Test 18v adapter for power

[gsc1ugs@gmail.com]

How do i test a 3 pin adapter that doesn’t have earth with a multimeter, it has pins 1,2,3
Red green white. Im just getting nonsense off multimeter

[gsc1ugs@gmail.com]

Its to power a yamaha mg82cx mixer

[Wonks]

Just because it has a 3-pin plug doesn't mean the ground is carried through to the output. It may well have a virtual ground.

If there's a Class 2 square in square symbol, then it's double insulated and the earth connection won't be carried through to the equipment plug side.



From web images of the Yamaha power supply it is class 2 and it's got a double 18v AC supply. Pins 1 and 3 on the equipment connector are 18v AC and Pin 2 is 0v AC.

So measure AC voltage between pin 2 and 1, and between pin 2 and 3 and you should get 18v AC. If not 18v on both pairs, then you may have a broken wire in the connector. I've had that on an Alesis mixer I bought used, that had an identical connector.

The strain relief on the connector isn't great if the cable used is on the thin side and they haven't added any heat shrink to thicken it up.

[gsc1ugs@gmail.com]

Thanks for replying, so the multimeter black goes to 1 and red goes to pin 2 is that correct? you mention 2 and 3 is that blk to 2 red to 3? Not a genius with this stuff

[ef37a]

https://www.proaudioservice.co.uk/produ ... ac-mg82fx/

That is one of several sources I found very quickly. If it were my mixer I would be putting a nice, chunky 45va toroid in a tin! OP is obviously not up to that.

Dave.

[gsc1ugs@gmail.com]

Just because it has a 3-pin plug doesn't mean the ground is carried through to the output. It may well have a virtual ground.

If there's a Class 2 square in square symbol, then it's double insulated and the earth connection won't be carried through to the equipment plug side.



From web images of the Yamaha power supply it is class 2 and it's got a double 18v AC supply. Pins 1 and 3 on the equipment connector are 18v AC and Pin 2 is 0v AC.

So measure AC voltage between pin 2 and 1, and between pin 2 and 3 and you should get 18v AC. If not 18v on both pairs, then you may have a broken wire in the connector. I've had that on an Alesis mixer I bought used, that had an identical connector.

The strain relief on the connector isn't great if the cable used is on the thin side and they haven't added any heat shrink to thicken it up.

Ive just done reading on 2 and 1 and 2 and 3 and i get 22.57 v readings ?

Its ment be 18v adapter

[Wonks]

That's the voltage without a load. With the mixer connected it will drop close to 18.5v (it's actually 18.5v not 18v) But you can't test that easily without opening up the mixer.

One 18.5v goes to creating a positive DC rail, the other to creating a negative DC rail.

If you measured the AC between pins 1 and 3, you might get almost nothing or you might get over 40v AC. 40v or more would indicate a centre tapped transformer.

[gsc1ugs@gmail.com]

So would you say the adapter is functional?

I do get 45v at 1 and 3

[Wonks]

It would seem to be working as it should if you are measuring 22v AC between pins 2 and 1 and 3 and 1.

Is the mixer lighting up at all?

[gsc1ugs@gmail.com]

It would seem to be working as it should if you are measuring 22v AC between pins 2 and 1 and 3 and 1.

Is the mixer lighting up at all?

No, i think ive been sold a duff unit

[Wonks]

If it's a used mixer, it might be something simple to fix like a cracked solder joint on the power connector. There may be an internal fuse that's gone. But there are multiple other causes which won't be easy to fix.

[gsc1ugs@gmail.com]

If it's a used mixer, it might be something simple to fix like a cracked solder joint on the power connector. There may be an internal fuse that's gone. But there are multiple other causes which won't be easy to fix.

I took it apart and was hoping internal fuse but no, could a capacitor be at fault theres 4

[Wonks]

It could be, but could easily be a power regulator chip or something else.

[Hugh Robjohns]

...so the multimeter black goes to 1 and red goes to pin 2 is that correct? you mention 2 and 3 is that blk to 2 red to 3? Not a genius with this stuff

It's an AC voltage, so it doesn't matter which colour probe goes to which terminal.

The output is a centre-tapped transformer. So from centre (pin2) to either end (pin1 or pin3) should give 18.5V* AC — make sure you set your meter to read AC volts.

If you meter the two ends of the transformer (pin1 and pin3) you should see 37V* AC.

* In practice, the voltages might be a little higher than the nominal rating as there's no load on the transformer.

....but if you've got Volts from the PSU but the mixer is not working — and you have switched it on... — I'd send it back.

If it's doing nothing at all it's a power section failure.

[gsc1ugs@gmail.com]

I get 22.5v ac set off pins 1, 2 and 45v off the other 2,3 will check again, if i did open mixer at which point could i read the 18v?

[ef37a]

If it's a used mixer, it might be something simple to fix like a cracked solder joint on the power connector. There may be an internal fuse that's gone. But there are multiple other causes which won't be easy to fix.

I took it apart and was hoping internal fuse but no, could a capacitor be at fault theres 4

Poor practice not to fuse the incoming AC. Might be some soldered in "Wickman" fuses? They look like small, dumpy capacitors, usually brown.
I guess thought that the designers rely on a one shot heat fuse in the transformer to protect against gross overloads?

Dave.

[gsc1ugs@gmail.com]

Gonna take a pic, those i thought was capacitors is prob the wickmans

[ef37a]

Gonna take a pic, those i thought was capacitors is prob the wickmans

Well, think on chuck! IF the Wickman fuses exist and they have blown you have some deep doo-dah wrong with that mixer so unless it is for your own interest I wouldn't bother?
Wickmans btw are about the size of a fat hearing aid battery.

Dave.

[Wonks]

There are also small rectangular fuses for surface mount soldering roughly about 1cm long and a couple of mm square. Ceramic lookimg body with metal end caps. I had one blow in my Genelecs. They come in all differing sizes so I ordered replacements that came with holders, so if they ever blow again it's easy to replace.

Doesn't necessarily mean there's something wrong with the rest of the circuit, (my Genelecs have been fine since) but there might be.

[ef37a]

There are also small rectangular fuses for surface mount soldering roughly about 1cm long and a couple of mm square. Ceramic lookimg body with metal end caps. I had one blow in my Genelecs. They come in all differing sizes so I ordered replacements that came with holders, so if they ever blow again it's easy to replace.

Doesn't necessarily mean there's something wrong with the rest of the circuit, (my Genelecs have been fine since) but there might be.

I am not familiar with those ceramic fuses. The only circuit I have to hand that uses Wickmans is that of an HT-5. The fuses in each leg to the bridge rect' are 2.5A, way above the rating of the regulators that follow. That tells me that soldered in fuses such as this are intended as a "last ditch fire stop" measure?

Needless to say? I never had one pop in a Five!

Dave.

[Wonks]

More an 'easy to mount with a pick and place machine' measure that doesn't need a human or a separate machine to fit the fuses in a holder.

Also ties in with the 'no user replaceable parts inside' philosophy that is so prevalent with consumer electronics.

[Hugh Robjohns]

The schematics are easily found on line. Here's the power supply section.

The audio circuitry is run on +/-15Vdc, with a 12Vdc supply for LEDs, 5Vdc for the digital stuff and +48Vdc for phantom.

So, if you are keen to fault-find this desk yourself, I'd start by checking for the presence of those voltages at the power supply outputs...

There are no lethal voltages inside the desk, so it is safe to work on, but there is a risk of damaging things if you don't know what you're doing from an electronics point of view.

[gsc1ugs@gmail.com]

I found the problem, regulators and transistors need soldering, broken joints, i then had power, thanks to all you help, mixer must of took a bang

[Hugh Robjohns]

Wow! Good find... but disturbing.

Best check everything else for broken joints too.

[Wonks]