AGT-1783B SMPS

[Donny2derby]

Hi all. The above board is for an LED driver which is causing an issue with the lighting panel strobing/flashing. I found 2 caps bulging that actually tested ok but replaced them anyway.

But now I’m not getting any output at all where I should be getting 48v DC.

On the primary side of the circuit I have found two resistors in series that are each marked 105 so I’m assuming they are 105 ohm resistors and should be getting around 210 when read through them both.

However I get 1.92 Meg Ohm. That is with a capacitor removed which is 0.22 uf but actually reading 97.05 nf out of circuit.

Am I getting somewhere?? Pics of both sides of board attached.

What is the RV1??

Thanks.

[Donny2derby]

Ok this is interesting. Incoming fuse blown (F1) and Diode D1 shorted both ways. Is this common??

[harp]

105 resistor marking is 1000000 ohm, 1 mega ohm, in series with same is 2M.
It is ok, they are in series because to extend gap of high voltage rail (lower voltage drop on each) and serve to discharge capacitor.

RV1 is varistor, for protection.

To see diode markings, use razor blade and with flat blade on surface gently scrap coating over it.
Use angled light, isopropanol, toothpaste and magnificier to see marking.

Check soldering of these components pads:
D6, R6, C7, C9, R9, C11, R19, THT leg near R8 marking.

[Donny2derby]

Ahh that's magic mate. Thanks for your help. I've packed up for the night now but will do as you suggest when I'm back in work later.

Could the two 35 uf 500v caps I found that were blown be as a result of the shorted diode? And would that also explain the blown fuse? Thanks.

[harp]

I dont know whats going on, because initialy you have at least strobe light which mean that fuse was not blown...
From foto, your desoldering skills are good but soldering are suffer. Use flux, rosin... calafonium... pine resin... and practice, practice practice, the solder joint cant be left in condition like this on caps you replace.
Generaly, initialy before soldering on pcb, you do some measurements with include major reading like is input, output, rectifier, caps, mosfets... are ok... and write it. Special measurements do on area which you are plan to work. Write down on paper all readings, then begin with soldering work.
Afret you finish soldering work, you do measurements again, write it on papirus again, and compare results. You do not plug finished pcb simply in mains... it may came to with solder job is somehow do some short, or open, so precaution is always on first place, especialy if you are beginner with lack of experiance. Check, check, check, then test first with bulb current limiter in series...
https://www.badcaps.net/forum/troubl...urrent-limiter

[Donny2derby]

Thank you for the advice. Yes I know my soldering work needs to improve. That’s why I’m working on these SMPS. They don’t belong to me or have cost me any money so they are perfect for enhancing my solder work.

[harp]

Yes, it is good start...
I also suggest, regardles to your intro story, to start collecting free ewaste pcb stuff, so to have random free component near you available in stock.
Also, learn and unerstand how smps work, stages/section, what and how to check, because the most problem is located on power supply board.
Gather or make basic test&work equipment and learn in depth useing it properly.
Next learn your prefered stuff, like tv, how they function, sequences, signals, troubleshooting... say

https://m.youtube.com/@RepairAllTV/videos
https://m.youtube.com/@tevzTVTevatronics/videos

[Donny2derby]

Thanks Harp. The reason for my questions and trying to work on small PCB is to help me learn how SMPS work. I have found a YouTube channel called Haseeb Electronics very useful. If you know of others I will also use them.

i should point out I’m an electrician by trade so have a reasonable under standing of diodes/capacitors/inductors etc. However I’m aware electrics and electronics is very different to learn.

I have certainly learnt a lot from starting. And I'm beginning to understand how to test each component individually. Now I'm hoping to start understanding how they all intergrate.

I have bought lots of test equipment. Component analyser, a good DMM that tests caps/diodes, LED backlight tester, solder rework station, lots of different components to help me test and fix various problems.

Very keen to learn and understand more though and help from people like you is very much appreciated!