Pedal Builders - do you have a particular sequence/method for trouble shooting?

DannyP

Hi all,

 

I've built my first couple of pedals and one works fine, but the other is intermittent.

 

I'm no electronics expert, but I'm keen to learn and I'm trying to learn-by-doing. However, if you follow the instructions and it all works fine, you don't really learn anything - which is what I found with my Ampmaker build a couple of years ago.

I've been looking at various things on youtube to try to help me with this intermittent pedal. I put together an audio probe and have traced the signal back to a particular place, but the component there seems to be working.

I have a DMM and so I've been checking continuity and voltage of various bits and bobs, but I don't really know what I'm doing or how to interpret my findings.

Do any builders have a specific method such:

Does pedal work Y or N: N

Does this bit do what it should Y or N:

Have we tested this Y or N:

Is the reading for X correct Y or N:

etc etc etc...

 

 

Or one of those cloud charty things - if you know what I mean?

 

Any help extremely gratefully received.

 

Ta

 

DannyP

 

Maxi

What pedal is it ? is it a kit on pcb or are you fabricating your own? 

Two main areas of error are component value (the decimal point on caps)  and incomplete circuit or wrong way round components.

1. Check component list and location .

2. check traces jumpers and wire .

3. pots and wiring .

You can save a shed load of debugging by quickly checking tolerances before populating the board .

ThePrettyDamned

When my fuzz was intermittent (bear in mind it's a bloody birdsnest!) it was just the PCB grounding against the chassis.  

Assuming you have ensured that is not happening (so the signal isn't being grounded somewhere), follow what maxi said.  

Maxi

Ha I didnt think of that .

Intermittent ....the 1st thing I would go thru would be off board mechanical bits .

Cirrus

When I built my first pedal my method was as follows:

1. Is pedal working? No.

2. Do you know what you did wrong? No, except on an overarching level my mistake was trying to build a pedal.

3. What are you going to do now? Give up.

4. Are you sure? Yes.

5. What about this wire? This one right here that's not connected at one end? Oh, I didn't see that...

6. Are you going to solder it in? Yeah, I guess so.

7. Does it work now? Yes.

DannyP

Cheers for the replies chaps.

It's a Hotcake clone from the Poodle.

 

When I first builded it, it worked fine until I closed the enclosure, at which point it cut out - bypass was fine but it had become a killswitch.

I covered the interior of the enclosure base with insulation tape - still intermittent.

I experimented with pieces of foam above and below the pcb - still intermittent.

During this period of experimentation, the pedal would often come back to life when I brushed the underside of the board with my fingers by accident - usually around the bigger caps.?.?.?

I disconnected the 9v and Ground wires and flipped the board over (originally the components were facing down towards the base, now they face up towards the pots, which it should have been in the first place I guess - inexperience).

In doing this, I bolloxed up part of the copper track where the 9v connects to the boards, so I ended up wiring the 9v directly to the first resistor in circuit (plus I needed to take the resistor going to the LED off the board, no biggy).

I boxed it up again and it worked fine and sounded great for about 2 days.

Then it died again.

Then I noticed it was making some weird, clipped noises when I strummed really really hard, so I opened it up and it popped back into life. Then died again. Then I wiggled the board and brushed some of the connections under the board with my finger and it came back to life. Then I closed the enclosure and it died. Then after a bit it started working - you get the picture....

I’m trying to teach myself to be self-sufficient in trouble shooting, so I put together an audio probe with the aid of youtube.

 

At such time as it's dead, I can track a faint audio signal back from the Board Out, via Vol Pot, C8, Pres Pot, C7, R10, C6, R6, R7 to leg 6 of the IC1.

 

I then get nothing from the other side of the IC1 (leg 2 or 3 or any components prior).

 

Brilliant! I’ve got another chip I can try!

 

Alas, no. Doesn’t work with either one. I can’t see any solder bridges or board damage around that area.

 

I'm just a bit stuck really - it sounded bloody great when it actually worked!

 

ThePrettyDamned

If it was fine pre-enclosure, it's either the switch wired wrong, or it's grounding against the enclosure.  I had a crude method to prevent this - I just used electrical tape to insulate the back of the enclosure on the inside.  Problem solved.

I'd say there is something wrong though, if the enclosure is already masked...

DannyP

Yeah, it's  neither of those things. Frustrating!

Misterg

This is a 'Chilly biscuit', right?  If so, you're trying to trace the signal backwards - pin 6 is the output of the chip, not the input.

I would suggest the generic sequence runs something like:

0) Try a new battery

1) Check power & ground voltages are making it to the board and to the supply and ground (or -ve supply) pins of any chips (measure at the chip with both meter probes, or you won't find missing ground connections - how do I know...?);

2) Check any internal '0V' supplies (the junction of R3, R4 & C2 on your circuit) - should be somewhere close to 1/2 of the supply voltage;

3) Measure C, B & E voltages of any transistors (not relevant here) - B should be ~0.6V different to  E

4) Measure the voltages of '-' and '+' inputs of any op-amps (pins 2 and 3 of your chip) which should be the same as each other and close to the voltage measured in (2)

5) Measure the voltage at the outputs of any op-amps (pin 6 of your chip). If the voltages in (4) are as expected, then the output should also be fairly close to the voltage measured in (2)

For most simple pedal circuits, that will establish that the electronics are basically functional - if anything is out of line, look for the cause of that problem.

If it checks out, it's likely that the signal isn't making it to the board, or isn't making it back again, or there is a wiring mistake / missing component / etc.

Unfortunately intermittent stuff like that is 99.9% of the time something 'mechanical' - a poor solder joint, cracked PCB track, whisker of wire touching, or something shorting out. As such, I think you're most likely to find it by mechanical means - check over all the solder joints with a magnifying glass, make sure that nothing is shorting out - especially whiskers of wire on the interconnecting wires. You may be able to localise the fault by tapping things - if you can make the fault come and go by tapping a certain area of the board, then you've narrowed the search down.

Stuff that's not so easy is bad contacts on jack socket switches or dead foot switches.

HTH

DannyP

Thanks MisterG, have a wisdom.

You're quite right, it's a Chilly Biscuit.

I've done a few of those steps, but there's plenty of homework to be getting on with there, I'll see how I get on.....

NervousJohn

What solder did you use? If its lead free, you need a bit more heat in your iron to make it flow. That in turn results in dry joints, especially as your building your solder skills.

Type "solder dry joint" into google images and look for something similar.

DannyP

Ok cheers John, shall do.

randomhandclaps

Having read all you put I would bet that the issue is a dodgy solder on one of the wires to the board or on the pots.  When things are wriggled around it's incredibly easy to stress iffy joints.

Can you post any photos?

Maxi

trying to find a link to the board or kit any one got it?

Hey Danny care to post some pics of yours also ?

Misterg

Board, etc. is in a pdf file here:

http://pedalparts.co.uk/wp-content/uploads/2013/08/ChillyBiscuit.pdf

(Or on the 'Chilly Biscuit' link here:

http://pedalparts.co.uk/category/diagrams/

if the link to the pdf doesn't work!)

DannyP

Thanks for the comments, lads.

I'm just going to be looking after the kids for a few hours, but I'll be back on later with pics and details.

(also I don't seem to be able to click 'Wisdoms' at the mo, but I'll dole them out later if it starts working again!)

juansolo

My debugging routine:

- My eyesight ain't what it used to be so the first thing I look for are solder bridges with a magnifying glass.

- Then I get annoyed when I can't find them as it means I've f**ked up elsewhere so hand it to Cleggy to stare at. To double check that I've not got a resistor wrong or a diode in backwards. After you've been staring at a board as you're making it, you tend not to be able to see mistakes for looking.

- Take a break. It's a really good idea. Last time I did this I decided to debug it the following day. I got home, looked at the layout on my computer and the jumper I'd missed was staring me in the face.

- Check voltages to make sure everything is getting something like it should.

- Audio probe it to find where the signal stops. This usually finds where the issue is.

- At this point if we've still not found the issue, it'll end up in the box of shame (staging area for the bin).

Builds are usually tested before they're boxed up, so if it goes in the box and doesn't work, 9 times out of 10 something is shorting.

Maxi

check the sensitive components on the board for over heating during the solder process . Those polybox caps sometimes melt thru something metallic to the outside if over heated and start to fail . The diode can fail if over heated with iron too .I dont know if an intermittent fault would result but its worth a look . other than that no real obvious area on the board to check unless an electro cap is round the wrong way ...

It looks like a pretty bullet proof straight forward layout . You cant really test the caps in circuit properly but you can test the diode. The audio probe will show where the signal drops off the most so that would give you a clue to what replacement you'll need .

Its the postman that slows us down

DannyP

 OK here's some pics.

I tried 'resoldering' anything that looked even slightly dull - resulting in the board looking a bit messier than before.

For a while, wiggling C3 seemed to bring it back to life, so I heated the legs and whacked a bit more solder on the joints - now it doesn't seem to work at all!

When it was working, it worked perfectly - great sound, pots did what they were supposed to - but when it cuts out, that's it.

Getting a bit sad about the whole enterprise now

DannyP

 

 

http://i611.photobucket.com/albums/tt192/p1eces/chilly3.jpg

 

DannyP

http://i611.photobucket.com/albums/tt192/p1eces/chilly1.jpg