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tony
Bronze Member
United Kingdom
142 Posts |
 Posted - 08/12/2008 : 15:03:07
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OK, so yesterday I posted a "Hello everybody" thread along with a general query about whether it's necessary to replace electrolytics in 25 year old pedals as a matter of course. After posting that, I went to play around with my DD2 and, almost on cue, it's developed some serious problems - so I deleted that post out of frustration!!
I got the pedal about a week ago in very near mint/barely used condition. It was absolutely fine at first. The problem(s) are as follows:
The pedal powers up fine, but the effect is inaudible on any but the most extreme settings and even only barely audible then.
After having a quick peek inside to see if there was anything really obvious, the pedal didn't power on at all and seemed to short out any power source (diago switchmode power supply went into overload mode and the new battery I tried got extremely hot extremely quickly). I think this was the foil shield inside shorting out the dc supply board - I must have dislodged it during my peek.
Anyway, I adjusted that and now it's back to the original weak/non existent effect problem. I don't mind technical answers, I can cope with the electronics and am interested in learning as much as possible. Oh, and any help will be massively appreciated!!! |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/12/2008 : 16:22:19
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Hi tony and welcome!
The symptoms you describe could have a large number of causes, so some questions to maybe narrow it down.
1) Does this happen on both the power supply plus a known good battery?
2) Is the uneffected signal (LED off) full volume? Any issues with this signal - distortion, etc?
3) Is the LED at full strength when the effect is on?
4) Inside the pedal there is a 78L05 regulator (IC10). Is it getting hot? Can you measure the voltage across C49? Is it 5VDC?
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 08/12/2008 : 17:24:16
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Hi tony
Welcome to the forum from Australia.
I did notice that you had posted & deleted your post yesterday.
Was the DD-2 working when you bought it?
Did anything like reverse volts happen to it?
Are you using a PSA or regulated 9V adapter?
Be aware that the DD-2 - DD-3 have a turn on delay before the red LED comes on, when it's turned on for the first time.
It does some kind of System check on the 12 Bit DSP.
Some people mistake this as a faulty pedal.
IF you have a shorted pedal it's typically D6, if I remember correctly.
And as Laurie wrote, check the 78L05 (T0-92) package sized 5V 3 pin regulator.
If you don't already have a schematic, you can get one from:
http://www.freeinfosociety.com/electronics/schempage.php?cat=1
and a few other places.
Please keep us informed with your progress.
Regards Dr. Bob
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/12/2008 : 17:33:23
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Thanks for replying!
1). Running the unit on a fresh battery produces nothing - no LED, no bypassed signal.
2). The adaptor powered uneffected signal is fine - identical to a direct signal.
3). Sorry, possibly owing to the maze of wires I'm finding it impossible to locate this IC. Where is it? The one right next to C49 (which, going by the schematic is where I thought it should be) is the BA634.
4). C49 is consistently at 10.2v, not 5v (!).
EDIT
Just found IC10 - it's the one marked IC10 on the board - duh.
Doesn't seem to be getting hot.
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Edited by - tony on 08/12/2008 17:39:42 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/12/2008 : 17:42:56
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| C49 at 10.2V is certainly a problem. Looks like IC10 is fried - it is a 5VDC regulator. Just to be sure, check the voltage from the pedal case to all three legs of IC10 and let us know? Thanks! |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/12/2008 : 17:51:10
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Hey Dr Bob,
It was working fine when I got it. At first.
I'm assuming reverse volts is incorrect polarity? Couldn't have happened at any time. I've been using a Diago switching PSU which is quite a popular power supply in the UK. There's also a BOSS PSA 240 on the way.
How do I check D6? |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/12/2008 : 17:56:51
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Right. IC10 reads 19.7v going in, 0v to ground and 10.2v out.
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 08/12/2008 : 17:59:19
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quote:
Originally posted by Laurie
C49 at 10.2V is certainly a problem. Looks like IC10 is fried - it is a 5VDC regulator. Just to be sure, check the voltage from the pedal case to all three legs of IC10 and let us know? Thanks!
If you don't have a 78L05 you can temp. use a standard 7805, with some short wires soldered onto the legs & then into the PCB, to test it out
and 7805 can be easier to find than 78L05's, at least till you order some.
Check the protection diode/zener as well.
Sounds very much like the pedal got a belt of REVersed volts.
And it's probably a good idea to replace the filter cap, as well if it was Rev. Volts.
Good night Tome, Laurie & guys, it's Zzzz time fro the old Doc.
Regards Bob |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/12/2008 : 18:27:38
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Thanks Doc!
19.7V is WAAAAAAY too high for a pedal. Not sure what power supply you are using, but I'd highly recommend taking it off and chucking it away. 9VDC regulated is the recommended supply.
With 19.7V measured on IC10, it is a certainty that D6 is also blown. Replace it with a 1W zener. 11V is the nominal zener voltage, but I use anything from 11 to 13 volts with no problem (hence the certainty that D6 is blown - if it wasn't the incoming voltage would be clamped to 11VDC).
Replace D6 and IC10 and you should be back to 5VDC across C49. Once that's done, we can explore what was damaged bu the over-voltage - we must hope that the long chip isn't dead from the overvoltage or the pedal is a throw-away.
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/12/2008 : 18:35:37
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I just had a thought... there isn't something on your meter that is making it read exactly double the actual voltage is there? Some sort of "calibtate" mode or a voltage dividing probe??
19.7V in to 10.2V is exactly double what I'd expect it to be (9V in to 5V)
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Edited by - Laurie on 08/12/2008 18:35:59 |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/12/2008 : 19:24:25
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Laurie, you're right!
I just had exactly the same thought - I was reading directly out from the PSU just to check what was coming out of it and got a double voltage, then I tried another 9v PSU and got the same!!
Please excuse the novice.
Please note the unit runs off a battery now - I guess that may have been the switch being temperemental through lack of use. Or something else.
The actual voltages running off a fresh battery are:
9.47v going into IC10 and 5.67 coming out and across C49.
Something I've noticed. Sometimes when I check IC10, a sine wave like bleeping noise happens which echoes in the same very weak way a guitar signal does. |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/12/2008 : 22:33:34
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Ignore that sound - it's something to do with grounding as it doesn't happen when the back cover is on.
Anyway, have noticed something interesting. D3 from the de-emphasis/mixer section only passes between 0v and .04v, when according to the schematic it should be on the 5v supply.
EDIT
Yup, definitely an blown diode there - no continuity. Will replace that tomorrow. Gonna do something else now, I think.. |
Edited by - tony on 08/12/2008 22:55:00 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/12/2008 : 23:53:40
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| Right you are. Let me know when you are ready to have a crack at the loss of signal. |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/13/2008 : 14:30:00
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The situation as it stands:
The pedal powers up fine, passes signal. All mode and delay time controls react as normal. The weakness of the effect means you never hear more than about two repeats and even then only barely. The feedback and effect level controls are working fine - the pedal just isn't producing much in the way of delay. I carefully replaced that zener diode with the correct 5.1v part but there doesn't seem to be much voltage going across it anyway. |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 08/13/2008 : 14:53:39
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quote:
Originally posted by tony
The situation as it stands:
The pedal powers up fine, passes signal. All mode and delay time controls react as normal. The weakness of the effect means you never hear more than about two repeats and even then only barely. The feedback and effect level controls are working fine - the pedal just isn't producing much in the way of delay. I carefully replaced that zener diode with the correct 5.1v part but there doesn't seem to be much voltage going across it anyway.
Hi tony
There seems to be some misunderstanding, the protection Zener is 11V not 5.1V.
It's the 78L05 regulator that's 5V.
If you have a 5V zener feeding the 5V regulator, that won't work.
You need a differential of at least 2V or greater.
Besides the 9V is tapped off before the regulator, & runs to other parts of the circuit, which would now only have 5VDC on them, like the opamps.
Or have I misunderstood which part, or what you have done-repaired?
Regards Dr. Bob
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/13/2008 : 15:08:19
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Hi Dr. Bob - I think he is talking about D3 (the LED zener). tony, this looks important on the schematic, but it doesnt affect the sound at all.
Some deduction:
- we know the un-effected sound is OK, so IC1a (the output mixer) is OK.
- we have echos, so the digital part of the circuit is *probably* OK
Do you have any way of checking for a signal across R44? A scope would be ideal... This will tell us if there is proper signal getting to the expander. |
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DD 2 problems
