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Mesjoggah
Gold Member
Netherlands
595 Posts |
 Posted - 01/15/2009 : 21:54:11
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| LED replaced - works again. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/15/2009 : 23:04:58
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quote:
Originally posted by Mesjoggah
It is clear that my pedal lacks voltage on some point, so what component normally provides the necessery 5V where i measured 3V ?
Is this short of voltage most likely the problem or what is your opinion on this?
The current flows through C30 but when pulled it should also flow somewhere else (otherwise your pedal should be killed too)
I pulled C30 again tonight just to see if i was not mistaken by telling the pedal died, i saw the LED die but noticed the signal comes true like it always does.
The voltage comes from Q14 - the collector of Q14 gets set to 5V by the flip-flop when Q15 is "on" and Q14 is "off" - this is the normal state with the check LED on and the effect engaged.
One side of R45 is connected directly to the collector of Q14, and hence when the collector of Q14 is at 5V, that side of R45 is at 5V. Everything past R45 in the circuit is driven by this 5V.
R45 is connected to the gates of the two FET switches that turn on the effect. In between R45 and the FET gates are D1 and D5 - these diodes are to control the gate current. Also attached to the other side of R45 is C30 which is the "soft turn on" capacitor as noted previously.
Soooo... C30, D1, D5 and the gates of the switching FETs are all driven by the 5V applied to R45 by the collector of Q14.
Here is the interesting thing. For the voltage on R45 to be 5V on one side and 3V on the other, someting must be drawing current on the other side of R45 - 2 micro-Amps (2uA) to be exact (to get 2V drop across 1 Meg Ohms). There should be almost no (zero) current flowing through R45, so that the other side is also 5V like mine is.
Now, there is only C30, D1, D5 and the FET gates connected to the other side of R45, and:
- D1 and D5 and the FETs can not be pulling the 2uA and hence causing the voltage drop because we removed D1 and D5 (which removed the FETs as well) and the voltage still measured 3V.
- capacitors (C30 specifically) block DC current, so once C30 is charged (0.047 seconds) no current should flow and it can't pull the voltage down to 3V. We removed C30 and it's still 3V.
Need the photos, but in the mean time...
Can you please unsolder and lift just one end of R45 (point "D") and measure the voltage on the lifted end with the check LED on?
I've just had an epiphany... your meter might have an input impedance of around 1 Meg Ohms... and it it the meter itself that is pulling point "D" down to 3V! Measuring R45 with one end pulled will tell us yes or no on this for sure.
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Edited by - Laurie on 01/15/2009 23:08:52 |
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DeFrag
Moderator
USA
3409 Posts |
Posted - 01/16/2009 : 08:55:14
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OT: I think ol' Laurie should apply at:
Radial Engineering Ltd.
1638 Kebet Way
Port Coquitlam, BC Canada
V3C 5W9
Tel: 604-942-1001
Fax: 604-942-1010
Website: http://www.radialeng.com
Email: info@radialeng.com
I've always loved Radial Engineering's quality & usefulness; I have 3 or 4 of their units myself.
I was just reviewing their new products shown at NAMM & I must say I'm in  love with the company ever the stronger.
It seems right up Laurie's alley! |
Edited by - DeFrag on 01/16/2009 08:57:03 |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/16/2009 : 13:51:46
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quote:
Originally posted by Laurie
I've just had an epiphany... your meter might have an input impedance of around 1 Meg Ohms... and it it the meter itself that is pulling point "D" down to 3V! Measuring R45 with one end pulled will tell us yes or no on this for sure.
It's still only 3 volts
Here are some pictures:
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Edited by - Mesjoggah on 01/16/2009 14:20:50 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/16/2009 : 14:19:15
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quote:
Originally posted by Mesjoggah
It's still only 3 volts
Oh poop. We've been on a wild goose chase <sigh>
The 3V readings that I've been thinking are incorrect are actually caused by your multimeter. It also explains why the readings at point U/V are lower for you than me. My sincere apologies. I'm using an expensive "Fluke" brand meter that has a much higher input impedance than yours.
OK. Reset. Rewind. Knowing that some of the readings are skewed by the impedance of your meter, then all your readings (A thru W) are good.
Would you like to send your ODB-3 on a holiday to Canada? 
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/16/2009 : 14:21:33
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quote:
Originally posted by DeFrag
OT: I think ol' Laurie should apply at:
Radial Engineering Ltd.
1638 Kebet Way
Port Coquitlam, BC Canada
V3C 5W9
Tel: 604-942-1001
Fax: 604-942-1010
Website: http://www.radialeng.com
Email: info@radialeng.com
I've always loved Radial Engineering's quality & usefulness; I have 3 or 4 of their units myself.
I was just reviewing their new products shown at NAMM & I must say I'm in love with the company ever the stronger.
It seems right up Laurie's alley!
Thank you kindly DeFrag! I'm probably more likely to become a competitor to them than work for them though  |
Edited by - Laurie on 01/16/2009 14:37:15 |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/16/2009 : 14:35:36
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quote:
Originally posted by Laurie
quote:
Originally posted by Mesjoggah
It's still only 3 volts
Oh poop. We've been on a wild goose chase <sigh>
The 3V readings that I've been thinking are incorrect are actually caused by your multimeter. It also explains why the readings at point U/V are lower for you than me. My sincere apologies. I'm using an expensive "Fluke" brand meter that has a much higher input impedance than yours.
OK. Reset. Rewind. Knowing that some of the readings are skewed by the impedance of your meter, then all your readings (A thru W) are good.
Would you like to send your ODB-3 on a holiday to Canada?
Haha, i can still laugh about that and i was considering to send the pedal on a holiday to Canada as you mentioned.
I just hooked up the pedal and noticed that when i touch the middle leg of Q12 some distortion comes up, how's that? i can hear it's not what it should be but it might lead you in another direction?
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/16/2009 : 14:43:05
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quote:
Originally posted by Mesjoggah
Haha, i can still laugh about that and i was considering to send the pedal on a holiday to Canada as you mentioned.
I just hooked up the pedal and noticed that when i touch the middle leg of Q12 some distortion comes up, how's that? i can hear it's not what it should be but it might lead you in another direction?
It's important to not lose one's sense of humour with this stuff 
I'll look throug the summary of the symptoms again and see what I can think of to check next. If it was on my bench, the next thing I'd do is inject a test signal and trace it with the scope. We might need to consider building that test probe I mentioned in an earlier post - putting a 0.1�F capacitor on the end of a guitar lead so you can test to see where the signal goes.
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/16/2009 : 15:19:54
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I put together this:
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/16/2009 : 16:22:19
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quote:
Originally posted by Mesjoggah
I put together this:
Perfect! Can you please post this picture over on the "FAQ" forum as a reference for how it should be done...
I'll start probing my pedal tonight and let you know where "stick it" |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/17/2009 : 18:54:20
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OK... did some probing on my pedal.
Plug a lead into the input and apply a signal (I played a CD into my pedal). Clip the ground of the probe to the pedal case.
1) probe C2 (doesnt matter which side) - can you hear the input signal?
2) probe C3 (doesnt matter which side) - with the LED off, what can you hear? How about with the LED on?
3) probe C16 (doesnt matter which side) - with the LED off, what can you hear? How about with the LED on?
4) probe C10 (doesnt matter which side) - with the LED off, what can you hear? How about with the LED on?
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/18/2009 : 10:02:16
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quote:
Originally posted by Laurie
OK... did some probing on my pedal.
Plug a lead into the input and apply a signal (I played a CD into my pedal). Clip the ground of the probe to the pedal case.
1) probe C2 (doesnt matter which side) - can you hear the input signal? i can hear the input signal
2) probe C3 (doesnt matter which side) - with the LED off, what can you hear? How about with the LED on? i can hear the input signal not matter if the LED's on or off
3) probe C16 (doesnt matter which side) - with the LED off, what can you hear? How about with the LED on? i can hear the input signal not matter if the LED's on or off
4) probe C10 (doesnt matter which side) - with the LED off, what can you hear? How about with the LED on? there's no audio input signal not matter if the LED's on or off
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/18/2009 : 16:06:37
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Originally posted by Mesjoggah
1) probe C2 (doesnt matter which side) - can you hear the input signal? i can hear the input signal
Excellent!
2) probe C3 (doesnt matter which side) - with the LED off, what can you hear? How about with the LED on? i can hear the input signal not matter if the LED's on or off
This tells us Q2 is not switching. We do know though that the flip-flop driving Q2 is working
3) probe C16 (doesnt matter which side) - with the LED off, what can you hear? How about with the LED on? i can hear the input signal not matter if the LED's on or off
This tells us the opamp is working
4) probe C10 (doesnt matter which side) - with the LED off, what can you hear? How about with the LED on? there's no audio input signal not matter if the LED's on or off
this tells us the overdrive section of the pedal is not passing signal
I think you had an MT-2 you could use as a "donor" pedal? Can you swap Q2 in the ODB-3 for one of the 2SK118 FETs in the MT-2 and do the same probing again and let us know what happens? (2SK184 in the ODB-3 and the 2SK118 from the MT-2 are equivalent)
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 01/18/2009 : 17:26:51
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| I swapped Q2 with one from the MT-2 but the results are the same as before/ |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 01/18/2009 : 17:35:03
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This is driving me nuts.......
We know the flip-flop and drive to switch Q2 is working. We've just proved Q2 itself isn't faulty. There should be no signal on C3 when the LED is off.
Can you please post a picture of the tracks on the board around the opamp? THanks! |
Edited by - Laurie on 01/18/2009 17:40:53 |
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Topic |
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ODB-3 troubles
