Boss pedal won't turn off

[badoogie]

I have a Boss EH-2 which is permanently switched on. I suspected the problem was with the switch, but I checked it with the continuity tester on my multimeter and it seems fine (contact is made when the switch is engaged, broken when the switch is released). I also tried jumping the two contacts on the switch, but this had no effect.

Any ideas what the problem can be? Can I test the components in the switching circuit?

[PRR]

Welcome.

Does the LED go on/off?

http://www.freeinfosociety.com/media/images/4077.png

[badoogie]

Thanks PRR. 

The LED stays on all the time.

[PRR]

Then the flip-flop lower right is not flip-flopping.

Others here know much more about this than I do.

I'll guess they want to know the FF's collector and base voltages, and how they change when switch is hit.

There is also an excellent background paper at Geofex:
http://www.geofex.com/Article_Folders/bosstech.pdf

[badoogie]

Okay, I took some readings  :

Q1

E = 0.87V
C = 73.7mV
B = 0V

Q2

E = 49.8mV
C = 23.2mV
B = 1.7mV

[Mark Hammer]

Some service manuals for Boss pedals make mention of problematic or unreliable switching and propose a fix involving either increasing OR decreasing the pf value of the caps.  I forget which direction.  I'll need to dig up the relevant notes.

[reddesert]

Referring to the schematic posted earlier, http://www.freeinfosociety.com/media/images/4077.png, the emitters of both Q1 and Q2 should be grounded.  Your voltages have everything near zero except one of the emitters at 0.9 V. If that's right, the flip flop won't work. I'd suggest checking the pinouts again, and looking for a loose ground connection.

[Quackzed]

propose a fix involving either increasing OR decreasing the pf value of the caps.  I forget which direction.

-- increasing-- bigger caps will slow down the flip and flop and prevent it from flip/flop/flipping or flop/flip/flopping? such that when you press it it might switch states twice or more (instead of on to off itll on to off to on again and still be on... ive used .01uf caps and it worked fine... couldn't stomp fast enough to notice any slowing... but the actual switches are the usual culprit, then the pf caps, but in this case it looks like the emitters of the switching trannys arent well grounded from the v readings as mentioned...

[badoogie]

Thanks for the replies guys.     I checked the datasheet again and embarrassingly I did get the pinouts wrong.     Those readings should have been as follows:

Q1

B = 0.87V
C = 73.7mV
E = 0V

Q2

B = 49.8mV
C = 23.2mV
E = 1.7mV

I checked the emitters and they both seem to have a good connection to ground.

[reddesert]

OK, good progress. So read the geofex article linked above http://www.geofex.com/Article_Folders/bosstech.pdf carefully. Q1 and Q2 are set up as a pair. If Q1 is conducting (base above emitter by more than a diode drop), then Q1's collector should be low (yes from your voltages), and it should turn Q2 off (yes), and the collector of Q2 should be high, close to +9V (no).  This isn't happening, so you now need to figure out why - loose connection somewhere, eg between the collector of Q2 and its path to +9V? short? bad component?

[PRR]

Not making sense.



Q1 is "on", as it should be with 870mV on Base. Its Collector pulls to 74mV, a likely value. 100K:56K makes 23mV at Q2 Base, OK. But Q2 should be "off". Why is its collector "low" (transistor on)? And the real stinker: how can Q1 B be at 870mV when nothing going into it is even 100mV?

Bad joint? Bad reading? ??

[TejfolvonDanone]

Bad joint? Bad reading? ??

I'd like to add: Collector to emitter short type of fault?

[Erry]

I know this is an old topic but I just want to share my same problem. My Boss DS2 had same problem, it wont' turn off. I know so little about electronic part so I don't know where to start about the component. I decided to check switch instead. I took out the switch, but desolder the short one cable first to make it easy to take it out. And then I disassamble the switch to look what inside. I found there are two metal plate inside and looked dirty, lot of oxidized thing. So i clean them using contact cleaner, especially the surface they shoud contact each other. Then put the switch back together, solder the cable and yes it works, It can be turn off. It failed for some attempts but i kept pushed the knob on and off and then everything work ok. Problem solved.
Btw be carefull when disassamble the switch, it is made from plastic, you can easly broke the clips that hold them together if you don't careful.

[GibsonGM]

Good DIY, Erry, not diminishing your work in the slightest - but for all the work involved, a person could get a new switch and just install it, with the benefit of it being new so has many many cycles in its lifetime left...     

[duck_arse]

and, welcome to the forum!