OCD and ROG Umble debug help.

[skibum1999]

I need help with 2 pedals please. First is OCD, just powered it up today, and i can't measure the voltages because its ruining my batteries  . I made a substitution (1n4148 for 1n34a) and the pedal bypasses properly, but the LED won't light up and all i get is a soft hiss when the effect is engaged. I think the problem might be a solder bridge between the positive and negative leads of C5.

Also the Umble. I've been hacking away at this one for awhile, can't seem to get it to work. The LED works properly, the effect bypasses properly, but no sound comes through the effect when engaged. Q1, Q2, and Q4 are getting proper 4.5v but Q3 is getting nothing. Might be a bad trimpot, as my first one exploded, but now has been replaced. Could be a bad trace as well.

Thank you VERY  much to anyone who helps. For reference, the OCD i used is here http://s197.photobucket.com/albums/aa131/veroboard/Commercial/Fulltone/OCD/?action=view&current=ocd_vero_debug.png

Umble
http://www.olcircuits.com/olc_umble_buildguide.pdf

Thanks!

[Zben3129]

Could you test the resistance across c5? If you have a solder bridge, it will read 0 ohms or something really low. You don't need a battery in to do this, either.

If a pedal is ruining batteries (battery heats up real bad and dies quickly?), then you almost always have a direct short between +9v and ground somewhere. In this case, solder bridge across c5 would connect 9v and ground.


Good Luck! I'll take a look at the Umble stuff in a minute, gotta eat lunch right now.

Zach

[Zben3129]

Reguarding Umble:

Measure resistance across the trimpot, and see what you get. Also, measure the resistance across the other trimmers on the working transistors and let me know what you get for each one.

Zach

[skibum1999]

Hey thanks for all the help. For the OCD, the solder bridge has 0 resistance so that must be the problem. As for the umble, the trimpots are reading about 13.3k ohms, but the bad pot has a 0 reading. Again, i really appreciate your time.

[Zben3129]

No problem, glad you found the problems. Fix the solder bridge, replace the trimpot and you will (hopefully) be in buisness! The only other concern i have is that there may be an issue with the circuit around the trimpot, as 2 bad trimmers is not exactly likely. If you put in a new one and it blows again that may be the case, and if it works then you just got unlucky 

Zach

[skibum1999]

ahhh i fixed the solder bridge but it appears that wasn't the problem. Could it be a trace cut? Also, i forgot to mention that i used a tl072 not a tl082

[Zben3129]

Does it still kill the battery or does it just not pass audio now?

[Zben3129]

Could you take a measurement of the resistance between ground and 9v, and then 9v and ground. (one test with red lead on 9v and one test with red lead on ground)

If you have the diode installed backwards, then red lead on ground test will show 0 ohms and the other test will show nothing, or a very very high reading.

If you have a solder bridge somewhere else between 9v and ground, then both tests will show 0 ohms.



Zach

[skibum1999]

still kills the battery. I will try your recommendation

[skibum1999]

both tests show 0 ohms

[Zben3129]

Alright. This means you still have a short from 9v to ground.

Check to make sure that D1 is oriented properly.

Check for solder bridge across C7.

Check to make sure the trace cuts in rows 5 and 9 are complete.


Good luck

Zach

[skibum1999]

ok i checked d1, trace cuts, c7, nothing wrong. i think it could be another solder bridge where the ground pcb wire is. ill try that