Power supply question for pro audio gear - Page 1
Forum section: electronics / repair

author: cfcreative
author_rank: Newbie
timestamp: November 25, 2018, 09:31:13 pm
content: 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 thisCheck whether output current are more than minimum outputcurrent.The output voltage of all channel are stabilized when CH1 (allmodel) and CH2 (only SWT30, 40) are more than minimumoutput currentand for this unit that is .4 amp for the +15v and .2 amp for the +5vso is there a way to test this?Thanks for any responses.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 26, 2018, 01:47:26 am
content: pdf :https://www.mouser.com/datasheet/2/400/tdk-lambda_swt-1207355.pdfIt is a 3 output psu, not 4+5 +15 and - 15 voltsto 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.

author: cfcreative
author_rank: Newbie
timestamp: November 26, 2018, 05:48:42 am
content: I just want to check if it works. Right now when I have it connected to 115v AC I get no output.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 26, 2018, 08:07:32 am
content: they are fused at the input, you should see somekind of fuse ...

author: cfcreative
author_rank: Newbie
timestamp: November 26, 2018, 08:17:52 am
content: 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.

author: PKTKS
author_rank: Super Contributor
timestamp: November 26, 2018, 09:16:28 am
content: Quote from: cfcreative on November 26, 2018, 08:17:52 amActually **ALL** SMPS requires minimum load one way or anotherSMPS are damn oscillators - good only inside the proper windowthe minimum load is there to fulfill that windowOutside the proper window the SMPS will just go wildso it also requires some sort of shutdown procedure outside the proper rangeBTW thanks for the PDF reference...They say "flyback" at fixed frequency but not much about theproper flyback implementation - which makes a hell of a differencePaul

author: coromonadalix
author_rank: Super Contributor
timestamp: November 26, 2018, 11:54:42 am
content: 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.

author: PKTKS
author_rank: Super Contributor
timestamp: November 26, 2018, 01:19:35 pm
content: 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 regulationyou almost certainly will have that "range" for regulationPlease don't insert a uP on the thing - which will change thingson the fly.. Just bare bones SMPS and load regulationSimilar math we do on Linear but it just affects limits of stabilityand poor regulation, may be high freq oscillationWe now have uP controlled SMPS which can change inner passiveparameter (aka reflected impedances) on the flyMuch more complicated and still subject to line regulation issuesSome recent books i've seen devoted chapters to the so calledresonant energy by impedance match... or smps resonatorsThe more you add this issue the better - with no argue as any (hundredsof them) books on SMPS put chapters devoted to minimal loadand regulationPaul

author: commongrounder
author_rank: Frequent Contributor
timestamp: November 26, 2018, 03:17:08 pm
content: 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!

author: Wolfgang
author_rank: Super Contributor
timestamp: November 26, 2018, 04:19:24 pm
content: Pro Audio gear is using switching PSUs ?!?Naah.

author: commongrounder
author_rank: Frequent Contributor
timestamp: November 26, 2018, 05:59:52 pm
content: Quote from: Wolfgang on November 26, 2018, 04:19:24 pmAbsolutely 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.

author: Wolfgang
author_rank: Super Contributor
timestamp: November 26, 2018, 06:32:28 pm
content: what kind of equipment are you referring to ?

author: commongrounder
author_rank: Frequent Contributor
timestamp: November 26, 2018, 07:50:32 pm
content: Quote from: Wolfgang on November 26, 2018, 06:32:28 pmAre you asking about types of equipment, or specific brands and models?Don’t want to veer too far off the OP topic.

author: Wolfgang
author_rank: Super Contributor
timestamp: November 26, 2018, 07:54:29 pm
content: Specific brand and models, please.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 26, 2018, 08:02:33 pm
content: According to the published data sheet:https://product.tdk.com/info/en/documents/spec/swt30_spc.pdfThat model has a MINIMUM load requirement of 200mA @ 5V and 400mA @ 15VI wouldn't attach an unknown (either new or used) power supply to my circuit without testing it first with a dummy load.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 26, 2018, 08:04:23 pm
content: Quote from: Wolfgang on November 26, 2018, 07:54:29 pmWaaay 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.

author: cfcreative
author_rank: Newbie
timestamp: November 26, 2018, 08:05:52 pm
content: Thanks common grounder I will try this. Mouser categorizes it in "switching power supplies"Here is the PDF link for more infohttps://www.mouser.ca/datasheet/2/400/tdk-lambda_swt-1207355.pdf

author: cfcreative
author_rank: Newbie
timestamp: November 26, 2018, 08:08:38 pm
content: 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?

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 26, 2018, 08:16:39 pm
content: Quote from: cfcreative on November 26, 2018, 08:08:38 pmYou 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).