BSIAB2 Lots of hum

[Buthut]

Ok, I put my pedal together and it has A-lot of hum in it. I can bias about half the hum out but then it goes directly to guitar fading away and crackeling. Turn it back the other way and fade away and crackel goes away and mega hum returns. The hum is so bad it won't even go away when i touch the strings. I tested all of the resistors. All of them tested the right ohms except one. The 1m resistor next to the ground wires makes my meter read 000. I tested my friends BSIAB pedal and his tests correctly. The other 1m resistor on the board tests correctly. I pulled the resistor off cause i thought it was bad and it tests correctly when it is not soldered on the board. Plus the new 1m resistor tests 000 when it was soldered on the board. So something is bad somewhere and i can't trace it down.

I did have a problem before this with my capacitor. I soldered it on backwords. Once i figured that out i killed it taking it off the board and got a new one to replace it. Is one of the other components messed up and playing havoc with the resistor. If my friends tests fine then mine should also. Or maybe the trim pot? Suggestions would be appreciated.

[LP Hovercraft]

If both 1 megs test 000, then yank the resistor and test the pads with no resistor soldered in.  If it still tests 000, the problem is that whatever the 1m is connected to on the non-ground side has shorted to ground somewhere.  Hum usually indicates a ground problem.  Hopefully this kills two birds w/ one stone.

[Buthut]

Well I took the resistor off the board  and tried to test the pads like you suggested and got no reading at all. Meter didn't go to 000 or anything. So i decided to pull the disc capacitor that was next to it off the board and test it. I could not get it to read in any way shape or form. Tried every method suggested on the net with a ohm meter. So i soldered the 1m resistor back on to the board and it tested normaly. So i'm thinking that capacitor is bad. I'll buy a replacement and post the results.

Thanks,

[iccaros]

what is the size of the cap, some meters can not measure a large range of cap's, mine once I get above 10uf and bellow .047 and its a high priced fluke.

can you post pictures of the board?

[Buthut]

The cap number is 251. That's all it has on there.



My multimeter ranges in ohms from 200 ohms, 2K, 20K, 200K, and 2M.  So i'm pretty sure it will read it but not 100%.

[Ice-9]

Is your meter capable of testing a capacitor, not all meters are. You can't test a cap using the Ohms scale,  well not correctly anyway.

[Buthut]

Well all i needed was to test if the cap was functioning at all. There are apparently several ways to do it but I can't get any reading on it. 

[Buthut]

Also noticed that the hum gets alot louder when i turn up the tone knob. It's an alpha B100K and wired correctly. Any ideas?

[LP Hovercraft]

Do a search on this site for an audio probe.  It consists of a 1/4" jack, a .1mF cap, and some hookup wire and is the most useful tool in my arsenal.  This may be an easier way of tracking that hum down than asking ?'s on the forum.

[Buthut]

Figured out the Hum issue. Apparentlly the jacks i have do not make contact with the pedal housing, which is very important for grounding. Those jacks have been nothing but a thorn in my side since i got them. But they look good. Had to solder a wire from the sleave lug to the tone knob. Replaced the cap and am now able to test the resistor next to it.  I finally have my pedal working. Stinking money pit.

[LP Hovercraft]

   I am glad you were able to find out the problem-non grounded jacks are rarely mentioned around here.  That's extremely frustrating, but on the up side, you can chalk it up to running into a very frustrating debug issue and coming out on top of it.  Sometimes persistence is what our pedals run on, more so than power.