weird issue on my "layout" of Bluesbreaker (GGG w/ True Bypass)

[jplebre]

Hey guys

A bit of a weird issue on my layout of the GGG.
(yeah, I know I could just etch it but laying a new schematic and layout in eagle is part of the fun for me!)

Anyways, new layout so I might have done some silly things around here.




First thing I noticed was... forgot to add a patch point for the ground... Doh!!!!!!

Now, Sine wavy goes in, sine wavy is present on first resistor, first cap, all the way to IC1 - leg 3.
Also, on the input side of the 1M resistor (R4).

The weird bit is, nothing comes out, but on IC1 - leg 1 there's 9v present :S
Same on the IC side of the 47pF cap.

No shorts that I can see, changing the pot makes no difference. there is no AC signal there.

Have I missed something as stupid as the ground? I'll probably be able to see it in a couple of days but I spent the whole weekend on this!

Ty

[jplebre]

just realized the layout+parts looks confusing as the legs of resistors look like more traces.
here's the layout as well

[PRR]

> Have I missed something as stupid as the ground?

Wall, I shore don't see any designated ground-pad connection point:



Basic layout check: all external connections accounted for.

Basic smoke-test check: DC voltages first. If all points are 9V DC relative to battery neg snap, you fergot power ground.

[jplebre]

Hey PRR

Thanks for your awesome reply!

I did noticed missing the ground so I quickly drilled one hole and improvised a pad. Enough to keep me testing a bit more.

And most points are 4v ish DC relative to battery ground. I liked your idea will colour the bits where I see voltages maybe people can help me a bit more then

Thanks!

[jplebre]

I know I've been away but I haven't had enough free time to justify turning my living room into a science lab.
I finally spent the afternoon with my osc.

I know the ground is not in the schem yet (already added it for v0.7 on Eagle )

So this is what I've got (Ty PRR for the idea!)


Red - 9V DC
Yellow - original sine AC
Purple - biased sine AC
Green - Ground
orange - 4v DC (aprox - bias voltage?)
Blue - residual DC (less than 1v)
black - 0v ac and DC

Turning pots does nothing

I don't think i done a bad job on soldering (etching didn't go as well as my first attempts).


Anyone?

Much appreciated!

[slacker]

If you used a socket remove the opamp and measure the voltage in the pin 1 spot, if it's still 9 volts then you have some sort of short to 9 volts, possibly via pin 8.
If it measures 0 volts, which it should do, then the most likely cause is a bad opamp.

[jplebre]

I'll reply in a couple of seconds.
I thought it could have been, but its too far away from the 9v bit, and 3 opamps (same number) showed the same problem.

[jplebre]

Swapped the opamp.
Got a square wave now. Rest of the circuit the same, but pin 1 and the leg of the cap next to pin 1 form a square wave, same frequency as sine, 7v pk-to-pk 5v average

Fishy. very fishy.
Other leg of cap back at 4v and as I said rest of the circuit the same!

[slacker]

Pot1 could be bad then or you have a bad connection to the pot. If there was no connection between pins 1 and 2 the opamp would act like a comparator and give a big square wave output.

What was the voltage at pin1 with the chip removed?

[jplebre]

0v like you predicted

[jplebre]

Think I got it....

For some reason I've put cap C4 going to v-ref, instead of ground.
Bloody hell I'll dig out all the schems I have if I indeed imagined that "VA" point instead of ground...



ROOOOOOOAAAAAAAAAAAAAAAAAAAAAR