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Laurie
Double Platinum Member
Canada
4854 Posts |
 Posted - 01/07/2009 : 18:18:02
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quote:
Originally posted by Mesjoggah
I would say the LED is a little less brighter compared to other MIT pedals.
OK - that makes sense. I'll have the next set of measurements later today. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/08/2009 : 07:10:29
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Transistors Q1 and Q15 are the flip-flop transistors.
A couple of dumb questions first:
1) are Q1 and Q15 properly oriented? Does the "curve" of the back of the transistor align with the "curve" of the transistor diagram drawn on the board?
2) is the pedal switch giving a good positive contact? Ensure the pedal is unplugged. Set your meter to "Ohms" and measure from the pedal case to "P7" where the purple wire joins the board. The meter should read a clean "zero" Ohms when the switch is depressed, and infinite Ohms (clean open circuit) when the switch is not pressed.
If all the stuff above is OK, turn the pedal on and take the following measurements:
a) Ensure the "check LED" is ON. Measure the voltage from the leg of Q15 closest to R47 across to the pedal case. It should be close to 0.6 Volts. Measure the voltage from the leg of Q1 furthest from the edge of the board across to the pedal case. It should be 0 Volts.
b) Ensure the "check LED" is OFF. Measure the voltage from the leg of Q15 closest to R47 across to the pedal case. It should be 0 Volts. Measure the voltage from the leg of Q1 furthest from the edge of the board across to the pedal case. It should be close to close to 0.6 Volts.
These are the readings from my known good pedal - what does your pedal read?
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Edited by - Laurie on 01/08/2009 07:20:40 |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/08/2009 : 18:07:51
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quote:
Originally posted by Laurie
Transistors Q1 and Q15 are the flip-flop transistors.
A couple of dumb questions first:
1) are Q1 and Q15 properly oriented? Does the "curve" of the back of the transistor align with the "curve" of the transistor diagram drawn on the board?
They are properly oriented
2) is the pedal switch giving a good positive contact? Ensure the pedal is unplugged. Set your meter to "Ohms" and measure from the pedal case to "P7" where the purple wire joins the board. The meter should read a clean "zero" Ohms when the switch is depressed, and infinite Ohms (clean open circuit) when the switch is not pressed.
no troubles here
If all the stuff above is OK, turn the pedal on and take the following measurements:
a) Ensure the "check LED" is ON. Measure the voltage from the leg of Q15 closest to R47 across to the pedal case. It should be close to 0.6 Volts. Measure the voltage from the leg of Q1 furthest from the edge of the board across to the pedal case. It should be 0 Volts.
Q15 LED on = 0,6 volts
Q1 LED on = 1,1 volts
b) Ensure the "check LED" is OFF. Measure the voltage from the leg of Q15 closest to R47 across to the pedal case. It should be 0 Volts. Measure the voltage from the leg of Q1 furthest from the edge of the board across to the pedal case. It should be close to close to 0.6 Volts.
Q15 LED off = 0 volts
Q1 LED off = 1,1 volts
These are the readings from my known good pedal - what does your pedal read?
Hopefully you can do something with my measurements, it's still a bit greek to me..
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/08/2009 : 22:46:08
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Q1 and Q15, are they swapable? Q1 is a k184 amd q15 is a c2458?
I will check things tomorrow. it is late night here and i really need some sleep as i am doing some overtime at work.. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/08/2009 : 22:52:01
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quote:
Originally posted by Mesjoggah
Q1 and Q15, are they swapable? Q1 is a k184 amd q15 is a c2458?
I will check things tomorrow. it is late night here and i really need some sleep as i am doing some overtime at work..
Good catch! I blame the head-cold I've got... That entire measurement post above should have read Q14 and Q15 (not Q1). I mistyped the first time the cut-and-pasted the error!
Can you measure again - Q14 instead of Q1?
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/09/2009 : 05:43:06
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quote:
Originally posted by Laurie
quote:
Originally posted by Mesjoggah
Q1 and Q15, are they swapable? Q1 is a k184 amd q15 is a c2458?
I will check things tomorrow. it is late night here and i really need some sleep as i am doing some overtime at work..
Good catch! I blame the head-cold I've got... That entire measurement post above should have read Q14 and Q15 (not Q1). I mistyped the first time the cut-and-pasted the error!
Can you measure again - Q14 instead of Q1?
ah, good i didn't solder it out yet!!!
q14 measures 0 when LED is on and 0.6 when LED is off, same as yours. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/09/2009 : 06:03:28
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Excellent! So the flip-flop itself is working, but Q14 is not driving Q2.
So let's trace the signal.
The middle leg of Q14 should be changing from 0V to about 5 or 6 volts with the check LED going on and off as you pless the switch.
Both sides of R45 should be changing from 0V to about 5 or 6 volts with the check LED going on and off as you pless the switch.
The wire link closest to R45 should be changing from 0V to about 5 or 6 volts with the check LED going on and off as you pless the switch.
What does your pedal do?
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/09/2009 : 10:20:17
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quote:
Originally posted by Laurie
Excellent! So the flip-flop itself is working, but Q14 is not driving Q2.
So let's trace the signal.
The middle leg of Q14 should be changing from 0V to about 5 or 6 volts with the check LED going on and off as you pless the switch.
0 volts no matter if the LED is on or not
Both sides of R45 should be changing from 0V to about 5 or 6 volts with the check LED going on and off as you pless the switch.
the outer side doesn't change and the inner side changes to 3 volts
The wire link closest to R45 should be changing from 0V to about 5 or 6 volts with the check LED going on and off as you pless the switch.
I am not exactly sure which wire link you mean?
What does your pedal do?
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/09/2009 : 14:27:47
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Q14 is receiving drive to the base (the 0.6V measured). But Q14 is not "switching" - the middle leg is 0V all the time.
For Q14 to not be switching, one of three things must be happening:
1) Q14 is broken
2) there is a short circuit to ground from the collector of Q14
3) the collector resistor of Q14 is open circuit
Set your meter to ohms and measure from the middle leg of Q14 to the pedal case - what resistance do you get? (it should be infinite - an "open circuit")
Set your meter to Ohms and measure R46 - it's a 56k resistor but while it is still in circuit, mine measures about 40k. What does yours measure? |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/09/2009 : 16:03:59
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quote:
Originally posted by Laurie
Q14 is receiving drive to the base (the 0.6V measured). But Q14 is not "switching" - the middle leg is 0V all the time.
For Q14 to not be switching, one of three things must be happening:
1) Q14 is broken
2) there is a short circuit to ground from the collector of Q14
3) the collector resistor of Q14 is open circuit
Set your meter to ohms and measure from the middle leg of Q14 to the pedal case - what resistance do you get? (it should be infinite - an "open circuit")
0,6(on a 20k scale)
Set your meter to Ohms and measure R46 - it's a 56k resistor but while it is still in circuit, mine measures about 40k. What does yours measure?
56k
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/09/2009 : 16:21:04
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OK. It is either Q14 itself, or somewhere there is a short from the collector circuit of Q14 to ground.
Pull Q14 out of the board and measure the resistance between the two legs that were closest to the edge of the board. Should be infinite Ohms (open circuit).
With Q14 out of the board, measure from the solder pad for the middle leg of Q14 to ground (the pedal case). Should be infinite Ohms (open circuit).
What do you get?
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/09/2009 : 16:51:22
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quote:
Originally posted by Laurie
OK. It is either Q14 itself, or somewhere there is a short from the collector circuit of Q14 to ground.
Pull Q14 out of the board and measure the resistance between the two legs that were closest to the edge of the board. Should be infinite Ohms (open circuit).
there's no reading
With Q14 out of the board, measure from the solder pad for the middle leg of Q14 to ground (the pedal case). Should be infinite Ohms (open circuit).
there's no reading
What do you get?
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/09/2009 : 17:15:55
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That's a bit bizarre... Getting a reading with it in circuit and no reading with it out of circuit.
If it was me, i'd swap Q14 and Q15 at this point and see if it changed to "effect always on". |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/09/2009 : 18:22:53
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quote:
Originally posted by Laurie
That's a bit bizarre... Getting a reading with it in circuit and no reading with it out of circuit.
If it was me, i'd swap Q14 and Q15 at this point and see if it changed to "effect always on".
it might be a misunderstanding, if the circuit is closed the meter should read zero resistance, right?
And with an open circuit the meter should read 1, no measurements, infinite?
If that is the case it is infinite.
I swapped Q14 with the same type transistor from a MT-2, the MT-2 works with this Q14 transistor and the ODB remains the same with the known good MT-2 transistor. |
Edited by - Mesjoggah on 01/09/2009 18:23:52 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/09/2009 : 18:45:53
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These are the things that don't fit together in my mind:
1) Set your meter to ohms and measure from the middle leg of Q14 to the pedal case - what resistance do you get? (it should be infinite - an "open circuit") 0,6(on a 20k scale)
This tells us that there is a connection from the collector of Q14 to ground. There should not be one - mine reads infinite.
2a) Pull Q14 out of the board and measure the resistance between the two legs that were closest to the edge of the board. Should be infinite Ohms (open circuit). there's no reading
2b) With Q14 out of the board, measure from the solder pad for the middle leg of Q14 to ground (the pedal case). Should be infinite Ohms (open circuit). there's no reading
In point #1 above, there is a reading to ground. With Q14 pulled, that reading should occur either inside Q14 (it does not - point #2a) or in the circuit on the board (it does not - point #2b).
OK. Let's check this - with the pedal powered up, is there 9V between the pedal case and the side of R46 furthest from the edge of the board?
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ODB-3 troubles
