PLP-60-48 Single Output LED Power Supply - "chirping" noise

[CapLeaker]

Nah… that black stuff makes contacts worse, not better. At work I have sometimes trouble with switches because they use cleaner on them.

[stj]

tactile switches are usually silver plated, maybe the black tarnish that builds on them is conductive.

[Agent24]

I am not getting something... first, you had a short on the 2 prongs. You took the Mosfet off, made no diff. Then you took that SMD cap right above the 2 prongs off, now the short is gone on the prongs but the SMD cap isn't shorted? Doesn't make any sense to me.

SMD ceramics are rather delicate, they can be damaged if you solder them wrong and thermally or physically shock them, it's possible to disturb the short internally or crack the capacitor by desoldering it, especially if done with a soldering iron rather than hot air. Then the short would appear to vanish.

I've also had disappearing short circuits on tactile buttons, once the part is desoldered. My guess would be tin whiskers internally on the switch contacts that melted, or similar.

[CapLeaker]

I am not getting something... first, you had a short on the 2 prongs. You took the Mosfet off, made no diff. Then you took that SMD cap right above the 2 prongs off, now the short is gone on the prongs but the SMD cap isn't shorted? Doesn't make any sense to me.

[stj]

Not yet, as I couldn't identify its model and therefore wasn't sure how to test!

the tab is a connection, the first 3 pins are the second connection, the 4th pin is the gate.
check resistance between them all - specially from the tab

[sam_sam_sam]

So it's not abnormal for the whole circuit (with mosfet and cap removed) to show at its input (the prongs) the resistance I specified (1.795 kOhm and if I switch the probes around it - 34 kOhm)?

Might be alright with these readings but with out a working board you will not be sure of it unless you get this board working correctly again then you will know what the actual readings should be

[tester001]

Probably it was shorted before but the heating/movement of desoldering it changed things internally.

So it's not abnormal for the whole circuit (with mosfet and cap removed) to show at its input (the prongs) the resistance I specified (1.795 kOhm and if I switch the probes around it - 34 kOhm)?

[tester001]

did you meter the mosfet out of the board?

Not yet, as I couldn't identify its model and therefore wasn't sure how to test!

[Agent24]

Hi CapLeaker,
Sorry! I've not been very clear. The removed capacitor is showing resistance of 4-5 MOhm and counting. Unable to get capacitance reading..

Resistance of a ceramic cap should be infinite, even in the meg-ohms is not normal. Also not normal if you get no capacitance reading.

Probably it was shorted before but the heating/movement of desoldering it changed things internally.

[stj]

did you meter the mosfet out of the board?

[tester001]

Is that mosfet out too?

Yes, Mosfet has been out (as pictured a few posts above) and the little yello cap that was above the prongs is now out too

[CapLeaker]

Is that mosfet out too?

[tester001]

Hi CapLeaker,
Sorry! I've not been very clear. The removed capacitor is showing resistance of 4-5 MOhm and counting. Unable to get capacitance reading.

The 1.795 kOhm and if I switch the probes around it is 34 kOhm resistance readings are now across the prongs with capacitor removed.

[CapLeaker]

Shorted input capacitor. Check the resistance of that cap and you see it has the weird ohms you measured before between these 2 pins. You can just put a regular electrolytic capacitor in its place (keep the polarity of the cap in mind) like 63v or 100v at 10, 22 or 33uF. This circuit should work without this cap too.

[tester001]

Take that mlcc smd capacitor above the 2 pin prong out and check it out of circuit.

Thank you for your suggestion!

I've taken the capacitor out of the circuit and the meter fails to get a capacitance reading (I gave it time!):


The resistance across the input prongs of the little board with one polarity is now 1.795 kOhm and if I switch the probes around it is 34 kOhm.

Does this mean anything?

[CapLeaker]

Take that mlcc smd capacitor above the 2 pin prong out and check it out of circuit.

[tester001]

To everyone who has been celebrating - Merry Christmas!

With help from colleagues I have desoldered the mosfet from the buck converter board and the resistance across the input terminals is now 159 Ohms.



Should it have increased after de-soldering the mosfet if that component was broken? Just trying to understand the logic behind questining the low resistance across the input terminals being a sign of the problem.

Thank you!

[tester001]

Do you mean adjusting the output voltage on the adjustable power supply I have posted above?

I could, but I usually connect its output to the module that controls the LED - I'm worried that I might damage it if I supply, say, 48 volts instead of 40.

Not sure what to do really. I've ordered this buck converter https://www.aliexpress.com/item/1005004336673431.html but I suspect it would crumble when having to deliver 30 W to the LED, even if I install the heatsink.
There is no room within the case for a larger, more powerful buck converter or an adjustable Mean Well PSU model that outputs 40v.
Whoever designed this device felt that this little board was capable of acting as a reliable buck converter from 48v to 40v at 1.2A, but all models for such spec that I've seen online are much larger and have heatsinks. To make matters worse we can't even identify the mosfet model used - must be some noname chip that is no longer manufactured

[tester001]

EDIT: duplicate post

[sam_sam_sam]

Could be! I replaced the little board with this:

And set the adjustable power supply to output 40V with 1.5A max. The LED device sprung to life!

Did you try adjusting the buck converter to a slight higher voltage than 40 volts I suspect that your current would go up somewhat as well but do not exceed the current rating of the LED light module otherwise you could damage it if pulls to much current
if It bright enough at 40 volts try it at a lower voltage until it gets real dim or LED light bulbs go dark and then increase the voltage until all of the LED lights bulbs are lighting and see what voltage that is then you can determine what is the best voltage to run it at with the least amount of current the LED light module will last longer in the long run