ROG Thunderbird Issues After Boxing

[debrad]

Hi everyone,

I recently posted this on another board but was hoping some of you might have some suggestions for me...

Last week I completed a Runoffgroove "Thunderbird" using the 1776 PCB and it worked great and sounded phenomenal on my test rig but has not worked properly since boxing it in the final enclosure.  Based on the debugging sticky, done my best to take as many measurements as I can think of and will post them below along with other details in hopes that someone might be able to help me get this sounding as good "in the box" as it did "out of the box".

Note that I made 2 small deviations from the original...1) I used a 3k9 resistor instead of the 3k3 for R26 but that didn't seem to be an issue on the test rig...and 2) I jumpered the "E" and "C" pins of Q1 as outlined as an option on the Runoffgroove site (I also left out R35 to ensure there wasn't any path to the board's "R" pin).

As wired, the bypass signal is fine.  When the effect is switched "on", there is very little volume and very little gain...both of these controls must be FULLY clockwise to get volume over unity and there is just a mild overdriven sound.  Cranking the Tone, Bottom, and Presence controls to full CW provides a little more volume and gain; however the tone is VERY bright and harsh.  I also notice that pushing and pulling vertically on the Bottom potentiometer adds and removes signal from a talk radio channel.

Using an audio probe on the circuit shows audio on all 3 pins of the potentiometers regardless of position.  I also hear audio on the input and output jack leads AND the ground leads and most of the IC pins but didn't note the specific details of the ICs when I was audio probing them; however, I do know there was nothing but a wash of noise on Pin 1 of IC3.

Tonight I took the time to take as many voltage measurements as I could and hope the following will be helpful:

@ DC jack = 9.11v
@ input pin of PCB = 9.11v

@ collector of Q1 = 8.78v

@ IC4......Pin1 = 8.78v                   Pin5 = 0.00v
               Pin2 = 4.43v                   Pin6 = 2.55v
               Pin3 = 0.00v                   Pin7 = 1.46v
               Pin4 = 0.00v                   Pin8 = 8.78v

@ "+" pin of C35 = 4.43v

@ D10 = 8.78 (anode)...12.75 (cathode)
@ D11 = 12.75 (anode)...16.48 (cathode)
@ D12 = 16.47 (anode)...20.3 (cathode)
@ D13 = 20.3 (anode)...24.1 (cathode)

@ IC1.....Pin1 = 11.6v          Pin5 = 10.5v
              Pin2 = 11.6v          Pin6 = 11.6v
              Pin3 = 10.6v          Pin7 = 11.6v
              Pin4 = 0.00v          Pin8 = 22.9v

@ "+" of C29 = 22.9v

@ IC2.....Pin1 = 11.4v          Pin5 = 11.4v
              Pin2 = 11.4v          Pin6 = 11.5v
              Pin3 = 11.4v          Pin7 = 11.4v
              Pin4 = 0.00v          Pin8 = 22.9v

@ "+" of C30 = 22.9v

@ IC3.....Pin1 = 22.1v          Pin5 = 11.4v
              Pin2 = 21.2v          Pin6 = 11.4v
              Pin3 = 3.5v            Pin7 = 11.4v
              Pin4 = 0.0v            Pin8 = 22.9v

@ D7 and D8...0v at both anode and cathode
@ D5 and D6...0v at both anode and cathode

@ D3 = 21.2v (anode) and 22.1v (cathode)
@ D4 = 22.1v (anode) and 21.2v (cathode)

@ C35 = 12.7v (a) and 4.4v (c)
@ C36 = 16.4v (a) and 0.0v (c)
@ C37 = 20.4v (a) and 4.4v (c)
@ C38 = 24.1v (a) and 0.0v (c)

@ Tone, Gain, and Level potentiometers = 0.0v on all 3 pins regardless of position
@ Bottom, Top, and Presence potentiometers= 11.4v on all 3 pins regardless of position

@ indicator LED (3mm red LED with 4.7k resistor on cathode)
    .....9.1v (anode) and 7.6V cathode in bypass
    .....1.9v (anode) and 0.0v cathode when effect is on

I have also taken a photo of the boxed PCB in case you can see any issues I may have missed:



I look forward to your replies and thank you in advance for any suggestions and/or advice you might have for me!

- brad -

[GibsonGM]

Hi Debrad...

#1    Unbox it...see if it still works ok!    If not, and it worked before....did you add the switches and jacks etc AFTER you tried it out?    Trouble often lies in the connections made last, the things I just listed.      You could have a short between lugs of a stomp switch, for instance.   Or something under the board touching the enclosure....

Look closely at the 9V adapter to be sure it's wired right, too.

Observation:  If you have NOTHING connecting your enclosure to ground (insulated jacks there?), you need to find a way to do that, to make the enclosure shield your effect!  Skip if one of your jacks is in fact doing this....

Thanks for the detailed voltages...I'm not familiar w/the thunderbird and not sure offhand what they should be due to the "other chip" and charge pump...someone will come along to tell you, I am sure.   Altho, if something is shorting, the numbers might not mean much right now....

[debrad]

Thanks GibsonGM!

Doing a TRUE unboxing was going to be one of my next steps (I did try undoing the control nuts and lifted the PCB to see if it might be grounding on the enclosure but all the off-board wiring was still intact and it wound up being more awkward than useful).  For the first time, I was actually happy with my off-board wiring on this one so I'm afraid I'll have to resign myself to de-soldering...

The jacks DO ground on the enclosure so I don't think that should be an issue.  In terms of grounding though, I was a LITTLE unsure whether I should run the PCB ground direct to one of the jack grounds or to the ground/"negative centre" lug of the DC jack but most instructions seemed to show the latter so I went that route (and ran a ground from the DC ground/"negative centre" to the input jack ground).  Hopefully that is OK...

As for the voltages...I can see how the values might not mean much to you if you aren't familiar with the specific circuit.  What I can tell you is that my IC1, IC2, and IC4 voltages are pretty close to the 1776 values (maybe 1v less here and there); however, Pin1 and Pin2 of my IC3 are almost double what's shown in the 1776 build documents (22.1v (Pin1) and 21.2v (Pin2) on my build rather than 1776's 11.95v and 12.04v respectively) and my IC3 Pin3 value (3.5v) is about 1/4 of the 12.04v in the 1776 document.

[GibsonGM]

Hi brad, gnd is probably ok that way.  I personally run them to the switching jack (input jack)...I connect board grounds to one tab and the other goes to battery minus, but that is irrelevant - I don't like going to the DC jack since the tabs are small!  lol     I physically connect output jack gnd (sleeve) back to that point too, in case the nut comes loose (!) on stage, which will make it go "BRRRRRRRRR"...

I did think the IC voltages there looked HIGH.   What can happen when you box things is that the circuit may touch the enclosure and short something...or a piece of wire, solder etc. can fall in and bridge pads.  Neither are good    So scan that area with a magnifying glass!

I'd unbox and try it...and look at those voltages again if it is not ok.   

Of course you'll need to trace every in/out wire, making SURE you have tip to input and not sleeve to input, etc etc...go thru the switch connections, and so on.    No need to desolder first.   Pot  backs and tabs can also hit places they should not, if not "in" the PCB.      I put rubber foam under my PCBs...non conductive packing stuff.

This gets faster/easier as you go along, so no worries.  In the future it will take you 15 minutes to solve this kinda thing! 

[Ben Lyman]

You got GibsonGM on the case so I am sure you will get it sorted but here's a couple ideas anyway.
Looks like a "no battery" effect right?

So make sure you wired the DC jack correctly, you can even run the two +9v terminals together... just to make sure juice is going to the board.

You also need that DC jack ground terminal from the board ground to have another wire that goes to the box and jacks etc ground, you know, bring it all together.
It looks like you have but I can't tell for sure.

If you are using a 3 or 4 lug jack for either the in or the out (usually the in with a battery) anyway, make sure you are linking your grounds to the right lug... or since you are not (?) installing a battery clip... just go ahead and link the lugs... bring all the grounds together (unless there will be a battery clip involved)

[debrad]

Thanks for the additional replies...MUCH appreciated!

I've set this build up for "no-battery" and right now my board ground goes to the DC jack "-" lug which, in turn, ALSO connects to the ground lug on the mono input jack so I think that part is OK (of course, I will double check those connections again to make sure).  I also have a ground wire running from the 3PDT switch to the ground lug of the mono output jack and that output jack ground is connected to the input jack ground by a wire AND the metal enclosure.

My control pots are also board mounted so they SHOULD be OK.  Two things make me nervous with the potentiometers though:

the first being the 11.4v I'm measuring on the "tone" controls (i.e. tone, top, bottom, presence") - does it make sense to be measuring voltage on their 3 lugs?  to be measuring as much as 11.4v on those lugs?  and, if so, to be measuring the 11.4v on all three lugs of all three controls regardless of their position?

the second being the fact that the "bottom" potentiometer appears to have some vertical play and, when it moves up and down, it passes and/or stops passing radio frequencies (depending on position).  From what I can tell, the play is just the tabs moving up and down in the tab slots on the PCB.  I also notice that the  "bottom" pot appears to have an "active" area near the middle of the sweep where the tone changes; however, to the CW and CCW sweeps of this small range, nothing really happens and the tone seems to stay the same.

Both of these issues make me wonder if the either the "bottom" pot might be messed up influencing the rest of the circuit or if therre is another component that might be messed up and allowing voltage (or TOO MUCH voltage) to enter the tone controls?

Regardless, I am just about to pull the PCB from the enclosure so I will  see if anything improves once I've done that and connected to my test rig.

[debrad]

Me again...

After unboxing the PCB and looking closely, I *THOUGHT* I had found the smoking gun...a hair thickness strand of wire shorting the cathodes of C34 and D9 (held in place by nothing but static cling!).  Unfortunately, removing the strand didn't solve anything.

Next I reflowed ALL of my solder connections...no change.

Next I replaced a suspicious looking 22nf cap...no change.

As I typed a reply to Brian at Runoffgroove (he has kindly been very patient, acommodating, and helpful), something finally hit me:

What I realized is that the Pin1 and Pin2 voltages of IC3 (22.1v and 21.2v respectively) are the same as the values measured at the anodes and cathodes of diodes 3 and 4 (the two green LEDs that lie in the path of Pin1 and Pin2 of IC3 in the 1776 layout).  What I had also noticed from the beginning of this debugging adventure is that when I probe Pin3 of IC3 with the volt meter, one LED momentarily lights up when I put the lead on Pin3 and the other LED momentarily lights up when I take the lead off Pin3.  I suspect this is NOT a coincidence...

Is there any chance this is symptomatic of the LEDs being wired backwards?  If not, does anything else come to mind that might create this scenario?

[Ben Lyman]

Is there any chance U4 pins 3&5 are touching a ground?
Just a WAG as i don't know if they are supposed to be 0v.
Maybe they are shorted to pin 4 or something

[debrad]

Is there any chance U4 pins 3&5 are touching a ground?
Just a WAG as i don't know if they are supposed to be 0v.
Maybe they are shorted to pin 4 or something

According to the 1776 build documents, U4 pins 3, 4 and 5 should all read 0.0v

[antonis]

@ D10 = 8.78 (anode)...12.75 (cathode)
@ D11 = 12.75 (anode)...16.48 (cathode)
@ D12 = 16.47 (anode)...20.3 (cathode)
@ D13 = 20.3 (anode)...24.1 (cathode)

I don't know the role of these diodes in your circuit but as you've wrote it they should have about 4V reverse voltage drop...

[sajy_ho]

I have always the same problem with 1771 PCBs, and the reason for the issue is always a short in the PCB!
I think 1776 PCB tracks may be a little too much compact, at least for me 
Anyway; using an audio probe and tracing the signal path from the input jack helped me to identify the problem all the time.

[debrad]

I don't know the role of these diodes in your circuit but as you've wrote it they should have about 4V reverse voltage drop...

Just to clarify...are you saying they are functioning properly or should the higher voltages be on the anode (non-striped) side of these diodes (if it is any help, I have posted the schematic below...something I probably should have done from the start - sorry!):

NOTE that IC3 pins 1, 2 and 3, on the 1776 PCB (where I note voltage differences) appears to actually be "U2b" on the schematic (i.e. the section tied to the green LEDs)...

[debrad]

I have always the same problem with 1771 PCBs, and the reason for the issue is always a short in the PCB!
I think 1776 PCB tracks may be a little too much compact, at least for me 
Anyway; using an audio probe and tracing the signal path from the input jack helped me to identify the problem all the time.

This makes me a little nervous!  I actually put together a test rig (including an audio probe) just before starting the Thunderbird project but I have to admit that my audio probing experience is rather limited so that, combined with my limited skills with schematics will make this a slow go!  Having said that, both are skills I am eager to improve so...no time like the present.

What I did notice from the bit of audio probing I did with this project last week, it's a little more difficult to find that "smoking gun" when the faulty effect is actually passing signal.  With zero output, you can probe along until the audio disappears; however, I'm not 100% sure what to listen for when the audio is making it all the way to the output but just not doing so with the kind of volume and/or tone I'm expecting (especially when it seems to be winding up on ground as well!).

[debrad]

Great news everybody!

When I shared the details of the IC3 voltage differences with Josh at 1776, he suggested a closer inspection of the "VR Net" for IC3 which might explain the low voltage on pin3.

By highlighting that section, he enabled me to QUICKLY zero in on a small razor thin slice in the trace running between pin3 and R34 that I must have nicked when I was removing the centre socket of Q1.  When I double checked, there was no connectivity between pin3 and R34 so I checked the slice and ground and sure enough, it was shorting.

By cleaning up the cut, I was able to eliminate the short which restored the proper connectivity so that a quick test on my test rig sounded just like I had remembered it originally.

I dropped a small bead of clear nail polish over the slice to keep anything else from getting in there, re-tested and everything was working great so I went ahead and boxed it up. I still have some noise in the circuit but, from what I understand, that is probably due to the high gain structure of the pedal so I am VERY happy!

- brad -

[chuckd666]

Yeah I made a PCB from the layout on the ROG site. My questionable PCB quality aside, the effect sounds great, though it is inherently noisy. Well, has a low level hiss. Damn it sounds like an amp though.

[Ben Lyman]

Sweet!
                                                                                                                                                                                                                                                           

[antonis]

Just to clarify...are you saying they are functioning properly or should the higher voltages be on the anode (non-striped) side of these diodes (if it is any help, I have posted the schematic below...something I probably should have done from the start - sorry!):

<should the higher voltages be on the anode (non-striped) side of these diodes.?>
Yeapppp..

Allthough your scheme doesn't include parts numbering, I can't see any kind of diode (Schottky, Si or LED) which has a 4V forward voltage drop..
(according to your measurements..)

[debrad]

I have to admit that I don't understand a lot about the design of this circuit but, now that I fixed up that short, it is doing exactly what it's supposed to do!

Here is the final assembly...ready to rock!!!

[GibsonGM]

Very nice, man!

[debrad]

Very nice, man!

Appreciate it!  I'd be lost without all the help and knowledge passed along by kind folks like you and the rest of the DIY pedal community.  Love the fact that I literally learn something new every day in this world!