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Laurie
Double Platinum Member
Canada
4854 Posts |
 Posted - 01/03/2009 : 09:09:54
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Do you have a multimeter? Can you measure the voltage at the gate of Q2 (the middle leg)? Measure it when the LED is on, then when it is off. You might need to hold the probe on the gate leg and hit the pedal switch - the pedal might switch states when you touch the probe to the gate.
There is obviously some stuff missing from the schematic below (the bypass signal path) but let's try the measurement above and see what we get. |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/03/2009 : 12:31:32
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quote:
Originally posted by Laurie
Do you have a multimeter? Can you measure the voltage at the gate of Q2 (the middle leg)? Measure it when the LED is on, then when it is off. You might need to hold the probe on the gate leg and hit the pedal switch - the pedal might switch states when you touch the probe to the gate.
There is obviously some stuff missing from the schematic below (the bypass signal path) but let's try the measurement above and see what we get.
Yes, i do have a multimeter and measured Q2 (the middle leg), it reads zero volts no matter if it's turned off or on. The outer legs both read 0,52.
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Edited by - Mesjoggah on 01/03/2009 13:46:50 |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/03/2009 : 15:09:13
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I don't know i this will be much of a help..
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/03/2009 : 17:29:15
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quote:
Originally posted by Mesjoggah
quote:
Originally posted by Laurie
Do you have a multimeter? Can you measure the voltage at the gate of Q2 (the middle leg)? Measure it when the LED is on, then when it is off. You might need to hold the probe on the gate leg and hit the pedal switch - the pedal might switch states when you touch the probe to the gate.
There is obviously some stuff missing from the schematic below (the bypass signal path) but let's try the measurement above and see what we get.
Yes, i do have a multimeter and measured Q2 (the middle leg), it reads zero volts no matter if it's turned off or on. The outer legs both read 0,52.
Very interesting... and to confirm, the Check LED turns on and off?
Q2 (assuming the schematic is correct) is the "switch" FET that allows signal into the effected signal path. If it isn't switching (as indicated by your meter) then the signal path isn't switching from the non-effecred path to the effected path. This would explain why you don't hear any effected sound and the clipping LEDs don't light up.
What is VERY strange is that the Check LED cycles - that indicates the flip/flop is working.
Let me think on it some more and see if I can find a similar schematic.
EDIT: I reread you description of the fault, and I can't find anything explicit about the difference between "on" and "off". It's certainly implied, but to make sure I understand, I have one more question - what is the sound when you turn the pedal on and off? What is the sound like with the "check" LED on? Same question with the "Check" LED off? What (in detail) changes in the transition fro "on" to "off"?
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Edited by - Laurie on 01/03/2009 17:36:27 |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/03/2009 : 19:15:43
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quote:
Originally posted by Laurie
quote:
Originally posted by Mesjoggah
quote:
Originally posted by Laurie
Do you have a multimeter? Can you measure the voltage at the gate of Q2 (the middle leg)? Measure it when the LED is on, then when it is off. You might need to hold the probe on the gate leg and hit the pedal switch - the pedal might switch states when you touch the probe to the gate.
There is obviously some stuff missing from the schematic below (the bypass signal path) but let's try the measurement above and see what we get.
Yes, i do have a multimeter and measured Q2 (the middle leg), it reads zero volts no matter if it's turned off or on. The outer legs both read 0,52.
Very interesting... and to confirm, the Check LED turns on and off?
Q2 (assuming the schematic is correct) is the "switch" FET that allows signal into the effected signal path. If it isn't switching (as indicated by your meter) then the signal path isn't switching from the non-effecred path to the effected path. This would explain why you don't hear any effected sound and the clipping LEDs don't light up.
What is VERY strange is that the Check LED cycles - that indicates the flip/flop is working.
Let me think on it some more and see if I can find a similar schematic.
EDIT: I reread you description of the fault, and I can't find anything explicit about the difference between "on" and "off". It's certainly implied, but to make sure I understand, I have one more question - what is the sound when you turn the pedal on and off? What is the sound like with the "check" LED on? Same question with the "Check" LED off? What (in detail) changes in the transition fro "on" to "off"?
There's absolutely no difference in sound with the check LED on or off Laurie |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/03/2009 : 22:15:56
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OK... it seems clear that the leg of the flip-flop that isn't driving the LED has failed somehow. The flip-flop itself is working - we know this because the LED turns on and off. If the flip-flop itself had failed, the LED would be always on or always off.
The fault must be somewhere between the output of the flipflop and the FET bypass switches. There isn't much in that part of the circuit.... almost has to be a failed track?
I'll take mine apart later today or tomorrow and trace the circuit and give you some more measurements to do.
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Edited by - Laurie on 01/03/2009 22:17:43 |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/03/2009 : 23:08:30
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quote:
Originally posted by Laurie
OK... it seems clear that the leg of the flip-flop that isn't driving the LED has failed somehow. The flip-flop itself is working - we know this because the LED turns on and off. If the flip-flop itself had failed, the LED would be always on or always off.
The fault must be somewhere between the output of the flipflop and the FET bypass switches. There isn't much in that part of the circuit.... almost has to be a failed track?
I'll take mine apart later today or tomorrow and trace the circuit and give you some more measurements to do.
That's ok Laurie, your help is much appreciated!!
in fact i'm feeling a bit stupid now because it is obvious i don't know that much of electric circuits, my only experience is with modding which is a lot more simpler!
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Edited by - Mesjoggah on 01/03/2009 23:09:30 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/04/2009 : 00:38:42
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Hey... don't worry. This stuff is pretty much Greek until you get your head around it (and that usually takes a bunch of courses).
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/04/2009 : 16:16:50
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| Laurie, the level knob affects the sound a bit as i stated before, but today i found out that it also affects the sound when the pedal is turned off! |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/04/2009 : 17:40:15
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| OK... I'll crack mine open today and have a look. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/06/2009 : 17:01:00
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quote:
Originally posted by Laurie
OK... I'll crack mine open today and have a look.
I forgot to do that, didn't I? Will dig the ODB-3 out tonight. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/07/2009 : 10:19:11
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Righto! Some tests.
1) Make sure the "check LED" is OFF. Measure from the "stripe end" of D1 to the pedal case. Measure from the "stripe end" of D4 to the pedal case.
2) Make sure the "check LED" is ON. Measure from the "stripe end" of D1 to the pedal case. Measure from the "stripe end" of D4 to the pedal case.
What this has tested is the drive to the bypass/effect FET switches (I tried measuring the gate of Q2 and the control voltage is so low it didnt register on my meter - just like it didnt register on yours).
Anyway, the tests above will tell us definitively if the FET switch drive is working. Let us know the result!
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Edited by - Laurie on 01/07/2009 10:21:30 |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/07/2009 : 17:21:41
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quote:
Originally posted by Laurie
Righto! Some tests.
1) Make sure the "check LED" is OFF. Measure from the "stripe end" of D1 to the pedal case. Measure from the "stripe end" of D4 to the pedal case.
2) Make sure the "check LED" is ON. Measure from the "stripe end" of D1 to the pedal case. Measure from the "stripe end" of D4 to the pedal case.
What this has tested is the drive to the bypass/effect FET switches (I tried measuring the gate of Q2 and the control voltage is so low it didnt register on my meter - just like it didnt register on yours).
Anyway, the tests above will tell us definitively if the FET switch drive is working. Let us know the result!
Laurie, i measured both d1 and d4 with the 'check LED' off, both zero volts, then i measured both d1 and d4 with the 'check LED' on, both read 3 volts (i measured from the stripe end) |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/07/2009 : 17:24:46
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OK... the flip-flop has failed somehow. They should read 0V and 5V, then 5V and 0V (the voltage should flip when the pedal is pushed).
How bright is the "check LED" when it is on? As bright as other MIT pedals?
I'll poke inside mine a bit more and give you another set of measurements to narrow the fault down.
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/07/2009 : 18:10:47
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| I would say the LED is a little less brighter compared to other MIT pedals. |
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Topic |
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ODB-3 troubles
