Hello

I try to repair the SMPS of my benq fp71g monitor - I know is a hold monitor - but it's
still suitable for me and I repair it for hobby too.

Two years ago I replace many electrolitic capacitors. Now, no other capacitor seem swollen.

https://elektrotanya.com/benq_q7t4-fp71g_sm.pdf/download.html

Schematic is identical to this https://manualzz.com/doc/24617979/benq-lcd-q7c4--fp71v---spare-parts-list except for inverter part.

The fault: I try to power on and nothing happen, no green or amber light no display osd...
When I open the monitor I found the main fuse blow up and the power mosfet (2sk3530) in short circuit between drain and source and a resistance of 140 ohm between G and D\S terminal (D and S are in short circuit...)

I replace 2sk3530 and fuse, check R615 (good) and turn on the power (I use a light bulb in series to AC plug).

Now the SMPS try to start, I see light bulb flashing, backlight stay on for 0.5s or less: I see the OSD but after tihs the monitor turn off, no amber light. If I retry to power on it retry to start again, light bulb flashing, backlight stay on for 0.5 - 1 s.....

I try to unsolder T601 pin 10 (V-inverter) but nothing change.

5V are present and also 3.3V

I can notice a fluctuation of 5V when the light bulb flashing with and without the pin 10 soldered. I should try to disconnect inverter and "replace it" with a dummy load? what kind of dummy load? Resistor? light bulb automotive?

Could be PC123 or TL431 damaged? or in the worst case T061?

Regards

 

Today I try some stuffs.
Fist of all: I test optocoupler pc123 and it's ok. Next I try measure the ripple between terminals of main capacitance. I found a ripple about 160V with and without light bulb in series of AC power. If I try to power on without the light bulb in seriea AC power I can hear T601 "twitting" and I can see ringing artifacts.

My question is: these could be a symtomps of a damage on primary side of T601 or it could be simply C605 in fault?
D601 seems ok

 

Day three. GOOD NEWS!

when I have the power PCB upside down I see a spark from capacitor of RC snubber. As a result I replace the related capacitor and the monitor power up correctly. Unfortunately I don't have the capacitor (I must buy it) so I use a capacitor of identical PCB. Unfortunately T601 still twitting but it could be normal?

Anyway, these are the capacitors. They looks like tantalium cap but they don't have any polarization indication. I suppose they are ceramic type cap.

It seems a good idea replace all 4 caps. On the body I can read:
U2 15J 3kV and 5D 3KV

Can someone tell me the carachteristics of these cap? I suppose 3kV means 3 kVolt...