Tonepad TS808 problem

[kev93_10]

Hi, 
    I built this pedal :

http://www.tonepad.com/getFile.asp?id=81

And it worked fine. Now it doesn't.

Bypass and LED are fine but pedal mutes when on.

I checked that the board is getting power where it needs it and grounds where it needs too.

I made an audio probe and narrowed it down to pin 7 (IC1b output) and the signal is intermittent. I've replaced the IC 3 times and resoldered the pin connections.

Any thoughts/assistance.

K

[GibsonGM]

Sounds like something is shorting...check all the connections around that area, including the tone control pot.  I know you looked, but often times there is a solder bridge or cold solder joint that is almost invisible that causes these problems!! Or something touching something else and grounding a part out.  Move things around with the probe on the output, listen for crackles when turning pots, etc.  Poke wires with a pencil.  Check the switch connections for solder blobs or hanging wire ends!   

Also, read the Debugging thread and post voltages etc. if another good look doesn't produce any results. Sometimes you actually need a magnifying glass and good light.  Since it worked before, it is likely going to work again.

[Sir_Ian]

This is probably not it, and probably a dumb idea because you said you replaced the IC 3 times already.....but .....

Is your IC socketed? If not...maybe you have fried the IC every time you soldered it in. Once again....unlikely...but...felt like it might be worth saying.

What you neeed to do is read the debugging thread. Because it would help those trying to help you if we knew all the voltages, on the ic, and on the transistors. I know that when I built my TS and was having problems...by measuring the voltages...I found my problem and fixed it almost imediately. (debugging thread ---> http://www.diystompboxes.com/smfforum/index.php?topic=29816.0)

Also, check out general guitar gadgets. Their project on the Tubescreamer has some ideal voltages already listed. If yours aren't even remotely close to theirs...you have problems.

One last thing.....I'm not an expert on this stuff, but my first build was a Tubescreamer, and I had a few things I had to debug on it. The people here are very helpful...but I remember posting my question and kind of expecting someone to be like...."oh i know...its this....blah blah blah." Now that I'm trying to help you....I see why nobody came straight to the rescue. Its hard knowing whats going on in the circuit. Especially when its going wrong. BUT STICK WITH IT AND DON'T GIVE UP, YOU WILL FIND AND FIX THE PROBLEM. It might just take some time. Try going of the whole circuit with a schematic on paper and a highlighter. And Highlight every connection. When I had a problem with a my BIG MUFF, this is what I did. Sure enough....my whole schematic was highlighted to death except for one very small but important connection. 3 minutes later, with a bit of solder and heat...the problem was fixed...and I was going to bed a 4am. Then the next day I rocked out.

[kev93_10]

Thanks for the advice. I went to General Guitar Gadgets and compared their IC Pin voltages against mine and something's definitely not right :

IC Pin 1 : 3.2V (4.5V)
IC Pin 2 : 3.2V (4.5V)
IC Pin 3 : 3.1V (4.5V)
IC Pin 4 : 0V (0V)
IC Pin 5 : 0.36V (4.5V)
IC Pin 6 : 7.9V (4.5V)
IC Pin 7 : 8.3V (4.5V)
IC Pin  8 : 9V (9V)

The figures in brackets is what they get and the first number are my readings.

Can anyone tell me what would cause this?

Regards

Kev

[Zben3129]

Okay, so it worked fine, and then stopped working fine.

At this point, a couple of things are suspect. Frying parts like IC's and Transistors with a soldering iron aren't as it was working fine. However, frying them by using a 9v AC source or reverse polarity DC adapter could give you trouble.

Also, physical problem such as something shorting out, or a cold solder joint, would be my pick of what was wrong. Wires touching each other, component leads touching each other, that kind of stuff. Also, I would look at you solder joints and see if any look suspect. I would first probe around the second half of the circuit, as you said you got intermittent operation at pin 7. Intermittent operation is a big indicator of a physical problem, aswell.



Then, you replaced the IC.

If the IC isn't socketed, then frying it with a soldering iron is very likely. If you were trying to make sure you had a good solder joint at pin 7, you may have overheated the IC and killed it.



I would say start by socketing the IC if it isn't already (please let us know this info).
After you do that put in a new battery if possible
Then, get some new voltages and post them here. The voltages are definitely bad as they are right now, and we need to find the cause.



Zach

[kev93_10]

The IC is socketed. It always has been. Apologies for not stating this earlier.

I'll do the rest of your suggestions tomorrow and let you know. It's getting late here (UK) so I won't do anything tonight.

Regards

Kev

[Zben3129]

Okay, one more quick question, when you reflowed the joints did you have the chip in the socket?

[kev93_10]

Nope.

Took the IC out, for the reasons mentioned above.

K

[ACS]

I had a vaguely similar problem with a Rat - in this case it was a crappy socket that was making good contact with the IC.  Unlikely, but worth a look...

[Zben3129]

does the battery get hot?

[kev93_10]

No it doesn't, but I don't use a battery, I use a PSU. And that doesn't get hot?!

Tried everything else mentioned above and it's still not working.

Something strange did happen though :

I had an audio probe at the output and I was poking around as per the notes above and a low level signal slowly built up and started getting through. Then it stopped? It built up gradually then stopped?

K

[Zben3129]

Sounds like a cap problem.

Could you probe just before the 10uf cap on the output, on the wiper of the volume pot, and just after the 1uf NP in the second half of the circuit?

Zach

[kev93_10]

Probed at all of the above points and got nothing.

Pin 7 probe still gives nothing and all the points you mentioned were after that.

K

[Zben3129]

Well I guess what is confusing me is that you said you probed on the output and got a weak signal that grew and then shut off. You are talking guitar signal, right, not just noise?

Zach

[kev93_10]

No - Talking about noise.

There was nothing then there was something building up - but not a normal guitar signal.

I'm still confused about the IC pin voltages. How can I sort that out?

K

[kev93_10]

Anyone got any thoughts?

Ta

K