Power supply question for pro audio gear

[cfcreative]

Hello. I have an ebay purchase of an audio processor that I am trying to trouble shoot.

The power supply that is used in this unit is called a Nemic Lambda swt30-5ff. I looked up the spec sheet and it says that it can take 115 to 20v in and then output +15, -15, +5,+5 and ground but I am getting nothing.

In the troubleshooting section I read this

Check whether output current are more than minimum output
current.
The output voltage of all channel are stabilized when CH1 (all
model) and CH2 (only SWT30, 40) are more than minimum
output current

and for this unit that is .4 amp for the +15v and .2 amp for the +5v

so is there a way to test this?

Thanks for any responses.

[coromonadalix]

pdf : https://www.mouser.com/datasheet/2/400/tdk-lambda_swt-1207355.pdf

It is a 3 output psu, not 4  +5 +15 and - 15 volts

to test the maximum output you could do :  5v at 2 amps is 2.5 ohm load, if you put an 2 ohms load  it should go in overload,  15v at 1 amp is 15 ohms  etc ....  but they have an higher peak current,  you must have the loads slightly lower than the peak values current to trigger an overload or an shutdown if its equiped that way.

[cfcreative]

I just want to check if it works. Right now when I have it connected to 115v AC I get no output.

[coromonadalix]

they are fused at the input,  you should see somekind of fuse ...

[cfcreative]

If you read the original post it says that there has to be a small load on the power supply can anyone explain this to me.

[PKTKS]

If you read the original post it says that there has to be a small load on the power supply can anyone explain this to me.

Actually **ALL** SMPS requires  minimum load one way or another

SMPS are damn oscillators - good only inside the proper window
the minimum load is there to fulfill that window

Outside the proper window the SMPS will just go wild
so it also requires some sort of shutdown procedure outside the proper range

BTW thanks for the PDF reference...

They say "flyback" at fixed frequency but not much about the
proper flyback implementation - which makes a hell of a difference

Paul

[coromonadalix]

I wont argue with PKTKS, but our open frames and closed frame psu(s) like the OP  have somekind of load or an bleeder resistor to empty the output capacitors on the board itself, you can power them and test them without any load on the output, ad they are stable and rock steady.

We have many of them, Condor and Meanwell mostly, from 5vdc up to 54 volts,  none of them needs a load to start, only one of them have a remote power on, if we enable it with an jumper. ? 

I ve seen tons of smps, they dont always need a load to sart and run ... the only ones i know know to do that are the computers and servers power supply (ies)
 
You have many topologies  to implement an smps, buck boost, fixed or variable frequency (ies)   etc ....  it depend on the design you need or use  i may say.

Edit : i have at home, Corsair and Thermaltake psu, they start without the mobo or any hard drive on them,  just need to short the power signal on the 24 pins plug.

[PKTKS]

No no no nothing to argue.. not even disagree.

In fact no SMPS requires the load to start or function..

the matter is REGULATION.

When you do the math on inductors caps and MIN/MAX load regulation
you almost certainly will have that "range" for regulation

Please don't insert a uP on the thing - which will  change things
on the fly..   Just bare bones SMPS and load regulation

Similar math we do on Linear but it just affects limits of stability
and poor regulation, may be high freq oscillation


We now have uP controlled SMPS which can change inner passive
parameter (aka  reflected impedances) on the fly

Much more complicated and still subject to line regulation issues

Some recent books i've seen devoted chapters to the so called
resonant energy  by impedance match... or smps resonators

The more you add this issue the better - with no argue as any (hundreds
of them) books on SMPS put chapters devoted to minimal load
and regulation

Paul

[commongrounder]

Based on the info the OP supplied, I would disconnect the preamp circuitry from the power supply, and attach a 22-ohm 1 watt (or larger) resistor across the +5 volt supply, and a 33-ohm 10 watt resistor across the +15 volt supply.  If it is working normally, it should power up and stabilize to the nominal voltages on each rail. If it doesn’t, check the caps (the new rallying cry of servicers everywhere!). There is also a possibility of a problem with the pre-amp circuitry dragging down one of the rails, so divide and conquer!

[Wolfgang]

Pro Audio gear is using switching PSUs ?!?
Naah.

[commongrounder]

Pro Audio gear is using switching PSUs ?!?
Naah.

Absolutely yes!  I see it all the time.  It’s even more common now that digital power amplifiers are available. Efficiency and light weight are big selling points.
Seriously, though, it is quite normal to see high quality switchers used in high-end consumer audio equipment, as well as the professional stuff.

[Wolfgang]

what kind of equipment are you referring to ?

[commongrounder]

what kind of equipment are you referring to ?

Are you asking about types of equipment, or specific brands and models?
Don’t want to veer too far off the OP topic.

[Wolfgang]

Specific brand and models, please.

[Richard Crowley]

According to the published data sheet:  https://product.tdk.com/info/en/documents/spec/swt30_spc.pdf

That model has a MINIMUM load requirement of 200mA @ 5V and 400mA @ 15V

I wouldn't attach an unknown (either new or used) power supply to my circuit without testing it first with a dummy load.

[Richard Crowley]

Specific brand and models, please.

Waaay too many to enumerate.
Even highest-end ultra-pro analog audio gear is found with SMPS. 
People stopped complaining about that years ago.
Nothing wrong with SMPS when the system is designed properly.

[cfcreative]

Thanks common grounder I will try this. Mouser categorizes it in "switching power supplies"

Here is the PDF link for more info https://www.mouser.ca/datasheet/2/400/tdk-lambda_swt-1207355.pdf

[cfcreative]

So where the power supply connects to the board I can put a meter across from the 15v connector and to ground and I can see what load it is to see if the fault is on that side?

[Richard Crowley]

So where the power supply connects to the board I can put a meter across from the 15v connector and to ground and I can see what load it is to see if the fault is on that side?

You can measure the VOLTAGE output from each of the three outputs relative to ground by probing with your meter in voltage mode. That appears to be what you are already doing.

If you want to measure CURRENT on each of the outputs (one at a time unless you have three meters) you must put the meter (and the test leads) into CURRENT mode and connect the meter in SERIES between the power supply and the load (replacing the wire).