Tried to mod DOD250 and now get a loud buzzing...and other problems.

[alphadog808]

Hi guys,
   1st post here, I'm hoping you guys can help me, I suspect my problem isn't too complicated, but I don't know what's happening.

I have a DOD OD250 that came with a LED and true bypass.  It worked.  Yay! 

I then got a mod kit that changes out components to bring it back to original specs AND change out a the DOD power connector to a Boss style power connector.  THAT is where I got into trouble.

After every component change(except the power part) I did a quick audio test to make sure it was working. It was.  Last step was the power connector change.  After doing the soldering, I checked, and checked, and rechecked as I wanted to make sure I didn't screw stuff up. 

Plugged in the power...bypass works, but when I turn on the pedal, I get a loud buzzing.  When I turn the level and gain, I hear audio changes, sometimes it sounds like a whine that is reminiscent of the movies when they are trying to tune in a radio station.  I can faintly hear the guitar in the background.

I put in the 9volt battery to see if that made a difference, and I get the same audio problems.  But, I also noticed that the LED didn't come on. It seems it only comes on with the wall wart power.

I checked connections, reflowed, and even removed diodes D1 and D2 in hopes that maybe I blew something up.  No dice. I thought I had read that one of those diodes was protection in case I reversed polarity.

Checked the boss connector, and it seems ok.  Tested with a multimeter. 

With all that being said, I think I'm stuck.  I'm wondering if maybe a component is fried?  Maybe the IC?  I don't know much about electronics...I was going to put in the original IC unless you guys think there are some other components to check?  What also concerns me is the LED only working with the wall wort but not the battery.  As far as I can tell, it's pretty much the same circuit as what the wall wart is passing.  Any ideas where to start troubleshooting? 

Here is a post that has the schematic of the board...
http://www.diystompboxes.com/smfforum/index.php?topic=84918.0

Thanks so much in advance!! 

[aron]

Not sure what the mod entails for power, but it's probably a wiring problem or perhaps a bad solder joint that is bridging two (or more) traces. Check again.

[alphadog808]

Hey Aron,
  Thanks for getting back to me!  I really appreciate it.

The power mod isn't anything special, its supposed to convert the DOD power socket to a boss style socket.  The Boss socket has 3 connections; from what I can tell
- one is the pin, it's -. Goes to a connection on either the input or output.(I forget). Also goes to a white wire which then goes to the pcb.
- one goes to the battery, +.
- one goes to a resistor then LED.  Also goes to a light green wire that then goes to the pcb

Note, I might a little off, I'm doing this by memory, don't have the pedal with me.

From what I can tell, the socket bridges the 2nd and 3rd connections.  When you plug in the barrel connector, it cuts connection 2 as you don't need the battery, only the wall wort.  the 1st pin is always on.  Seems pretty standard, and my multimeter seems to confirm that it's working ok.  I'll double check tho.

Note, the wiring was working before, and I reflowed all the solder points. I'll double check for joints bridging traces.

Any idea why the LED wouldn't work on the battery but does on the wall wort?

I'll try to upload some pics of the pedal in a bit.

[alphadog808]

Here's some pics...don't know how helpful they will be.  I'll try to take some of the pcb tonight as well.

[Paul Marossy]

Are you sure that you didn't mix up the polarity on the DC jack? IIRC, when I had a couple of DOD pedals a long time ago, the 1/8" DC jacks were center positive and I know for sure that Boss pedals are center negative...

[alphadog808]

Hey Paul, I'm not sure, to be honest.  I was just following the instructions I got from the the monte allums kit.  

But that being said, if it was wrong, I don't know how I'd get around that as I need 2 connections for +, one for the battery and one for the wall wart, correct?  Not sure how I'd wire it opposite and get the same effect(where the battery disconnects when you plug in the wall wart).  As you can tell, I'm not the best electrical engineer..

Assuming it is wired opposite, should I expect to see some fried components?  If I were to switch wiring, and it was NOT a good thing to do, would I fry anything?  Note, I took out D1 and D2, but can put them back, if needed.

Oh, I forgot to mention, the dod power jacks are similar to mono headphone jacks, 1/8" male...just to confirm.

[alphadog808]

Ok, I think I solved it...but I'm not sure WHY.  Anyways, I kept checking and looking over stuff and didn't see any issues....I got an email from the mod kit maker and he said it seemed like it was a grounding issue, so he suggested branching out a wire from the - connection to the chassis.  Tried it and the buzz went away!  But it did seem like I wasn't getting any gain, only volume...weird.  I then decided to put back diodes D1 and D2 and put the whole thing back together.  Now it works!  Even the LED for the 9v works...go figure. 

Anyone have any ideas why branching the - connection to the chassis would fix this problem?  Would this affect tone?  Is there anywhere else in the pedal where I could put this wire?

Thanks!!

[Paul Marossy]

Anyone have any ideas why branching the - connection to the chassis would fix this problem?  Would this affect tone?  Is there anywhere else in the pedal where I could put this wire?

If the DOD pedal was using the DC jack for it's connection to chassis ground, then when you put a plastic jack in it broke that connection - inviting the circuit to pick up all kinds of noise in the form of EMI (ElectroMagnetic Interference). Sounds like that was the case. Adding that ground wire will not affect the tone of the pedal at all. That ground wire you added could go anywhere as long as it's in contact with the chassis. But why fix it if it ain't broke?

[alphadog808]

Paul, you are absolutely right.  I looked at the DOD jack and the jacket is metal...and connects to the metal chassis...that's the ground I was missing, as you said.  Well, alls well that ends well, thanks all for the help!!

Jon

[Paul Marossy]

Paul, you are absolutely right.  I looked at the DOD jack and the jacket is metal...and connects to the metal chassis...that's the ground I was missing, as you said.  Well, alls well that ends well, thanks all for the help!!

Jon

Cool. Thanks for the verification on that, good to know.