HK Products Power supply model SPS-200MA

[VK7PD]

Does anyone else have one of these supplies? Mine performed well until it refused to start. It should be repairable but I need a circuit diagram (schematic). The manufacturer won't answer my emails and the retailer (409 Shop) wasn't interested in chasing it up. Any ideas? Peter

[VK4ADC]

A lot of the Asian-sourced power supplies are 'badge engineered' and just because yours has a HK Products label doesn't mean much.  As far as finding a schematic is concerned, well good luck with that task.  Unless it is also marketed under a well-known brand name (eg Manson) then the chances are slim.

I found the following... http://www.dehco.org/WebDocs/Tristar/Wel...Manual.pdf and it is being marketed under the Weltronics brand name, probably others too.   Note that it has a 13.8V 15A rating but is marketed for use in spas & hot tub applications and not for powering radios. Maybe it is similar, maybe not.

These types of supplies fail occasionally, often due to the SMPS main power switch devices punching through and sometimes things like electrolytics failing.  May be as simple as a fuse failing.  Could be an easy fix, maybe.

[VK7PD]

Thanks for the reply Doug. Power gets as far as the first filter C - about 340 volts and produces an output of about of about 3 volts instead of 13.8. It had been doing that for sometime then coming good after a minute or 2. I still suspect and electro drying out. If they were easier to get at, which they are not, I'd borrow an ESR meter and measure them all. There are not that many. I might have to dive into it further and do something like that.
73,
Peter

[VK4ADC]

Peter

The first step is a visual examination of the electros from the top side of the PCB. Check for any that have 'peaked' metal tops instead of flat tops.  Secondly, look at the PCB around the electros' bases and see if there has been any 'gunk' (technical term for discharged electrolyte, often brown or black in colour) released from one or more of them.  If either is true then it will be worth the effort in prying the PCB loose from the case to replace them.

Don't ignore the smaller electros around the PWM controller part of the PCB either. The bigger output ones may be ok but smaller ones (eg 4.7uF..) could be unexpected causes.

The SMPS supplies are a pain to troubleshoot but since you have the 340V DC present, that makes the PWM controller part the most likely culprit. If it isn't the output filter area electros bad (& you already know that the switching transistors/FETs are OK because you get the 3V out of the supply itself), it will probably be part of the output sensing back into the PWM's control input or the supply to the PWM chip.

Do-able.

[VK7PD]

Sorted this one today. It turned out to be a dry joint on a 10UFD 50v electro identified as C17. This C appears to only be used to kick start the SMPS. After it starts it's not used until the next switch on. That made it harder to find as an intermittent. The hardest part was gaining access to the PCB underside due to board mounted power transistors attached to the heatsink. As a supply it performs well but not very accessible to work on. A schematic would have helped localise the fault.