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Laurie
Double Platinum Member
Canada
4854 Posts |
 Posted - 06/01/2009 : 03:25:17
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EDIT: see pics of completed repair later in the thread
G'day! So I've had dead a long-chip DD-3 in the parts bin for a few months and I finally decided to try to bring it back to life. This is the "cats pee" pedal I mentioned in another thread.
Needed a new mode switch. Once the switch was fixed there were almost no echos - they were very, very faint. Found C34 was open circuit. Fixed that.
Now... everything works as it should except that all the normal feedback control happens in the first 25% of the travel of the feedback pot. 0% on the feedback pot gives no feedback, and 25% on the feedback pot gives infinite echoes as you would expect with the feedback pot maxed.
Anything over 25% on the feedback pot causes massive distorted infinite oscillations. The distortion is square-wave clipping of the signal due to infinite boosting (each repeat is boosted compared to the last). With the feedback pot set to maybe 30% the onset of the distortion is slow, with the feedback pot set to 100% the onset is immediate.
It is clear that the feedback signal being sent back into the compressor through C26 is too hot.
Fault finding so far:
- checked the gain of all the buffers and they are all close to unity (I wondered if one of them had a faulty feedback resistor and had gone high gain)
- replaced the NE570 (no change)
- confirmed signals into and out of NE570 (all seem good), and that the NE570 was compressing and expanding as it should (EDIT: no it wasn't)
- confirmed all off-board wiring (no issues)
- confirmed feedback pot is properly grounded and that it divides the voltage properly
Spent about 2 hours probing the circuit trying to find where there might be a fault. Nothing so far.
The only thing I can think might be causing this is if the NE570 is expanding more than it is compressing (ie. giving a net amplitude gain with a pass through the compression/expansion cycle). It's not the NE570, so it must be the outbaord components - anyone know exactlyy hoiw this chip works? What outboard component failure could be causing it to fail to compress?
Any hints/thoughts would be most appreciated.
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Edited by - Laurie on 06/03/2009 13:33:59 |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 06/01/2009 : 16:31:42
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Hi Laurie
Are you able to use your DD-2 to do an A-B comparison with the faulty DD-3 Long chip (cat pee enhanced Ver./option)?
It will probably give you more meaningful insight between the working DD-2 & DD-3.
What do you think made C34 go open? (cat pee?)
In Ref to the Sch. are you getting the same or similar waveforms on your CRO?
Check for a "resistive track" from the corrosion caused by the cat pee.
Now --- if you only had on of them there "New Fangled ESR meters"?
Regards Dr. Bob 
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/01/2009 : 18:34:47
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Thanks Dr. Bob!
Tracks are all OK. C34 went open... just because  The leads were a bit discouloured though. I wondered if a fault in the NE570 might have been the cause, but a replacement NE570 behaves identically.
I tried the DD-2 side by side but didn't really get anywhere with it. Maybe I just need to do it again and be more methodical.
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/03/2009 : 01:11:35
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Had to be the compressor... C31 was open, so the RECT-IN and G_CELL_IN pins of the NE570 weren't being driven. This meant that the compressor wasn't compressing. What gave it away was the increasing repeats had exponentially increasing noise... so the noise suppression of the compress/expand cycle wasn't happening.
Checked the rest of the electros in the area and it was only the 10�F value that was affected. The 1�F caps nearby were pristine.
Anyway, all is well. I've cleaned out the corrosion in the battery compartment, given the area a coat of paint, replaced the battery snap... and I have another long-chip delay rescue pedal 
Pics to follow after the paint and conformal coating are dry.
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Edited by - Laurie on 06/03/2009 06:07:18 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/03/2009 : 12:32:33
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In case anyone is interested, here is the repair "in pictures". Entire exercise (including fabricating the switch circuit board) took about 10 hours. A pretty expensive pedal by now I guess, but the rescue had to be done
This is what the board looked like at the start. Also there was no mode switch and the pedal was generally not working.
Cats pee corrosion cleaned off.
All joins resoldered.
Board protected with conformal coating.
Mode switch replaced. Fabricated the small circuit board for the switch.
Once the corrosion was removed and the mode switch replaced, the pedal had no echoes. Replaced C34 to fix that problem. Once echos were restored, the echo level was HUGE and distorted. Replaced C31 to restore the compressor part of the NE570 compandor. Replaced Q9 because it had been bent so severely that the legs were nearly broken. Replaced the battery snap. Reterminated nearly every wire because the connections had been stressed from years of attempted repairs.
Used a wire brush and sandpaper to remove a heap of battery corrosion, then repainted the battery compartment.
Replaced the jack nuts and washers, missing base plate screws, and removed a tiny amount of corrosion from the inside face of the base plate. This is the finished product.
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Edited by - Laurie on 06/03/2009 13:30:34 |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 06/03/2009 : 16:30:15
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Hi Laurie
Well Done
Nice work - Like always, your typical high standard.
Thanks for sharing all your repair info.
Regards Dr. Bob
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uJochi
Copper Member
South Africa
3 Posts |
Posted - 06/03/2009 : 17:00:04
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Looks great! Wish I could say the same for my pedal 
I got it used, wasn't working but I had read that they were an easy fix most of the time, either the Zener or the 78L05.
My pedal turns on, everything functions correctly, LED lights up when it should, there is only ever a clean signal coming out of the outputs at all times, though. Is it the C34 that needs replacing?
I must have read this entire forum! Haha, you guys are brilliant
Edit: My pedal is the DD-3 version 2b |
Edited by - uJochi on 06/03/2009 17:01:03 |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 06/03/2009 : 17:06:01
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Hi uJochi
Welcome to the forum from Australia.
You might want to upload some close up pics. (both sides)
Do you know what might have happened to it before it failed.
Or any other info/history you can remember to tell us, it all helps.
Regards Dr. Bob |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/03/2009 : 17:08:04
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quote:
Originally posted by uJochi
My pedal is the DD-3 version 2b
Unfortunately, there is no known schematic for the V2b so you're flying blind with that one.
The way I'd go about it is to use a scope to trace the signal through the pedal - I fixed my dead V3 that way. I found the output opamp was dead. (no schem available for the V3 either). |
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uJochi
Copper Member
South Africa
3 Posts |
Posted - 06/03/2009 : 17:12:09
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Hello Dr. Bob 
I will have to track down a camera and upload some pics when I can. Everything on the board looks fine, from what I can see.
I don't know what happened to it at all, I was told it was working before I bought it  If I can't fix it I'm just going to take it back, but I bought it about 2 hours away from where I stay, which is why I'm trying to see if it's fixable fairly easily.
Unfortunately I have no soldering iron skills or electronics knowledge, although from just reading this forum I kind of know what's going on. It seems like a very common problem, but I have never seen a post detailing the success of fixing a pedal with this problem, which makes me worry.
The person who I bought it from had more than one for sale, I think I should go shout at him and get a working one, damn rival that he is. |
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Mesjoggah
Gold Member
Netherlands
595 Posts |
Posted - 06/03/2009 : 17:23:13
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 i can't wait for my 'new' broken DD-3 to arrive...
To my opinion the DD-3 is the most faulty boss effect pedal out there! |
Edited by - Mesjoggah on 06/03/2009 17:24:24 |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 06/03/2009 : 17:23:23
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Hi uJochi
Apologies to Laurie for hijacking his excellent repair DD-3 repair thread
uJochi
Can I suggest you start another thread, & not use this one.
quote:
Originally posted by uJochi
Hello Dr. Bob
-- edited ---
Unfortunately I have no soldering iron skills or electronics knowledge, although from just reading this forum I kind of know what's going on. It seems like a very common problem, but I have never seen a post detailing the success of fixing a pedal with this problem, which makes me worry.
The person who I bought it from had more than one for sale, I think I should go shout at him and get a working one, damn rival that he is.
Hi uJochi
I know it's a long drive, But I wold go with the last option,
as he could then say that it was you that stuffed it up.
Make sure you test the other one before you leave.
So you know it's working.
Take a guitar - amp some leads & a good 9V battery, & plug pack in case.
Or ask him to mail it to you, considering it's not working.
Then you could mail this one back, it would save you the drive.
And do it before he has a chance to sell the other one
Good luck.
Regards Dr. Bob |
Edited by - Dr. Bob on 06/03/2009 17:31:03 |
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Topic |
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Dead DD-3 long-chip - resurrected
