Hi, I have a Maplin N93CX (aka Manson NRP-2050) variable output SMPS that isn’t working. It’s designed to deliver 0-20v at 0-5A, i.e. 100W total.
I acquired it broken, hence the history isn’t known, but it’s in good condition inside and out. Symptoms were that it comes on, but no output.
Initial tests showed that R62 (0.05ohm 5W) near the +ve output was open, hence I’ve replaced that.
I now get output, but it’s severely limited, going into Constant Current mode almost immediately. Example being a 12v 5w bulb – with the settings at 12v and current max, it goes into CC mode with output of 5v at 0.2A. This is similar for other loads – while the voltage / current vary, it’s always delivering in the region of 1W.
Voltage – I can set it through the entire range (0-20v) and output appears accurate.
There is a preset current limiter, which when I attempt to set it (terminals shorted with voltage set to 3v) I can get to about 1.27A on the display before it stops going up. So that’s 1.27A at 0.1v displayed, i.e. again around 1W or so of output.
I’ve checked numerous components (resistors, capacitors, diodes etc.) throughout the circuit, but struggling to locate anything amiss.
I’m also not familiar with which element of a SMPS controls the output limit (something related to the feedback loop?). Not sure if the fault lies in the current sensing area, or if the supply just isn’t able to provide the output demanded.
Service Manual available here....
https://files.elv.com/Assets/Produkte/7/719/71969/Downloads/71969_nrp2050_data.pdfAny thoughts much appreciated.
Thanks, Paul.