Another pedal another problem

[RobA]

Sometimes my testing rig goes stupid on me too.

Sometimes I go stupid on me  . That's when it gets really fun debugging.

[jimilee]

 

[RobA]

...

One question about the solder joints, are you using lead free solder?

Yes I am. I was using leaded stuff and started to get a tight chest so switched to lead free some time ago. I bought a much better soldering iron yesterday and did some work on another board last night at 400C/750F. Is that going to be hot enough to get nice solder joints with lead free?

400 should be good. Different lead free solders behave differently, so that's a bit of a learning process too. I'm still working on figuring what works best here too. I just got a new lead free solder that I hope to test this week. It is a bit more challenging to work with the lead free, but I think it is worth it.

It would be a good idea to check the voltages on the power pins of the chips and the regulator to see where you are at.

Will do. Where can I find what the voltages of the IC should be? I can't see them on the schematic.

Sorry for all the questions. I've only built 3 relatively simple pedals before and I'm encountering a lot of 'firsts' with this build. There's always more to learn!

No problem with the questions, it's what this section of the forum is all about.

Good question on the voltages. You usually need to take them from a known working pedal. Good circular catch there huh? (Really you could work it out theoretically or simulate it, but that's going to be a pain.) But, for the supply voltages, which is where you need to start, you can see it on the schematic. Mainly you want to look at the voltage on the regulator, LM386, and PT2399 to start. Pin 3 of the regulator should be close to 5 volts which feeds pin 1 of the PT2399 and this should be at 5 volts too. Pin 6 of the LM386 should be close to 9V (whatever is at pin 1 of the regulator and the output of D1). It should really be at about 0.6V less than your input voltage.

[Guybrush]

Thank you so much.

Is this the correct method to test voltages:

- Hook circuit up to test rig and power up.
- Clip or hold black DMM probe onto ground wire.
- Touch red DMM probe to point on circuit that needs to be tested.
- Take reading.

Will the reading settle and be definate or may it wander a little?

Thanks

[RobA]

Yep, that would be the process.

The reading stability depends on the pedal. Some can wander or pulse if there is an element that changes how much power it draws (like LED's in an LFO based circuit). Sometimes the voltage on a pin will move quite a bit as in the pins on IC's in an LFO.

I guessing that these power supply pins should be pretty stable.

[Guybrush]

I've got home re-flowed all the joints and it's working perfectly.

Thank you for everyone's help. I may not have had to use all the advice given but I've learnt tonnes from all your help.

Hi-5s all round.

Time to start on the mods now!

Cheers guys!

[RobA]

Excellent! Congrats on the build.

[jimilee]

Awesome feeling

[Guybrush]

Spoke to soon...
I was playing around with it on my test rig and it just stopped working.
I'm getting sound but no effect. Theinternal LED isn't lighting at all and the knobs aren't working. Ha.

EDIT:

I tool some voltage readings. They don't mean much to me but could anyone please tell me if they look correct?

Regulator:
1: 8.56
2: 0.03
3: 4.8

IC1:
1: 1.34
2: 10.2
3: 0.02
4: 0.02
5: 3.92
6: 8.57
7: 4.27
8: 1.35

IC2:
1: 4.78
2: 2.39
3: 0.05
4: 0.05
5: 0.00
6: 0.01
7: 0.27
8: 0.39
9: 2.39
10: 2.39
11: 2.39
12: 2.39
13: 2.39
14: 2.38
15: 2.39
16: 2.39

Phew.

[RobA]

Well that sucks. But, look at it this way, you'll be able to celebrate getting it fixed twice now.

The good thing is that you know the LM386 is good and that the audio path is good from there to the output.

Is the blend knob working like a volume pot?

One thing to note is that the LED is tuned on by the guitar signal from the LM386. It could be very faint and still be doing it's job.

Go back to checking the voltages at the PT2399 and then trace the audio at pins 16 15 14 13 and around R5. Then listen at lug 3 of the blend pot and trace back from there to the PT2399.

I'm assuming that you still should get delayed audio even if the LED/LDR aren't working. So you should focus on the PT2399 first. If I'm wrong about that, hopefully someone will let us know.

[Govmnt_Lacky]

Im no master builder BUT...

How can you have a higher voltage (10.2) on Pin 2 of IC1 than you have going into the pedal/circuit 

I'd say you have something going on in that area 

[RobA]

Are you sure that pin 2 reading wasn't in mV?

[RobA]

The one that really stands out to me is pin 6 on the PT2399. Does this vary at all when you move the depth or delay pots? I would use my DMM to check and see if pin 6 has continuity to ground.

[Guybrush]

I re-checked and some of the voltages were the same and some were different. I had a dig in my parts box and found I had a spare of each chip. I swapped them both out and hey-presto all's well again! Perfectly screwed up delay goodness.

Fingers crossed that'll be the end of it!

Thanks again!

[RobA]

Well Yeah! again . It is very likely that the earlier voltage problems caused problems for the PT2399. I'd guess the LM86 might be good though and I'd test it in the circuit to see.