Damage from DC power supply?

Mark Herrick · Post by **Mark Herrick** » 15 Apr 2005 1:22 pm

What kind of damage, if any, could I expect from applying a 10VDC power source to a piece of equipment meant to take a 10V / 7.5VA AC power source?

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Jon Light (deceased) · Post by **Jon Light (deceased)** » 15 Apr 2005 1:23 pm

Not that you would ever make such a mistake....

Mark Herrick · Post by **Mark Herrick** » 15 Apr 2005 1:26 pm

Of course not...just checking...FZZZZAAP!

Jon Light (deceased) · Post by **Jon Light (deceased)** » 15 Apr 2005 1:31 pm

I had been planning to consolidate some power supplies or maybe buy a high end power DC brick type thing. I just recently checked one of the effects that was part of this plan and discovered, in time fortunately, that it was 12V ac, not dc. That would have been a bummer. How much of a bummer depends on someone answering your question. I'm curious to know also.

David Higginbotham · Post by **David Higginbotham** » 15 Apr 2005 3:53 pm

Serious damage will result! The unit will also not operate properly.
Dave

jim milewski · Post by **jim milewski** » 15 Apr 2005 5:04 pm

my guess is no damage, it will pass through the bridge and the unit may perhaps even possibly work....let us know

Ray Minich · Post by **Ray Minich** » 15 Apr 2005 7:02 pm

I'd hafta agree that probably nothing should go wrong if the next stage after the input is a rectifier. 10VAC would be about 14 volts peak to zero, and the 10 V DC would be like only applying one side of the waveform. If the input stage after the power supply is another transformer though, it will then depend on how long the wrong power was applied. Your chances are 50:50.

David Higginbotham · Post by **David Higginbotham** » 15 Apr 2005 7:57 pm

I actually read the question backwords which would be using AC for DC equipment. Better read with my glasses next time! I would still go on the safe side and not risk it tho.
Dave

Bill Crook · Post by **Bill Crook** » 16 Apr 2005 3:45 am

DON'T EVEN THINK ABOUT IT !!!!!!

Take it from someone who's been there,done that,and the results arn't good at all.

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http://home.comcast.net/~crookwf/
http://photobucket.com/albums/v479/billcrook/

Steinar Gregertsen · Post by **Steinar Gregertsen** » 16 Apr 2005 4:52 am

.....using AC for DC equipment.

I - from now on just known as Stupid Steinar - accidentally did just that a few days ago.

Result,- my favorite delay, the Line6 Echo Park, is trashed........

Stupid Steinar

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www.gregertsen.com

[This message was edited by Steinar Gregertsen on 16 April 2005 at 05:53 AM.]

Mark Herrick · Post by **Mark Herrick** » 18 Apr 2005 12:19 pm

I think I fried a Midiverb II.

The original power supply (wall wart) died and I neglected to check whether it was AC or DC. Plugged a DC into it and got nothing. Then noticed that it was supposed to be AC.

The jack on the back of the Midiverb says 9VAC; the Alesis wall wart is 10VAC / 7.5VA.

The closest replacement I found locally was 9VAC / 1A.

Now all I get is hummmm...

Could the difference in the current ratings be making any difference? It's hardly worth the effort and expense to send it to Alesis for repair...

John Daugherty · Post by **John Daugherty** » 19 Apr 2005 4:30 am

Mark, If the internal rectifier circuit is half or full wave(not a bridge circuit),polarity is important when you connect a dc supply.
My guess is, you will find one or two diodes and an maybe an electrolytic capacitor fried. If you replace them, it should not be expensive(less than $10).
Without going into detail; connect an ohmmeter across each diode(connected inline with the power-in socket). If the resistance is less than 10 ohms in either direction, replace it. Do the same for the electrolytic capacitor.
Let me kow what you find. We will fix that rascal........JD

Joey Ace · Post by **Joey Ace** » 19 Apr 2005 5:17 am

I did this to my Kurtzweil Micro Piano. No damage.

I use an M-Audio Midi keyboard with it. The keyboard takes 9 VDC, the Micro Piano takes 9 VAC. The power supplies look the same and have identical plugs.

The unit did not work, I discovered and corrected the error within a minute.

I suspect some equipment is designed to be more idiot-proof than others. I was lucky.

I labeled both supplies with BIG WHITE Tape, so this will never happen again.

Jon Light (deceased) · Post by **Jon Light (deceased)** » 19 Apr 2005 11:29 am

I suspect some equipment is designed to be more idiot-proof than others

I take pride in exceeding in pure idiocy any high fallutin' idiot proofing out there.
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I love the smell of burning electronics in the morning..........

[This message was edited by Jon Light on 19 April 2005 at 12:35 PM.]

Mark Herrick · Post by **Mark Herrick** » 19 Apr 2005 12:22 pm

Robert Duvall is such a great actor...

On to the case at hand:

I opened the Midiverb and it's kind of hard to see where all the circuit board traces go after the power input jack, but I think I can see, in this order, two 25V/330uf capacitors, five diodes (I guess; they are small, like a resistor, black, with a silver band at one end, and marked ZM IN 4002 729), then there are two more 25V/330uf caps, two 16V/1000uf caps and lastly two more 16V/1000uf caps.

If you think the little black things are the diodes, I'll check those with a multimeter...

Looks complicated to me though...

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Jon Light (deceased) · Post by **Jon Light (deceased)** » 19 Apr 2005 12:35 pm

Yep--IN 4002 sounds like a diode to me.

Mark Herrick · Post by **Mark Herrick** » 19 Apr 2005 12:55 pm

Sounds more like part of a campaign slogan to me...

Tippecanoe in 4002!

Jim Peters · Post by **Jim Peters** » 19 Apr 2005 1:58 pm

I have fixed many devices that have been incorrectly powered, check all those diodes and the capacitors too. Good luck, JimP

Mark Herrick · Post by **Mark Herrick** » 19 Apr 2005 2:16 pm

How do I check the capacitors?

I checked the diodes (?) near the power jack; the five I mentioned earlier.

With the meter set to 20K Ohms (or any other range) the reading starts low (sometimes even negative) and then climbs until it exceeds the range. It does the same with the probes reversed.

I found one other diode slightly further from the power jack. Can't get any reading from it in any range. It is kind of clear/copper colored with a black band on one end.

I found four other diodes on the opposite end of the board. On the 20K Ohm range two of them (copper colored) stabilize at 4.8, one (silver with a black band) stabilizes at 10.4 and one (copper colored) doesn't read anything.[This message was edited by Mark Herrick on 19 April 2005 at 05:17 PM.]

Dave Grafe · Post by **Dave Grafe** » 19 Apr 2005 8:37 pm

The diodes should read low resistance in one direction and very high resistance in the other. It's particularly hard to get readings on components when they are still in the circuit, though, as you are now seeing - the climbing resistance is a result of capacitors in the circuit charging up, most likely they are good if the reading goes entirely off the end of the highest scale.

Reverse the polarity of the probes and re-check the diodes. If the reading does not change you most likely have a bad puppy.

Unfortunately, this is a WAY over-simplified explanation, but it's a start.[This message was edited by Dave Grafe on 19 April 2005 at 09:41 PM.]

Paul Osbty · Post by **Paul Osbty** » 19 Apr 2005 10:55 pm

Why not just try the correct power supply? Most all of the Alesis rack units take the same supply. A music store must have one you could try.

Also, 1A doesn't sound like enough juice to power that up. The hum you hear may just be that 1A supply underpowering the Alesis.

Use a Diode Check mode to check diodes. It's the only way to check the junction.

Mark Herrick · Post by **Mark Herrick** » 20 Apr 2005 10:13 am

Why not just try the correct power supply?

Occam's Razor?

Another friend of mine suggested the same thing about the 1A current maybe being insufficient.

The unit is only worth about $60 so I may be finished digging around in this thing for the time being...

Thanks for the suggestions.

John Daugherty · Post by **John Daugherty** » 20 Apr 2005 11:09 am

You need to check the diodes with an ohmmeter set to the Rx1 scale. Some cheap meters do not have this scale. With the leads connected one way, it should read ~15 ohms. connected in the opposite polarity you should read nothing (out of circuit). Normally, a bad diode is shorted and will read zero ohms in either direction.
A bad capacitor,damaged by overvoltage is also usually shorted (zero ohms).
With your meter on the 20k range, any resistance below 1k can appear as a short. You must use a meter on the Rx1 scale.

Paul Osbty · Post by **Paul Osbty** » 20 Apr 2005 1:29 pm

"You need to check the diodes with an ohmmeter set to the Rx1 scale"

I won't belabor this, but that's erroneous information. Especially when checking a diode in circuit. Diodes are not measured in ohms.

John Daugherty · Post by **John Daugherty** » 20 Apr 2005 5:12 pm

Paul, that is not erroneous information. I work on equipment daily, Spent several years in elex schools. I am very good at what I do. One thing I do is check diodes on a daily basis while troubleshooting electronic equipment. I have been an electronic technician for 47 years.
The test procedure given, is in basic laymans language in hopes that I can help someone locate a problem without deciphering a lot of fancy terms.
When an analog ohmmeter on the Rx1 scale(1.5vdc) is connected across a good diode,in the forward direction it will show ~15 ohms.