First Build - ITS8 - dead on the bench. :-/

[liam.slack]

Hey all,

Been reading a lot of threads where noobs like me have been helped with their first build, and I was hoping you guys could help me out. Frankly, I'm not entirely sure how to measure much beyond what I've listed below, but I'll gladly take any guidance you guys can offer to figure things out.

At the moment, it's not passing signal, it's not lighting up... it's not doing anything, really. The IC pins are metering exactly as they should (pin 4 is at 288mV, pin 8 is at 9V, the rest are hovering right near 4.5V). Q1 and Q2 both meter at C= 9V, B= 3.7, E= 3.3. Below are pics of the board and switch. Any help would be GREATLY appreciated! This was a birthday present, and it's starting to not feel that way.

Thanks!
Liam

[armdnrdy]

A good front shot of the board and a link to the schematic/project would help further the process.

[R O Tiree]

Hi Liam, and welcome. My initial thoughts...

Pin 4 of the opamp is Ground. It should not read 288mV. It should read 0.000V.

There are 4 holes in the board that are not populated.

Cheers.

[liam.slack]

Hey all,

Thanks for the replies. It's an ITS8 by General Guitar Gadgets. Here is the link to the project:

http://www.generalguitargadgets.com/projects/17-distortion/82-its8-tube-screamer-808-replica-project

And here is a photo of the front of the board.



The unpopulated holes appear right for the project... so what would I do to troubleshoot the ground?

Thanks very much!

-L

Thanks again!

[liam.slack]

UPDATE: I just re-metered the IC, and the ground pin is at 3.5mV. The other pins are at 4.3, with the exception of 8, at 8.72. Does 3.5mV indicate an issue with the ground, or is it within the +- error range of the meter?

Thanks again for your help!

-L

[Jdansti]

1. Where are you placing your other meter probe when you measure the voltages on the chip?

2. What are you using for power?  If you're using a power supply, check that the center (tip) is negative and the sleeve is positive. If you're using a battery, check the polarity.

3. If you're using a power supply, what type of power jack are you using?  If it is metal, you could have some grounding problems.

It appears to me that you could have a fundamental power problem since the LED doesn't light.  Get the LED issue resolved before diving into the rest of the circuit. Your problems might go away once you figure out why the the LED doesn't light.

[liam.slack]

Hey all,

Well, it's sorted. Thanks so much for all your help - it was, of course, something stupid, and entirely my fault.

Turns out I had ALL 3 of the LEDs wired backward. Found some references to LED issues while lurking on another thread, double checked mine, and... this thing is AWESOME. I'd been putting off replacing my TS9DX because of cost, and for $60 I ended up with a hand-built, tonally versatile BEAST of a pedal with more character and shimmer than I ever got with the 9DX. Turned out to be a pretty good birthday.

Thanks again for the help, guys!

-L

[armdnrdy]

Good!

I actually thought I saw that in the image you posted....but I thought....no....he would have oriented the LEDs the right way.....the flat side is marked on the circuit board!

Most issues come down to human error.

I would be embarrassed to offer up some of my "mistakes."  

[R O Tiree]

'Morning Liam,

Glad it's working. I've compared the layout, pics you posted, etc and it all looks good. There are 2 holes either side of that big, fat reddish-brown cap at the "north" end of the board and they are not populated on the basic layout either... but, having checked the GGG files, there is something they call the "AMZ Fat Mod" where you can put a SPST switch across those 2 holes, which shorts out that fat cap (C3) and it fattens the sound up. The other two are actually underneath D2, and they allow you to pop 2 diodes in series in that position (D2a and D2b in the mods file), so you can get assymmetric clipping, again detailed in the GGG mod file.

I'm still a tad worried about your solution, though. It shouldn't matter whether the red LEDs at D3 and D4 were both inserted 180 out - it should still have worked perfectly. If one was aligned 180 out, it would have worked... sorta... but you would have got some kind of signal. If the indicator LED was wired up bass-ackwards, then that explains why that didn't light up. I think you might have a bad GND joint or something, or maybe a GND wire was shorting the Output? Perhaps disturbing it all and popping it all back into place has sorted the problem forever and we'll never know precisely what it was. If you get any more problems with it, just gently jiggle wires, the board, etc and listen for the signal cutting in and out - you'll be able to narrow down what it is that is touching something else that it shouldn't and prevent it, or a crackly solder joint, perhaps.

All of that said, your work looks neat and tidy and all the solder joints I can see look pretty damn good for someone who describes himself as a noob. Sweet work.

On to the next project, then... what's it to be?