Sansamp gt2 debug

[esmifra]

Hello everyone!

I've finished building my Sansamp gt2 from www.tonepad.com and it doesn't work. I've checked the solder spots and they seem fine, and i can't find any bridges. What i see is that i have 8.92V everywhere.. and i mean everywhere, every pin of every IC has 8.92V and the ground also has 8.92V, and the transistor too.

ICs: TL088CN
transistor:BC5498
(i was told these would be equivalent, with the transistor bieng mounted backwards)

From what i've red, there should be 4.5V at pin8 of every IC and i don't know what to do. I have some dificulty in understanding tecnical english language because its not my native tounge.

Any help would be apreciated

[michauorin]

Do You have a multimeter (voltmeter)?
[edit] sorry, stupid question :|[/]
If not, things will be really hard to check at a distance.
If so:
1. Please check the voltages at IC sockets (if You use them, and one definitely should use them), without the IC's plugged.
Post the results, if everything seems right to You, You can also check the voltages pinpointed by the orange arrows here:


Of course all voltage in reference to PCB ground.

[esmifra]

Hi! thanks for replying

Here are my measurements without the ICs in their sockets

IC1                                            IC2                          IC3                          IC4

pin1: 0V                              pin1: 0V                    pin1: 0V                   pin1: 0V
pin2: 0V                              pin2: 0V                    pin2: 0V                   pin2: 0V
pin3: 8.11V                         pin3: 0V                    pin3: 8.86V             pin3: 8.92V
pin4: 8.92V                         pin4: 8.92V              pin4: 8.92V              pin4: 8.92V
pin5: 8.11V                         pin5: 0V                   pin5: 0V                   pin5: 8.92V
pin6: 0V                              pin6: 8.62V              pin6: 8.89V              pin6: 2.63V
pin7: 0v                               pin7: 8.89V             pin7: 8.89V              pin7: 2.61V
pin8: 8.92V                         pin8: 8.92V              pin8: 8.92V             pin8: 8.92V

I measure 8.92V where the arrows point to. Any clue to whats up?

[michauorin]

The orange marked trace on the PCB should be at 4.5v if i read the schematic correctly, i'd look at the voltage divider resistors first, IC 4 pins 3 ad 5 should be at 4.5v. check out if the resistor to the left of 220 uF input capacitors makes correct contact with the pcb pads at both ends.
Also, TL 088 seems to be a standard opamp, all Pin4 should be -vcc, in this case 0V.

Are You sure You count the pins correctly?
Pin1 is the square one, and the pin right next to it is pin8.

Those voltages seem really strange, i'd start by tracing whole the supply lines (red and orange traces on the pcb layout by tone pad), and check out if and where something stops to be correct there.
For some reason on some points that should be at 0 V potential, there's full supply voltage, first You'll have to trace the source of this problem, and then start to try plugging the opamps in (since they may fry otherwise ).
It's a good habit to check the IC socket voltages before even plugging the IC's in.

[esmifra]

The pins should be   1    8  is this correct?
                                 2    7
                                 3    6
                                 4    5
The resistor is well soldered to the board. I believe the voltage divider isn't dividing correctly but i have no clue as to what might be causing this.

This is what my build looks like:

http://i.imgur.com/XOuRP2z.jpg (front)

http://i.imgur.com/Ov2XE5i.jpg (back)

When you say tracing, does that mean i put the black tip of the multimeter in the - part of the batery and with the red tip, i start touching every end of each component? Because if this is it, i've done it and it marks 8.92V on all of them. (red and orange traces).

[Cozybuilder]

Could you post photos front and back of your circuit card?

I suspect you have inadvertently connected +9V to the ground bus.

Edit: Thank you for the photos, you posted while I was typing

I don't see a ground connection, just a blob of solder for the ground wire pad. Broken off?

[esmifra]

I just did

The red wire is the +9V. I disconnected the IN and ground and left only the OUT.

[Cozybuilder]

Reconnect the ground wire, hook it up to power, and remeasure the voltages.

[esmifra]

I'm sorry, i don't unsterstand what "hook it up to power" means. The ground is suposedly conected to the ground of the jack input, correct? do i have to connect it to the negative part of the baterry?

edit:after connecting the ground to the gorund of the jack input, the measurements are the same

[michauorin]

Yes, as both the ground of the jack input and GND are 0v lines. Moreover, it's common to use stereo input jacks to conserve battery life, by shorting the -v from battery to PCB GND only if there is an input jack plugged. (Guitar jacks are exclusively mono, so when the PCB GND is soldered as Sleeve part of the jack, and -v from the battery as Ring part of the jack these two are shorted only if there is a mono jack plugged. Otherwise there's no way for current to flow)

Hook it up to power means essentialy reconnect the power

[Cozybuilder]

Ground is the reference to the neg terminal of the battery. It must be connected to make measurements.

[esmifra]

I've tried both ways ( connecting the ground to jack ground and connecting ground to the - of the batery)

With the ground on input jack ( its stereo) it has 8.92V everywhere and the other way didn't work at all, so i guess the ground to the jack input ground is the right way

Its hard to isolate the problem because i get the same measurement everywhere, from the +9V to the output signal and the ground. Something must be shorting somewhere.



Edit: i noticed that when i plugged the jack into the input, i got a drop of Voltage. I'll take measurements with the jack plugged in and report again

[esmifra]

IC1                             IC2                        IC3                        IC4

pin1:0V                  pin1:0V                    pin1:0V                 pin1:
pin2:0V                  pin2:0V                    pin2:0V                 pin2:
pin3:4.07V             pin3:0V                    pin3:4.45V            pin3:4.46V
pin4:0V                  pin4:0V                    pin4:0V                 pin4:
pin5:4.07V             pin5:0V                    pin5:0V                 pin5:4.46V
pin6:0V                  pin6:4.33V               pin6:4.46V           pin6:-1.22V
pin7:0V                  pin7:4.46V               pin7:4.46V           pin7:-1.28V
pin8:8.92V             pin8:8.92V              pin8:8.92V            pin8:8.92V

These values seem more like its all good, right?

Also, the pic with the arrows, at the resistor it measures 4.46V.

The ground measures 0. I don't understand this. Should i put the ICs in and remeasure? I'll reconnect the IN cable also

[michauorin]

These seem a lot more right indeed, now it makes sense to try it with the ICs
The ground should measure 0 V, if it isn't then it shouldn't be called ground

[esmifra]

I've reconnected everything and still no sound.

Voltage didn't change since the previous measurements (8.92V at the red trace and 4.46V at the orange trace and 0 at ground)

I forgot to say that i'm not using any bypass switch. The IN is directly from the jack and the OUT too ( in case this matters)

[michauorin]

So now comes the moment that everyone loves. When the voltages are correct it makes sense to use a signal source (f. ex. guitar) and an audio scope to trace where the signal is lost. It's the most effective way of debugging.

[You can find a complete guide of building and using an audio scope here : http://www.diystompboxes.com/wiki/index.php?title=Debugging ]

[Cozybuilder]

It looks like there are 3 banks of switches- the one on the right is connected with some fairly long exposed leads between the insulation and board- check these to be sure none are shorting out.

[Kipper4]

Have you got all the switches right?
From what I see on the schematic all ICs are TL072 and all referanced to Vb so pins 1 2 3 5 6 7 should all be around 4.5v.
pins4 should all be Gnd 0v
pins8 should all be 9v
You have so many that are 0v or 9v I'm wondering if your power rails are good through out.
Check all your jumpers for continuaty too.

[Cozybuilder]

Rich- the voltages were taken with the chips out.

[Kipper4]

okey dokey my bad