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Mesjoggah
Gold Member
Netherlands
595 Posts |
 Posted - 06/06/2009 : 17:45:26
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So, today the mail brought me another dead DD-3, this one is really dead- nothing happens when plugged in. The former owner had it lying in a closet for years with a leaking battery in it.. he doesn't know anything of the pedal as he got it as a gift years ago when he bought another pedal.
This is how it looks right now:
D6 has been removed and there's an alternative tracing, there's an ic put on a bracket and the ac power in has been re-wired.. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/06/2009 : 18:36:35
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quote:
Originally posted by Mesjoggah
there's an ic put on a bracket and the ac power in has been re-wired..
Need some clearer photos of these. is the IC you refer to the diode on the back of the power connector? Or something not shown in the pics?
Some close-ups of the component side of the board and solder side too please - maybe 1/4 of the board in each photo so the barrel distortion isn't so bad?
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 06/06/2009 : 19:52:59
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| SG7400 is on a socket, i resoldered the ac power in and now the LED goes on and clean signal passes through, no delay yet. |
Edited by - Mesjoggah on 06/06/2009 20:35:46 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/07/2009 : 00:15:47
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quote:
Originally posted by Mesjoggah
SG7400 is on a socket, i resoldered the ac power in and now the LED goes on and clean signal passes through, no delay yet.
Ah gotcha about the 7400.
Check Q9 - it is on the edge of the board and we've seen a couple of these with broken legs because they are folded over to fit above the jack. Sometimes the breaks are invisible. Test the junctions of Q9 with a diode tester if you have one.
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 06/07/2009 : 14:39:46
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quote:
Originally posted by Laurie
quote:
Originally posted by Mesjoggah
SG7400 is on a socket, i resoldered the ac power in and now the LED goes on and clean signal passes through, no delay yet.
Ah gotcha about the 7400.
Check Q9 - it is on the edge of the board and we've seen a couple of these with broken legs because they are folded over to fit above the jack. Sometimes the breaks are invisible. Test the junctions of Q9 with a diode tester if you have one.
My diode tester says diode is ok, audio probe says no signal there. I suspect NE570 to be the fault because i have no signal out.
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Edited by - Mesjoggah on 06/07/2009 15:42:44 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/07/2009 : 16:32:54
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Q9 is on the input to the NE570 (expander part), so no signal on Q9 means no signal on output of NE570 expander (I've never seen an NE570 fail...).
Probe these places. What do you get?
1) IC4 pin1
2) R23 - the side that goes to Q6
Do you have 5VDC on pin 64 of the long-chip?
Hmmmm.... do you have any way of detecting if the clock for the long-chip is running? I'd normally use a scope to see if there was a several MHz clock signal on pin 9 of the 7400.
The reason I ask is that if I recall the theory correctly, a 7400 chip (like in your pedal) won't self oscillate the same way a 74HC00 will (the "HC" chip is the one that should be there). I think it needs to be a CMOS chip (the "C" in "HC"), but I could be wrong. If you find a clock signal, then all is well.
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Edited by - Laurie on 06/07/2009 16:43:27 |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 06/07/2009 : 17:11:12
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| Laurie, on my working DD-3 i have signal on pin 2,3,7,12 & 13 of the NE570N and on this faulty one i only have signal on pin 2,3 and 7. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/07/2009 : 17:17:04
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quote:
Originally posted by Mesjoggah
Laurie, on my working DD-3 i have signal on pin 2,3,7,12 & 13 of the NE570N and on this faulty one i only have signal on pin 2,3 and 7.
I'm guessing you mean pin 14? (pin 13 is the 9V supply) Anyway, that is consistent with no signal on Q9. Q9 comes in front of the NE570, so no signal on Q9 guarantees no signal on pins 12 and 14. Signal on pin 7 means the NE570 is alive (there would be nothing on pin 7 if it was completely dead)
The problem has to be somewhere in front of Q9. |
Edited by - Laurie on 06/07/2009 17:18:16 |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 06/08/2009 : 16:21:02
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quote:
Originally posted by Laurie
Q9 is on the input to the NE570 (expander part), so no signal on Q9 means no signal on output of NE570 expander (I've never seen an NE570 fail...).
Probe these places. What do you get?
1) IC4 pin1 signal
2) R23 - the side that goes to Q6 signal
Do you have 5VDC on pin 64 of the long-chip? Yes, i have
Hmmmm.... do you have any way of detecting if the clock for the long-chip is running? I'd normally use a scope to see if there was a several MHz clock signal on pin 9 of the 7400. I do not have a scope, is there another way to do this?
The reason I ask is that if I recall the theory correctly, a 7400 chip (like in your pedal) won't self oscillate the same way a 74HC00 will (the "HC" chip is the one that should be there). I think it needs to be a CMOS chip (the "C" in "HC"), but I could be wrong. If you find a clock signal, then all is well.
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Edited by - Mesjoggah on 06/08/2009 17:11:10 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/09/2009 : 01:22:55
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Signal on IC4 pin 4 tells us that the signal is getting through most of the analogue input circuitry.
Next tests will need the volume on the probe amp turned way down. If everything is working, you will get digital noise at some of the test points. (should hear the test signal buried in digital hash/mud)
1) IC3 pin 7
2) IC5 pin 7
3) IC6 pin 3
4) IC3 pin 3
5) IC3 pin 1
What we are doing is tracing the signal through the sample-and-hold circuit (the DD-3's answer to A/D and D/A convertors).
Not sure how to test for clock signal without a scope. It is WAY outside audio range (1MHz+). Well, if you don't hear the signal through the sample-and-hold we'll know the smaple-and-hold isn't being driven by the long-chip. If you have easy access to a parts shop, just replace the 7400 with a 74HC00 anyway.
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 06/09/2009 : 07:12:28
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quote:
Originally posted by Laurie
Signal on IC4 pin 4 tells us that the signal is getting through most of the analogue input circuitry.
Next tests will need the volume on the probe amp turned way down. If everything is working, you will get digital noise at some of the test points. (should hear the test signal buried in digital hash/mud)
1) IC3 pin 7
2) IC5 pin 7
3) IC6 pin 3
4) IC3 pin 3
5) IC3 pin 1
What we are doing is tracing the signal through the sample-and-hold circuit (the DD-3's answer to A/D and D/A convertors).
Not sure how to test for clock signal without a scope. It is WAY outside audio range (1MHz+). Well, if you don't hear the signal through the sample-and-hold we'll know the smaple-and-hold isn't being driven by the long-chip. If you have easy access to a parts shop, just replace the 7400 with a 74HC00 anyway.
In my working DD-3 i get a good signal on all those pins, on the dead one i get none except from typical electric buzz on some of the pins on ic3 ( i do have a problem determing what's pin1 on this ic?) |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/09/2009 : 14:42:30
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OK. Your amp probably has enough high frequency filtering to remove the sampling artifacts.
Try IC3 pin5. I'm guessing that you won't find signal there. Assuming that is the case, what this tells us is that either the long-chip isn't working (there is no "SAH" signal coming from the long-chip), or that IC4 has failed (the SAH signal is there, but IC4 isn't doing anything). Again, if we had a scope we could check pin 5 of IC4.......
I might be blind to something else here, but my money is on the clock not running because it needs a 74HC00 rather than a 7400. This would mean the long-chip isn't being clocked, so isn't doing anything. I wish there was some way we could check it. Does someone you know have a scope? (would you be willing to buy one?  ) A quick probe on pin 63 of the long-chip with a scope would tell is if it was running.
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/09/2009 : 16:30:05
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| I'm looking at the soldering of the socket for the 74HC00 socket. Can you check that very carefully - the angle isn't perfect, but it looks a little "blobby" - maybe it didn't take properly? |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 06/09/2009 : 20:03:17
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I went to a close neighbour who has a scope, he said there's no signal on ic4 pin5 and a faint one on pin63 of the long chip.
Since i don't know how a scope works i for myself can't say anything about it.
i try to order a new 74HC00 and see what happens when it's in place. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/09/2009 : 20:11:08
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No signal on IC4 pin 5 means the SAH isn't being clocked. "faint" signal on pin63 of the long-chip doesn't sound good and would be in line with the long-chip not clocking IC4.
Did he say what "a faint one" means? It should be about 1.5MHz square wave at 5V peak-to-peak. This would normally be described as 'strong' when viewed on a on a scope.
If you check the socket and change the chip, then check the signal again...? Heck, I've been wrong many times before, but my money is on this clock signal.
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Edited by - Laurie on 06/09/2009 21:57:19 |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 06/11/2009 : 16:50:15
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I found and ordered a 74hc00 which came in the mail today and thanks to one of the previous attempted repairs in which someone placed a socket for this IC it was an easy switch, And Laurie, you were right!!
After i placed the IC it came alive and works just fine!
Another resurrected DD-3!
Thanks Laurie for helping me out again! 
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Edited by - Mesjoggah on 06/11/2009 17:00:28 |
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another dead DD-3 thread..
