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tony
Bronze Member
United Kingdom
142 Posts |
 Posted - 08/14/2008 : 17:34:33
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quote:
[i]
If you look at the schematic for the DD-2
you will see that the NE570 gets its 9V rail directly from before the
the LM78L05 regulator (IC10)
If I remember correctly you mentioned that the plug pack you WERE using has a really high voltage output,
over 20 Volts at one point if I recall, or was that a glitch with your multimeter?
The VCC on the NE570 is just a little over 20V.
Yeah, that was me using a mode on the multimeter which doubled the voltage reading, producing all manner of frightening results! The actual voltage was a normal input voltage.
Thanks for the data sheet links. Out of interest, during my searches I came across and equivalent chip - the SA571? It seemed virtually identical to the NE570 except for a really wide temperature rating, I think. I ordered the NE570 anyway as it's the proper part.
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/14/2008 : 18:15:34
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| 571 is the updated version - lower noise if i recall correctly. Not sure if it is *exactly* pin-for-pin, but it's close. |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/16/2008 : 18:04:35
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Right, update time.
Sad to say that in spite of of everything, your (Laurie and Dr Bob's) sage advice, my very professional soldering (!) and all the will in the world, the problem still persists. I still get all the same readings with very slightly different voltages probably due to the new NE570. It's a proper signetics one and it looks lovely sitting in there. Just wish it could sort the problem out!
I also replaced c21 out of desperation but to no avail. It just really sounds like both the feedback and effect level are being ground out somehow. |
Edited by - tony on 08/16/2008 18:08:11 |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/16/2008 : 19:29:33
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I've just thought of something - I've been measuring the control signal using the DC function of the meter when I guess I should have been using the AC function??
Edit:
AC on pin 16 shows nothing. Dc shows the usual .40 odd volts dropping to .05 or so. So no change there.
I did however notice something really interesting. Don't kill me, but when I was checking I accidentally checked pin 1, while I was doing this, the probe touched the ground lug which connects the pin 4 ground to (what I think is the) common ground. When I did this, I got massive loud overloading echoes that started to self oscillate. I didn't damage anything, because the pedal is the same as it was before.
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Edited by - tony on 08/16/2008 23:55:57 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/16/2008 : 21:05:07
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From what I can see in the circuit (without having a similar pedal to test) that looks OK.
What does it change to when the effect is turned off? Does it change on any position on the mode selector knob?
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/16/2008 : 21:06:18
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quote:
Originally posted by tony
Right, update time.
Sad to say that in spite of of everything, your (Laurie and Dr Bob's) sage advice, my very professional soldering (!) and all the will in the world, the problem still persists. I still get all the same readings with very slightly different voltages probably due to the new NE570. It's a proper signetics one and it looks lovely sitting in there. Just wish it could sort the problem out!
I also replaced c21 out of desperation but to no avail. It just really sounds like both the feedback and effect level are being ground out somehow.
Crap... Oh well, it was the next logical step. Take the measurements in the post above this one and let's move on. |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/16/2008 : 21:12:59
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Laurie, I just edited my above post with new information just as you posted yours! I'd been measuring off pin 1 by accident.
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Edited by - tony on 08/16/2008 21:14:06 |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/16/2008 : 21:48:22
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The measurements are the same whether the pedal is on or off and across all the modes. I get the usual voltage drop from .20v - .40 volts to .05v (approx) DC.
Measuring AC, I get a consistent .1v.
Really don't know if I should be measuring this (the control signal) AC or DC?
Hope you're having a pleasant Sunday BTW!!
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Edited by - tony on 08/16/2008 22:29:51 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/17/2008 : 00:35:51
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Saturday here still 
OK... measure the voltage at pin 5 of IC9 when the pedal is on and you change the mode switch (set to DC). What happens to it? Measure it again when you first apply power to the pedal.
EDIT: just looking at the data-sheet again and it's not immediately apparent, but it looks like Boss used pin 16 of the NE570 as a "mute" pin. If it turns out the measurements around pin 5 of IC9 show pin 5 to be at or near "0 volts DC" then I think we are on the trail of our culprit.
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Edited by - Laurie on 08/17/2008 00:50:26 |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/17/2008 : 01:17:30
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quote:
Originally posted by Laurie
Saturday here still
OK... measure the voltage at pin 5 of IC9 when the pedal is on and you change the mode switch (set to DC). What happens to it? Measure it again when you first apply power to the pedal.
EDIT: just looking at the data-sheet again and it's not immediately apparent, but it looks like Boss used pin 16 of the NE570 as a "mute" pin. If it turns out the measurements around pin 5 of IC9 show pin 5 to be at or near "0 volts DC" then I think we are on the trail of our culprit.
It IS getting weird...
That BA 634 is near impossible to find on the board, it's right down where it gets really messy.
Unfortunately, pin 5 shows around 9v DC consistently across all modes. The pedal turns itself off when pin 5 is touched with the probe, so it's necessary to turn it on while the probe is touching the pin. Just to confirm, the pin 5 I'm touching is the one that comes off R59...
On the subject of the NE570 pin 16 signal, that does seem sort of fine as with a guitar plugged in, if I pluck a string while reading the voltage it jumps up to about a volt , then fades as the note decays - whilst reading in DC.
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Edited by - tony on 08/17/2008 01:21:52 |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/17/2008 : 02:10:56
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FWIW, I consistently find zero volts on either side of R60 whether the effect is on or off.
Apologies for the relentless posts, I'm just keen to get this sorted.
Oh, and when the back cover is removed (but only when the back cover is removed) and I insert a power lead or an input jack while it's connected to the amp,I get the computer bleep, which is what I understand the muting circuit is there to suppress. I also get no real delays! the computer bleep is echoed in the same weak way as the guitar signal - this is why I was so excited about getting the delays from pin 1 of the NE570 - it proves that it's capable of producing them.
I think I'll call it a day for today (!) |
Edited by - tony on 08/17/2008 02:36:06 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/17/2008 : 02:45:47
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I'm tired too... OK, 9V on pin 5 is fine (it is the reset). Readings on R60 are fine too.
OK. To recap.
1) the reset circuit is OK (not stuck in "reset" mode - that was the test of pin 5 on the BA634)
2) the signal is strong going into pin 14 of the NE570 (good in) - so we have signal through the pedal electronics (this pretty much proves the digital delay circuitry is working)
3) there is crap coming out of pin 10 of the NE570 (bad out)
4) the NE570 is replaced with a known good one
5) the control/extrenal component connections to the NE570 seem OK
OK... the NE570 and surrounding circuitry semms OK. I'm starting to think it might be something pulling the output of the NE570 down. Can you desolder C29 and probe pin 10 of the NE570 to see if the signal is clear? That will tell us if Q8 or anything past it is futzed.
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/17/2008 : 13:45:44
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Good morning.....
With C29 taken out of the circuit I still get nothing from pin 10. Still get clear signal (ie - I can hear it clearly over the interference from my cable probe) from R44 and pins 14 and 15.
R42 and R41 are exactly to spec. I measure 2.86v DC across C20 with the effect on and that stays the same when I pluck strings.
Maybe I should just splash out on a more fully functioned meter...
Been meaning to get an oscilloscope as well for years now. |
Edited by - tony on 08/17/2008 13:51:45 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/17/2008 : 16:34:01
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quote:
Originally posted by tony
Good morning.....
With C29 taken out of the circuit I still get nothing from pin 10. Still get clear signal (ie - I can hear it clearly over the interference from my cable probe) from R44 and pins 14 and 15.
R42 and R41 are exactly to spec. I measure 2.86v DC across C20 with the effect on and that stays the same when I pluck strings.
Maybe I should just splash out on a more fully functioned meter...
Been meaning to get an oscilloscope as well for years now.
I picked up a good used Tektronix 2-trace CRO for $100 last year on ebay... Cheaper than a replacement delay pedal
Anyway, back to the fault. I am now stumped. Need to find some time to sit with the schematic and let it soak in. Will do that today. |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/17/2008 : 16:54:44
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Laurie, There's a lot of interference with the cable, also the room I'm doing this in is bad in general. I just got a bit of a "window" when the interference went very quiet and I tried all measurements again and found the following:
R44 - Clean signal, one clean repeat.
Both sides of C34 - the same.
Pin 10 - there is actually a signal - the single repeat, but it's very quiet - the same level as plugging in the pedal.
I guess what's happenig is that every time the repeat comes into the NE570 it's being crushed, so the delays disappear almost immediately- but it CAN'T be the chip now.
I feel we're really, really close. AAAArrggh!!!
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Edited by - tony on 08/17/2008 17:00:59 |
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Topic |
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DD 2 problems
