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drownman
Copper Member
Sweden
6 Posts |
 Posted - 12/19/2005 : 08:57:18
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Hello all, thank you for a valuable forum.
I recently purchased a Boss DM-2, I won it on an online auction, paid around $120 for it which I understand is a good price. I got it, tested it on saturday morning at work, with a powesupply, no instrument though. It lit up, and seemed to work just fine. In the afternoon I did an unscheduled stop at my rehearsal (sp?) location to try it with my bass. I had no gear there, since I'm assembling my pedal board, but my guitar player had his. I took a voltage/polarity switchable PSU from him to try with the DM-2. (You can begin teeth grinding with agony now).
I plugged it in without checking polarity and voltage. Not a spark. After tampering and fiddling around, checking that the PSU worked, getting polarities and voltages correct, still no sign of life. The PSU was set to 7.5V, but I can't see how that could have fried anything, the big fear is that the polarities were switched so it got a positive tip. I thought Boss pedals were protected/buffered against such damage? The circuit board looks fine, there's a very light whiteish miscoloration near the edge between to circuit lines, that's the only thing i can see.
I tried with batteries and all I could think of. Now back to work, it still doesn't light up with the same equip i tried it with on saturday.
If it turns out to be fried, people at work can check it with a current meter or whatever you use, any tips on that? |
Edited by - drownman on 12/19/2005 09:00:55 |
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Goran
Double Platinum Member
Sweden
2203 Posts |
Posted - 12/19/2005 : 09:45:13
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| I would contact Stinkfoot, www.stinkfoot.se, he knows lots about Boss pedals inside. |
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drownman
Copper Member
Sweden
6 Posts |
Posted - 12/19/2005 : 15:47:22
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| Thx, maybe I'll drop him a mail. A friend has a contact who is supposed to be good at these things, I'll have him take a look at it. |
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phostenix
Gold Member
USA
754 Posts |
Posted - 12/19/2005 : 15:51:56
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If you've got people that can test it, have them check the DC voltage as you plug it in to see if the pedal is shorting the voltage. If it is, check D4, the voltage regulating zener diode, to see if it is shorted. Boss lists it as an RD11EB3, which should be an 11v zener.
If the input voltage is not being shorted, then we move on to checking other places for voltage. Let me know what you find.
Grace and peace. |
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stahlhart
Platinum Member
1318 Posts |
Posted - 12/21/2005 : 17:35:48
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Should D1 (1S2473) also be checked?
Looks to me like this might be there to protect against an AC adapter with reversed polarity. (?)
Not much else to the power supply circuitry, apart from this and the Zener phostenix mentioned...
C.K.
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phostenix
Gold Member
USA
754 Posts |
Posted - 12/21/2005 : 20:03:00
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It's purpose is to make your LED dim.  It and the resistor in series with it reduce the voltage slightly from the ac adapter. In the older pedals the resistor was larger which is why the LED is dim when you try to use an old pedal with a Boss PSA adapter.
If that diode opened, it would stop the pedal from working on an ac adapter, but it would still work on a battery. It it were shorted, you wouldn't even notice it was gone.
The zener will also protect against polarity reversal from either the ac adapter or a battery.
Grace and peace,
Steve
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stahlhart
Platinum Member
1318 Posts |
Posted - 12/21/2005 : 21:12:35
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phostenix:
Thanks VERY much for the clarification! Learned something new today... 
So it does look as though we'd have to check that Zener diode first (or at least make sure that the B+ coming off of the DC filtering is there).
C.K.
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phostenix
Gold Member
USA
754 Posts |
Posted - 12/21/2005 : 22:03:29
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If you were to plug in a 9v ac adapter, D1 will half-wave rectify it. So, it has a purpose there, also.
The "problem" with this diode and resistor in series with ground protection scheme is that it can easily be defeated by the user leaving the zener to fend for itself. Here's the situation: The "ground" of the pedal that the circuitry sees is now .5 or .6V above the ground connection on the input jack. If you have a power supply with multiple outputs that you connect to your pedals AND at least one of your pedals in not a Boss pedal with the diode and resistor in series with the ground connection (or a Boss ME-50 which is what I typically have connected), the negative lead of the power supply gets "shorted" to the ground of the guitar cable, which bypasses the protection diode and resistor. That's why the LED's on older pedals are brighter in this configuration.
There are alot of posts on the internet about this ACA vs. PSA adapter business that explains all of this in detail if you want more.
Grace and peace,
Steve
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Edited by - phostenix on 12/21/2005 22:05:25 |
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drownman
Copper Member
Sweden
6 Posts |
Posted - 03/03/2006 : 15:51:41
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| Well, after a long time here's an update. A friend at work took it to a maintenance-of-amps-gizmos-and-pedals guy, and one of the delay circuit chips was fried, don't know which. But he ordered the part and now it's fixed, just haven't gotten it back yet. At the price (lparts + labour) of �85, luckily I got the pedal for �100, so I guess that lands at a normal price for one of these :) |
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Have I fried my DM-2?
