard+Layouts/ProCo+RAT/ProCo+RAT.JPG.html


I get audio signal up to but not past both r8, and c7.

WHen I pull q1 out of the socket, slight audio signal can be heard. Also the image on this layout indicateds gate at the top which is how I have it in the circuit.

The voltages at q1
G = 0.0
S = 9.46
D = 2.16

not sure if relavant vdg -2.00 Vgs -4.72 Vds -7.26

data sheet for lm308n  http://www.futurlec.com/Linear/LM308N.shtml
Ic1 voltages

1 8.57
2 8.75
3 0.56
4 0.00
5 0.00
6 8.80
7 9.46
8 0.32

[Mike Burgundy]

Pull the IC (socketed, right?) and check the voltages. I think either the opamp is fried, or there's something wrong with values or soldering in the voltage devider (R5,6, C6) giving you reference voltage for pin3 (the + input). That should be at 4.5V. If it is without the chip, the chip is probably damaged.

[grathan]

Thanks for looking Mike. When I pull the IC and test for voltage at pin 3 i get about 4 volts and then it slowly decreses to about 2.3 as I hold the meter there.   Perhaps I will try another chip.


Can anyone spot a similar chip to the LM308n in my collection?

7905ct  x1
ad712jnz x1       
CD4007UBE x2
CD40106BE x1
CD40106BPWR x1 (mini)
CD4049UBE x4                 
HA17458  x1
HA17555 x1
HCF40106BEY x2
HCF4047BE x2
icl7660scpa  x1   
JRC386D x1
JRC4558D X1
JRC4558L sb X1
jrc4559   x2                   
KA4558   E133C   x4
L7805cv  x6
L7806cv  x1
L7812cv  x5
L7815cv  x1
L7915cv  x1
lf353 x6                       
LM1458 x10                     
LM308N x2
LM311p x1
LM324n x9
LM339n  x4
LM358N x2
LM358p x4
LM386-N3  sb X6
LM3900N x2
LM567CN x1
LM741CN x3
LM741CM x1 (mini)-
LM833N x3
lm833d x2 (mini)
max1044  x1       
MC34074APG  x1
MC34074PG  x2
MC1458P  x1
MN3007 x9
ne5532 x10             
ne555p x6
ne556n x1
NJM2043D sb JRC2043DD x1
NJM4580d  x4                       
opa2134 x2      socjod
OP2604AP SB X2
tl064bcn  x2                 
TL071CP sb x1
TL072  sb X13
tl074 x5             
tlo82cn x2
tlc2272cp x2
UA741CD x1 (mini)
UA741CN x11
UA741CP  sb x1
RC4558IDR x1 (mini)
RC4558P sb X2
TS555CN x1



Also is c6 supposed to be negative side facing down?