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Using the wrong power supply... what can happen?
Old 2nd May 2014
  #1
Gear Nut
 
Doc Asbury's Avatar
 
๐ŸŽง 10 years
Using the wrong power supply... what can happen?

Here's a very newbish electronics question but the answer should be helpful to many folks.

I just picked up a Wohler ARS-21B audio switcher on ebay. It's just a simple 10ch in, 1ch out signal router. It did not come with a power supply. And here's the problem:

The back of the unit, as well as the introduction in the owner's manual, state that it takes 24VAC, 35W. But if you read the manual, it mentions *twice* that it takes 24V DC. So we have a misprint somewhere, and I don't know which is correct.

My question, and this applies to all sorts of gear, is what happens if we plug in the wrong power supply to test a piece of gear? Specifically, if I plug a DC power supply into a unit that takes AC, what will happen? And vice-versa.

I seem to recall accidentally plugging an AC power supply into a piece of DC gear once, and whether it was due to that blunder or not, that gear never worked again.

Are there any electronics techs out there who can shed light on what's ok, not ok, and very not ok?

P.S. If you're interested, here's the Manual for the Wohler ARS. Note on page 4 and in the following diagrams it specifies "24V AC". But on page 15 and again on 16 it says "24V DC". I have a 24V DC power supply which I could test it with, but I wanted to ask you guys before potentially damaging anything.
http://www.wohler.com/LinkManuals/ARS-22A.pdf
Old 2nd May 2014
  #2
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Lotus 7's Avatar
 
1 Review written
๐ŸŽง 10 years
Check with the company to confirm the correct supply. Using an AC supply with a device expecting DC will almost certainly damage the device. Using a DC supply with a device expecting AC may cause damage to the device, it may do nothing (depending on the input circuit of the device, or if the device uses a transformer input power circuit, it may damage the power supply itself).

Since there is an obvious typo in the various documentation, you must determine which specification is correct. The chances are 50-50 that you will be wrong and something will be damaged. You're playing Russian Roulette with a cartridge in every other chamber.

Contact the company and get the correct answer.

It's "very not OK" to proceed with a trial and error approach, because the likelihood of doing serious damage is very high.

The manual (pp.16) states: "Plug in the supplied external AC to 24VDC power supply into the connector to supply power to the ARS unit". I'd tend to believe the published manual, and running the switcher on 24 VDC makes more sense than running it on AC, but because you have documentation that also mentions an AC supply, you have to confirm which is correct.
Old 2nd May 2014 | Show parent
  #3
Gear Nut
 
Doc Asbury's Avatar
 
๐ŸŽง 10 years
Thanks Lotus. Yeah I'm also leaning toward believing the "24V DC" part, especially since I have a different piece of equipment made by Wohler which takes 24V DC. I was very tempted to just plug it in, but you brought me to my senses... I may have to wait a day for the company to respond, but it'll be worth it to avoid potentially blowing anything up. I'll post their response for anyone who buys the same gear.
Old 2nd May 2014
  #4
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jaxman12's Avatar
 
๐ŸŽง 5 years
Also note about power supplies:

You must use the correct voltage. ie, a 12volt DC may not be used on a 5volt DC or 9volt DC, or 24volt system. Therefore, 12volt with a 12 volt system, 9volt with a 9volt system, etc.

You may use a higher amperage on your system, but not less amperage than the system is rated. example, If a system requires a 12volt 1amp power supply, you may use a 12volt 2amp power supply but not a .5 amp(500milliamp) power supply .

Observe polarity on the + and - connections.
Old 2nd May 2014
  #5
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1 Review written
๐ŸŽง 10 years
Yes, Wohler needs to hire a copy proofreader who's wider awake. The manual "pdf" is marked "Rev. B," so a glaring error such as different PS specs on different pages should have been caught.

Interestingly, the Wohler website has a currently posted block diagram (attached below) of the ARS-22A which shows a 24 VAC supply!
I'd hold off connecting anything until you get a definitive answer (hopefully in writing) from them.

However, digging a little deeper, although there is not a schematic in the manual, there is a circiuit description:

[I]"Analog Switch and Button Backplane PCBs Since a single-sided 24V supply is used, all op-amps are โ€œbiasedโ€ with a 1/2 supply reference. The CMOS devices are powered from a separate zener-regulated 18V source on each analog switch and backplane board. The analog switch elements are in series with an opamp summing junction, so they can handle very high input signal levels without any "breakthrough" effect.[/I]"

That wording, especially the "single-sided 24V supply" and "all op-amps are โ€œbiasedโ€ with a 1/2 supply reference" certainly implies a DC power source, but of course, that could be from a rectifier/filter inside the unit.

Hopefully, someone at the factory can confirm the correct supply type. Otherwise ask them to send you a complete schematic and it will be obvious if the device includes a rectifier and filter to create the required DC for the CMOS switches and the op amps.
.
.
Attached Thumbnails
Using the wrong power supply... what can happen?-ars-22a-block-diagram.jpg  
Old 4th May 2014
  #6
Gear Nut
 
Doc Asbury's Avatar
 
๐ŸŽง 10 years
Hey Jaxman, great info. I've often wondered what the rules are about amperage, especially with regard to using more than required.

Lotus, brilliant detective work. It turns out you're correct that the circuitry requires DC, but on my model there happens to be a rectifier inside the unit. The Wohler rep ended up getting back to me within a few hours with the info below. What he told me, along with your suggestions, prompted me to pop the hood and take a look.

Quote:
If the back of the unit says"24VAC" then it's probably correct. Some of the early units did take AC. These had a power supply board inside as a DC supply for the unit. The later ones took a DC wall-wart, and the manuals were not always correctly updated to reflect the change.

The best way to tell is to pull the lid on the unit and see if there is a DC power supply board in side. It'll have the usual diode rectifiers and filter caps you'd see on any such board. If that's the case then you need an external AC transformer for it.

We don't have those anymore but I've attached a copy of a web page for Condor Electronics who still has these available.
Attached are some pics of what I found.
(1) The unit itself.
(2) The back which is clearly labeled "24VAC".
(3) What looks like the DC rectifier/filter board mounted inside.

So mystery solved, I think! The early units like mine (s/n 46242) require a 24VAC external power supply. Later units (Rev. B you pointed out in the manual?) got rid of the internal power board and started using DC external supplies. The manual was a mosh of both. Who knows if this specific info will be useful to anyone else for this obscure piece of gear. But I do see them pop up on ebay, almost always missing their power supply.
Attached Thumbnails
Using the wrong power supply... what can happen?-ars-21b-012.jpg   Using the wrong power supply... what can happen?-ars-21b-001.jpg   Using the wrong power supply... what can happen?-ars-21b-003.jpg  
Old 4th May 2014
  #7
Lives for gear
 
๐ŸŽง 15 years
looks like 24vac to me.

the bridge on the riser card gives it away.

plus they would not misprint the outside of the unit.
Old 4th May 2014
  #8
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1 Review written
๐ŸŽง 10 years
Yep, 24 VAC it is. that's a rectifier and filter board. It would not have those components if it used an outboard DC supply. A printing error on a spec sheet is not very good, it does happen. However a printing error on the power connector would never be allowed into production by any sane manufacturer. Just get a 24VAC 2 Amp transformer wall wart, and you'll be good to go. Nice that they at least included a slo-blo fuse inside.

Also interesting that the rectifier/filter board looks like an "add-on". I wonder if they didn't first design the switcher for DC and they decide later to use a AC outboard transformer.

It's almost criminal that a manufacturer should cause so much confusion by publishing conflicting specs, and producing (2) versions of the same device using different power supplies, but obviously it does happen. They should have changed the model number when they switched from the AC to the external DC supply.

I guess they always expect the original, supplied power supply to be with the device forever.

Good that you waited before connecting a DC supply.

With the transformer-less, rectifier/filter circuit inside, connecting a DC supply would have actually gotten current through the bridge, but would not have produced the peak voltage the regulator needs. It's unlikely it would have caused any damage at all, but the switcher may not have worked properly, because the internal DC power rail voltage would probably have been a little low.
Old 4th May 2014
  #9
Gear Nut
 
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๐ŸŽง 10 years
Cool, thanks for the confirmation guys! I suspected "BRG1" printed above the funky black box meant it was a rectifier bridge, but I wasn't sure.

As an interesting footnote, there's another Wohler ARS unit on ebay which, like mine, says "24 VAC", but someone scratched it out and wrote "16V DC" and is selling it with a DC power supply.
http://www.ebay.com/itm/231197288984
I messaged them to ask about that, and they said the previous owner modded it. Now that I think about it, that would probably be easy enough... just rip out or bypass the add-on power board. I guess someone didn't feel like buying an AC adapter. Tempting... but I think I'll just keep it the way it is & wait for the replacement AC.

Thanks again, I don't know about anyone else reading along, but I just learned a whole lot about power supplies in this thread.
Old 5th October 2018
  #10
Here for the gear
burned my Technics piano

Hi folks,
I am new here, really need some help with this issue please. The thing is I am getting really into music lately and doing some production now that im in my mid 20s ... so I have this nice piano my dad bought me a long time ago when I was a kid and its a TECHNICS SX-PX222. Unfortunately it burnt some time ago because of connection with wrong voltage.

Power source is 120V but was connected into 220v and burnt.

Can it be fixed? someone told me I had to change the card, but I not quite understand. What should I look up? a repair for the "card" on ebay?

just trying to find some help somewhere on the internet about this. appreciate it
Attached Thumbnails
Using the wrong power supply... what can happen?-2ccd6386-ca89-4df8-b92e-795fc551e579.jpg  
Old 6th October 2018 | Show parent
  #11
Gear Guru
 
๐ŸŽง 20 years
Quote:
Originally Posted by shank91 โžก๏ธ
Hi folks,
I am new here, really need some help with this issue please. The thing is I am getting really into music lately and doing some production now that im in my mid 20s ... so I have this nice piano my dad bought me a long time ago when I was a kid and its a TECHNICS SX-PX222. Unfortunately it burnt some time ago because of connection with wrong voltage.

Power source is 120V but was connected into 220v
yikes
Quote:
and burnt.
as in smoke and flames came out?

Quote:
Can it be fixed?
I know I would toss it.

Quote:
someone told me I had to change the card, but I not quite understand. What should I look up? a repair for the "card" on ebay?
If you are experienced at electronic repairs, you might be able to replace the power supply yourself (if you can find one),... but who knows what else got damaged in the "fire"? You could fix the power supply only to find out there was a lot more damage 'downstream".

Quote:
just trying to find some help somewhere on the internet about this. appreciate it
You could find someone local who does repairs of this kind. You can bring the keyboard to him and have him give you an estimate. Most guys will charge you something just for looking at it. Even if the bench charge gets 'applied' to the final cost, it may not be worth the money, especially if it is an old obsolete keyboard.

Look up your model on eBay and Reverb see what another keyboard of the same type is actually selling for. It might very well be less than ordering the spare parts for this unit, never mind the labor.
Old 6th October 2018
  #12
TSM
Gear Addict
 
TSM's Avatar
 
๐ŸŽง 15 years
First I would see what the damage looks like and post a pic here . Obviously make sure it's unplugged, then take out the 4 screws at the back top of the piano behind the music rest. The top will then slide forward and up. This will reveal the different boards of the piano. There will be the transformer, power board, main board/amp board.
Let us know how u get on.
Old 8th October 2018
  #13
Here for the gear
Thanks for the words guys. The piano wasn't burnt like in flames and fire kind of style haha. It was just plugged to the wrong power voltage without using a converter.
So I guess something inside can be changed and replaced right? I just want to know the name of that piece to find a replacement on a local store or maybe on ebay.

cheers!
Old 8th October 2018
  #14
Here for the gear
Thanks for the words guys. The piano wasn't burnt like in flames and fire kind of style haha. It was just plugged to the wrong power voltage without using a converter.
So I guess something inside can be changed and replaced right? I just want to know the name of that piece to find a replacement on a local store or maybe on ebay.

cheers!
Old 8th October 2018
  #15
Here for the gear
Thanks for the words guys. The piano wasn't burnt like in flames and fire kind of style haha. It was just plugged to the wrong power voltage without using a converter.
So I guess something inside can be changed and replaced right? I just want to know the name of that piece to find a replacement on a local store or maybe on ebay.

cheers!
Old 8th October 2018
  #16
TSM
Gear Addict
 
TSM's Avatar
 
๐ŸŽง 15 years
As you probably know, Technics pianos are no longer made and parts have been discontinued. However the PS will use generic parts in general so it should be able to be repaired. There is no card you can buy to put into make it work...you would need to get a repairer to have a look. If you posted a picture, it maybe obvious as to the extent of the damage...
Good Luck!
Old 8th October 2018
  #17
Gear Guru
 
๐ŸŽง 20 years
Quote:
Originally Posted by shank91 โžก๏ธ
Thanks for the words guys. The piano wasn't burnt like in flames and fire kind of style haha. It was just plugged to the wrong power voltage without using a converter.
If it doesn't work now, something inside is fried, though. Does it turn on? Light up?
Quote:
So I guess something inside can be changed and replaced right?
Yeah, "something"!! That really narrows it down.

You remind me of myself when my car breaks down and I open the hood and look into the engine compartment. As if I am going to "see" some loose wire or hose, stick it back where it belongs, and be on my merry way. Has not happened yet, but I still open the hood.

You could ask for a miracle: I would open your keyboard up and see if you can see a fuse in there somewhere. There may not even be one, but if there is, remove it, take it to an electronics store and replace it with a fuse of the same value. If that does not fix your keyboard, that means the fuse failed to "catch" the surge and there is more damage "further in" the device. How much and where?

At that point, you are probably going to have to bring it to a qualified technician. Judging from the kinds of questions you are asking, you may not have the skills to do this yourself.

Quote:
I just want to know the name of that piece to find a replacement on a local store or maybe on ebay.
But what people are trying to explain to you is that it might not be a "piece". It could be a fuse, but the power supply - which one would assume would take the brunt of the impact when treated to the wrong electrical connection - is a whole "section" of the guts of your keyboard. It may not conveniently "pop" out, like battery or a fuse. Furthermore, if the surge was powerful enough, it may have gotten "deeper" into the machine, past the power supply, and damaged some of the sound generating circuitry. Only someone who actually knows what he is doing can tell you for sure.

He might first have to fix the power supply before he could even TEST to see if the rest of the unit is OK! At that point you might be throwing good money after bad.

Plus, as TSM said, a discontinued keyboard is not going to have a ton of places that sell "parts" for it. Maybe none. It would be hard enough to get a part for a 1997 automobile, that they made millions of. If you needed a crankshaft from a 1997 Chevy, you would probably have to go to a junkyard. If you are going to buy an old one for "parts", you might as well spend a little more and buy a old one that works.

I took a look around on eBay and Reverb and saw some of these going for a few hundred bucks. Considering that most repair guys charge $50-100 per hour for their time, plus lord only knows what parts, that's the route I would go. Heck while you are at it, you might look around and find something newer, with better sounds and a keyboard action you like better.
Old 8th October 2018 | Show parent
  #18
Lives for gear
 
Wyllys's Avatar
 
๐ŸŽง 5 years
Quote:
Originally Posted by shank91 โžก๏ธ
Hi folks,
I am new here, really need some help with this issue please. The thing is I am getting really into music lately and doing some production now that im in my mid 20s ... so I have this nice piano my dad bought me a long time ago when I was a kid and its a TECHNICS SX-PX222. Unfortunately it burnt some time ago because of connection with wrong voltage.

Power source is 120V but was connected into 220v and burnt.

Can it be fixed? someone told me I had to change the card, but I not quite understand. What should I look up? a repair for the "card" on ebay?

just trying to find some help somewhere on the internet about this. appreciate it
Get some butter and jam. It's toast.
Attached Thumbnails
Using the wrong power supply... what can happen?-image.jpg  
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