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ununtrium
Bronze Member
Germany
84 Posts |
 Posted - 05/30/2006 : 17:34:56
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Hi there!
I have got a technical problem with a DM-2 I got in the mail today. I have it on a daisy chain in my BCB-60. When it is properly connected, the LED does light up nice and strong. When I twiddle the knobs, I got some reaction from the "repeat rate" knob, but otherwise nothing, no signal whatsoever. I opened it up and took a look around, but I did not know what to look for. I noticed no loose cabels or the like, but that does not mean much.
What could be the problem? Is there something I overlooked, when connecting the pedal? Any help would be greatly appreciated.
Thanks! |
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stahlhart
Platinum Member
1318 Posts |
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stahlhart
Platinum Member
1318 Posts |
Posted - 05/30/2006 : 19:13:07
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A bit of general information about analog delay circuits: what happens is that you feed an audio signal in, then it's split between a "dry" path and a "wet" path -- the dry signal is the original, unmodified signal, and the wet path is delayed/modulated, and then remixed with the dry signal; that's where the delay effect comes from.
So you should see something like that happening in a DM-2. It looks to me that the signal is split after one half of IC1 (a 4558 dual op amp), and then remixed at the output through the other half of the same IC. So immediately I become suspicious about the health of that guy, if you are stating that you get nothing in the way of output from the pedal in either mode.
(edit: my other suspicion would be Q1, as it more or less has its ass hanging out by the input jack, and could possibly take a transient hit there)
edit again: The more I think about it, the more suspicious I am of Q1 -- if you're stating that you get some sort of reaction from the repeat rate control, it almost sounds to me like some internal circuit noise is leaking through, and you're tweaking it with the control, but there's no audio signal getting through at all -- there don't appear to be any overall power issues, as you've got the LED switching on and off with the foot switch normally. If there were some sort of residual charge on the center conductor of a cable connected to the input, it could have discharged through Q1 and damaged it. Many years ago I damaged a Commodore 64 computer this way -- it has an analog synthesizer that feeds a transistor driver which then outputs through a DIN jack, and I was goofing around one day and decided to connect it to a Fender Twin and run the sound from computer games through the amp with effects -- and that POP you usually get when you plug a cable in apparently was enough to fry that transistor in the C-64... it was a simple repair, but the lesson was to never do that again with everything powered up.
Here's the C-64: http://www.freeinfosociety.com/electronics/schemview.php?id=1468 -- look for Q8 on the diagram, and compare that to Q1 on the DM-2.
C.K.
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Edited by - stahlhart on 05/30/2006 19:37:29 |
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ununtrium
Bronze Member
Germany
84 Posts |
Posted - 05/30/2006 : 19:51:38
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Many thanks for the schematics, but I am no good at deciphering those. I get no signal in either on- nor off-mode. I get the feeling I�ve been sold a broken pedal. 
I�ll try to get my money back, but just in case the seller does not oblige, how much would you think it would be to get the pedal fixed? Maybe stinkfoot could help me out here? |
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stahlhart
Platinum Member
1318 Posts |
Posted - 05/30/2006 : 20:21:34
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That would be the guy I'd contact first, if I could not tackle the repair job on my own -- I think that you could reach Andreas through http://www.stinkfoot.se -- he has his own page off of that one.
C.K.
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ununtrium
Bronze Member
Germany
84 Posts |
Posted - 05/30/2006 : 21:46:16
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Many thanks for your trouble, stahlhart. I contacted the seller as well as stinkfoot.
It was hard enough to pluck up the courage to shell out the dow for this pedal in the first place. Imagine how frustrating it was to see it not working at all!!!  Well, let�s hope everything works out. I hope to be able to join the "Functioning Analog Delay Owners Club" soon  Again, many thanks for your help. |
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stahlhart
Platinum Member
1318 Posts |
Posted - 05/30/2006 : 22:33:07
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Good luck...  it looks like your options will be (a) keep the pedal and have it repaired, if you can do so in an manner that isn't too outrageously expensive, or (b) send it back to the seller for a refund, if they agree to do so. Not exactly a slam-dunk decision, as you might have gotten a real good deal on this one that you might not be able to match down the road...
C.K.
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bossarea
Forum Admin
United Kingdom
3652 Posts |
Posted - 05/30/2006 : 23:33:34
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You're really unlucky to have struck a faulty pedal as they very rarely fail. When they do break they're usually completely dead because someone has mixed up + and - and that makes it double unlucky.
I'm sure Stinkfoot can help you sort it though |
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ununtrium
Bronze Member
Germany
84 Posts |
Posted - 05/31/2006 : 00:35:35
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The seller just got back to me telling me he goes along with any course of action I want to take. It appears, prior to putting the pedal up for auction he had both the input and the output jack replaced by a local dealer, as the original ones had been quite corroded. Unfortunately, he did not check the pedal, before shipping it. Oh dear...! 
Do you think it would be costly to have the problems resulting from this "repair" fixed? I think ,I paid the normal price DM-2s are going for these days, so it was not exactly a deal, but on the other hand a DM-2 is a DM-2, if you know what I mean. 
Cheers  |
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stinkfoot
Silver Member
Sweden
181 Posts |
Posted - 05/31/2006 : 17:50:35
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| I'm connecting via Opera mini on my mobile, so I'll keep it short. stahlhart is most likely right. If there's no signal at all, it's probably the input/output section or the mixing stage. |
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dm-2 technical problem: no output
