CaveDweller assistance needed

[Gonecat]

Hello all,
just soldered up my first Madbean circuit and having some issues.

1) Cavedweller 2015 Edition on a PCB purchased from the MBP store.

2) I hear clean guitar and when I jostle the circuit a bit I hear the echo of the circuit noise, never an echo of the guitar.  When I change the controls it does effect the delay / feedback / mix - but only of the 'circuit noise' and not of the guitar. 

With the audio probe I can track the guitar up to Pin 14.  Nothing on Pin 13.

3) I have done the following:
-Tried a different PT2399
-Triple-checked the polarity of electrolytics
-Tested voltages (below)
-Used an audio probe
-Visual inspection for crossed leads (best I could)

4) Substitutions: 
-I accidentally ordered gigantic 100v caps, but I got them in there somehow.
-My voltage regulator is the L78L05
-I strappled a 20k and a 2k resistor in parallel to get the 18k resistor

5) Voltages

PT2399 Pins:

1 - 5.07
2 - 2.62
3 - .12
4 - .12
5 - .1
6 - 2.57
7 - (no reading on my cheap multimeter)
8 - fluctuates between 0 and 4.7v
9 - 13   All measure about 2.62


Transistor:

1.52 / 0.55 / 6.23

Voltage Regulator:

9.11 / .03 / 5.1


Photos attached.  Please let me know what other info I could provide and thanks a lot for any suggestions.

[madbean]

The formula for calculating resistors in parallel is 1/R= 1/R1 + 1/R2.
With an 18k and 2k resistor you get 1/R=1/18+1/2 = 10/18 so, R=1.8k

Better to just use a 20k there.

Some of your voltages on the left side of the PT2399 are really off. Your ground is reading .1v. That's definitely not ground. Pins 7 and 8 should read between .6 and .7v.

First thing you need to do is clean up that soldering. Re-melt every joint on there and check carefully around the PT2399 for any solder bridges. Then re-measure your voltages. If you are still reading .1v on pins 3 or 4 then you've got some major ground issue. If you have a continuity checker verify your ground wires have continuity with pins 3 and 4 of the PT2399.

[midwayfair]

One leg of your LED doesn't appear to be soldered. It "grounds" pin 7 so without it your chip will definitely not function.

by the way, there's no reason to have the LED sticking up that far. You won't see it light up, and it's not an indicator. It's just to keep the chip from clipping ... through magic.

ALL your ground points are reading .1V, including the FET gate. Put your meter on continuity and check that they are all actually connected. I suspect that there is some sort of calibration error in your meter, though. If it was just one thing reading ground I would suspect something was messed up in the circuit. If it's every ground point, that suggests a meter issue. Besides, your amp would end up grounding everything even if there was a trace amount of voltage, because the amp's jack connects to earth.

[Gonecat]

Hi and thanks a lot for all the great suggestions, you two!

-removed the chip and resoldered every point on the pcb
-removed 2k resistor (duh - where's the forehead-smack icon!)
-tried both chips

I'm still getting the guitar signal coming through but now the circuit-noise echos are gone.   DRATS!

Getting continuity between ground and pins 3 and 4 (also checked other ground points on the board).

Soldered in that LED (good eye, midwayfair, thank you).  Due to the pressure of the legs, it was connecting, but its in for sure now.  I had left it with long leads in hopes of easier access to the chip, but i managed to tuck it way down in there. (I did test this LED before using it).

My meter is definitely a cheapo and i don't trust it in the milli-volt range at all.

Here are the voltages (in correct pin order this time!  i had 9-16 backwards on my first post)

1 )   5.15
2 )   2.57
3 )   .1
4 )   .1
5 )   5.15
6 )   .1
7 )   .0
8 )   4.7  (does not drift in voltage as it did before)
9 )   4.93
10 )   .64
11-16 )  2.58

[sonnyboy27]

Your chip may be locked. But I haven't messed with any pt2399 circuits yet so I can't say for sure.

You do have some solder joints along the top row in your first picture that look like they may be touching. I'd use your continuity tester to make sure you don't have anything that's accidentally making contact.

[madbean]

I don't think it's a locked chip, sonnyboy27. Voltages are still way bad.

Try this: take out the PT2399 and measure pins 3 and 4 in the socket. Do you get 0v now?

Where did you get your PT2399 from?

[Gonecat]

I got the chips from Tayda.
I did resolder all the points and test anything that looked like it might be touching with a continuity test, verifying via the schematic if they're meant to connect or not.  i also checked various other points like the pots and voltage regulator.
I'll pop the chip out tomorrow and check those pin voltages.
thanks a lot for the input

[midwayfair]

I think it's also time to start audio probing. You just need a capacitor, a cable, and a couple aligator clips. There are instructions in the tech help rules thread I think.

[Gonecat]

I did use an audio probe and as I mentioned I was able to hear the clean guitar up to pin 14.  Nothing on pin 13.

I'll try that again and see where it gets me (I am hearing clean guitar at the output, btw).


Checked voltages on pins 3 and 4 without the chip in:
With the meter set to 200m DCV I am seeing "1.2". 

[PariahBrothermann]

Paul's videos are really useful. Simple explainations and very easy to follow. Here is one of his playlists. Good resource imo. Good luck. The cavedweller is well worth getting sorted. Patience and perseverance.... Wasn't that my school motto? Best,
Toby 
https://www.youtube.com/watch?v=idWhtCU7xw0&list=PLCzwfVTc1jWQoOsBKSpfISbvTTjYtfXjp

[PariahBrothermann]

Also. The first board I ever soldered was hard work as my iron was junk. Didn't heat efficiently and just glooped the solder. Just a thought.

[Gonecat]

@PariahBrothermann:
hey thanks for the words of encouragement.  they come at a good time (!) because this is one of the last effects I have to build for my multi-effects unit that I have built into one of those early 60's suitcase turntables (with the speakers).  It's dual mono tube channels that i've (heavily) modified, and i've built about 8 other effects for it, but this is basically my first PCB build and i think my eyes and fingers just aren't as reliable with the small bits!

thanks for the link to Paul's channel - watching it now!

[PariahBrothermann]

No problem at all. I find pcb builds a lot more fiddly too, but they are definitely worth the effort, and help to support the geniuses behind them! Another thought. For smaller things, I tend to use 0.5mm solder 40/60. its a lot easier to work with. Standard 1mm for vero, etc. Lead free is a pain in the backside. Was something I discovered the hard way! Just ignore this if I'm stating the obvious, but sometimes the little things get lost in the excitement of this hobby. It's all a learning curve, but well worth it 

[PariahBrothermann]

Sounds like an epic project!

[Gonecat]

Hey Toby, yeah it is definitely a learning curve, which is something i really like!  I found the turntable (just as it was being thrown in the trash by someone) about 1.5 yrs ago and I have been slowly mod'ing it and building effects to put in place of the turntable mechanism.  What I have so far sounds really bitchin, but it just wouldn't be complete without a delay!  After this I really just have to find a cool tremolo circuit and its time to box it all up!

So, i replaced all but one or two of the gigantic .1uf caps with smaller ones i found in my stash.  Also changed out the big 2.2nf caps for 3.8nf (all i had) so that i can see if any leads are touching, etc.

At this point I have the echo back with circuit noise only. 
Clean guitar comes through, but no echo of the guitar signal.

Voltages have changed:

1 - 5.09
2 - 2.54
3 - .01
4 - .01
5 - 1.74
6 - 2.52
7 - .65
8 - ramps up to 1.02 and i hear the echo feedback start up all by itself when i touch the test lead
9 thru 16 are all 2.55v.

The stuff buzzing around in my head are:

a) Checking with the audio probe, the clean guitar comes thru on pin 14 but not 13?
b) I am getting echos of circuit noise, but not guitar.  Where should I be checking for the breakdown between the two?

Much thanks for any suggestions!