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BF-2 Flanger Problem

Started by soupbone, September 14, 2011, 10:51:05 PM

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soupbone

September 14, 2011, 10:51:05 PM
I bought a used Boss BF-2 Flanger.When you kick the pedal "On" the effect doesn't come through about 75% of the time.Sometimes it comes on and works fine.Is it the switch that maybe going out?The led always comes on,so I'm guessing that's what it might be?Maybe?

Mark Hammer

#1
September 15, 2011, 08:46:19 AM
Like many commercial BBD-based effects, the BF-2 uses a single FET to connect/lift the wet signal to a mixer stage.  When the wet signal is connected, you get the effect.  When the wet signal is lifted such that only the constant dry signal remains, you don't get the effect.

If you go here - http://www.hobby-hour.com/electronics/s/boss-bf2-flanger.php - you can see the schematic and board layout.  Q4 is the component (JFET) of interest.  One of the pins of that JFET is connected to a diode.  The other two are the pins of interest.  If you bridge those two pins with a piece of wire, the pedal will always be "on" because there is no way to disable the wet signal.  If that restores the flanger's functioning, then clearly something is amiss with the switching.

Since the LED functions as per usual then the flip-flop portion of the switching system works.  Which suggests that it is something along the pathway incorporating R61, C38, D5, and Q4, and is most likely to be Q4.

Happily, these transistors are readily available from all the usual sources.

Govmnt_Lacky

#2
September 15, 2011, 09:30:19 AM
Minor hijack  :icon_rolleyes:

Could the calibration procedures for the BF-2 be used for other Flangers? Like the M117??

Particularly, the BBD bias and Regen/Resonance steps...  :icon_wink:
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Mark Hammer

#3
September 15, 2011, 09:31:48 AM
Looking over them, yeah, pretty much.

Govmnt_Lacky

#4
September 15, 2011, 10:09:47 AM
One last, quick question...

My computer does not have the "greatest" quality picture on it. Can someone confirm something for me?  :icon_redface:

On the BF-2 service notes, it looks like they ask you to place a screwdriver on TP2 while performing the Resonance adjustments.

Is TP2 the point where D3 and D4 connect to R11?

Sorry, my eyes deceive me sometimes! I just like to blame it on the equipment  :icon_lol:
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Mark Hammer

#5
September 15, 2011, 11:45:13 AM
It would seem to be.  If you look up BF-2 images, you'll find some gut shots, and a copper-side shot like this one ( http://www.pedalarea.com/images/boss_bf2_02.jpg ), and there is nothing else in that vicinity besides the junction of those two diodes.

Govmnt_Lacky

#6
September 15, 2011, 11:57:31 AM
Thanks Mark  ;D

Actually, I kind of asked the question the wrong way...  :icon_redface:

I am more or less wondering if the screwdriver is supposed to be used to directly short the diodes together at that point while adjusting for oscillation -OR- if the screwdriver is is just supposed to be touching one of the diodes  ???

The diodes are already shorted at this point via the trace so what would inserting the screwdriver do?
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Fender3D

#7
September 15, 2011, 12:31:29 PM
lol  :icon_mrgreen:
I was keeping my index finger away from mouse (another flanger thread... you know it's kinda paranoid....)
then I read it, and now you ask for something really odd...
where's the screwdriver statement?

Anyway TP1 is clock's test point,
TP2 looks a weird tp. you'd better check for autooscillation at IC2's pin 7, any point AFTER Q3 is good to check bias
"NOT FLAMMABLE" is not a challenge

Govmnt_Lacky

#8
September 15, 2011, 01:14:18 PM
Quote from: Fender3D on September 15, 2011, 12:31:29 PM
where's the screwdriver statement?

The "screwdriver statement" is from the Boss BF-2 Service Manual under the Resonance adjustment procedures.. Here is the link:

http://img22.imagevenue.com/img.php?image=31130_bf2_service_pg2_122_68lo.jpg

I am trying to "relate" this procedure to adjusting the trimmers in an M-117. I think I am almost there but I want to verify where to apply the amp & speaker when adjusting the Level (117)/Reson. (BF-2) trimmer to trim for oscillations..
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Mark Hammer

#9
September 15, 2011, 01:27:48 PM
The test point may be useful for finding the point where you can squeeze every last conceivable drop of resonance out of it before breaking into feedback, but you can probably identify the 98% perfect point by ear, without the need for test points, scopes, and such.  After all, Boss needs them all to sound the same, but you want yours to sound good to your ears, and you're perfectly capable of using yours to do just that.  Boss provides advice on how to make it idiot-proof, such that no owner anywhere on the planet will turn the resonance up full, wonder why it's howling, and return it as "defective".  In contrast, YOU know how it works and why it will do what it does.  So ignore the fine-tuning and just use the knobs, knowing that there may be some practical limitations to some settings.

Govmnt_Lacky

#10
September 15, 2011, 01:36:49 PM
@Mark

I agree that I can tune to my liking simply by using my ear and that anything out of the norm can be set through the pots on the front however,

Being the stickler that I am for precision adjustment, and the fact that I have had 3 people come to me already and ask to repair/look at their broken flangers (2 MXRs and 1 Boss) I would like to be able to return their units to spec. I figured I could apply the Boss adjustment procedures to the MXRs as they are similar in design.
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Fender3D

#11
September 15, 2011, 01:57:54 PM
LOL
alignement procedure requires you to use one out of your 10 upper biological signal generators to inject signal...  :icon_mrgreen:
"NOT FLAMMABLE" is not a challenge

Govmnt_Lacky

#12
September 15, 2011, 02:06:54 PM
Quote from: Fender3D on September 15, 2011, 01:57:54 PM
LOL
alignement procedure requires you to use one out of your 10 upper biological signal generators to inject signal...  :icon_mrgreen:

:icon_lol: 
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

soupbone

#13
September 17, 2011, 04:35:31 AM Last Edit: September 17, 2011, 04:37:41 AM by soupbone
Sorry for the late response everybody.I went to Dallas for my 40th birthday and partied it up. :icon_mrgreen: So,Do i need to maybe take out Q4 and put a new one in and see if that does the trick?Thanks for all the reponses!-soupbone

Fender3D

#14
September 17, 2011, 06:50:20 AM
Try bridging its left and right leads, as Mark suggested above, if it works then you're just 1 FET away to go
"NOT FLAMMABLE" is not a challenge

soupbone

#15
September 17, 2011, 07:59:00 AM
Quote from: Fender3D on September 17, 2011, 06:50:20 AM
Try bridging its left and right leads, as Mark suggested above, if it works then you're just 1 FET away to go
Cool!I'm a little unclear though on how to bridge the 2 pins? :-[

Fender3D

#16
September 17, 2011, 08:13:29 AM
just hook a short wire on them, a resistor lead will work fine
I this case, since you're looking for issues, you may short them with a tweezer like this http://www.banzaimusic.com/Tweezer-2327.html

PS
don't try this with a circuit with more than 30V on it, of course...
"NOT FLAMMABLE" is not a challenge

oldschoolanalog

#17
September 17, 2011, 12:55:37 PM
Is it just me or these flanger threads starting to look like "The Usual Suspects"... :icon_lol:
Mystery lounge. No tables, chairs or waiters here. In fact, we're all quite alone.

Govmnt_Lacky

#18
September 17, 2011, 02:07:01 PM
Quote from: oldschoolanalog on September 17, 2011, 12:55:37 PM
Is it just me or these flanger threads starting to look like "The Usual Suspects"... :icon_lol:

I believe in God...

But I fear Keyser Soze....... and debugging an M117  :icon_cool:
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Fender3D

#19
September 17, 2011, 02:22:59 PM
lol
the brotherhood of the flange...  :icon_mrgreen:

...and Gollum stole the last SAD   :'(
"NOT FLAMMABLE" is not a challenge
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