Hi all,
I have a problem with a projector, after a long time without using it, I powered it and it worked for a few hours then two big bangs happened.
I opened the unit and find a current surge limiter burnt and the ballast board with 2 mosfets in short circuit. So I replaced the broken parts and replaced also the electrolytic capacitors.
The power supply board is divided into 3 sections, one produces the 5V standby voltage, the second section produces the 12V for the "logic" board and the last section generates a 385V with a PFC boost circuit for the lamp.
Connecting to the mains the board alone without any other connection, I see the 5V standby power but the 12V for the main board and the 385V for the lamp are "intermittent".
The 12V circuit and the PFC boost circuit are powered up by the same "auxiliary power" circuit, if I remove the PFC chip the 12V works properly but as I assemble again the PFC chip the 12V again starts to work intermittently.
I try lower the lamp output voltage just to understand if the PFC chip is working properly regulating the output and seems to work at lower voltages (I replaced the feedback resistor network to obtain 335V) so in this configuration, I obtained a stable 12V and 335V.
At the moment I'm focusing on the auxiliary circuit which has a periodic charge/discharge capacitor behavior, I understand that there's something that absorbs too much, so to check if there's a faulty capacitor on the auxiliary I added a capacitor but nothing changed. The power supply has also a safe overvoltage circuit that "kills" the auxiliary supply if the lamp voltage goes higher than about 450V. I also removed that circuit but the behavior doesn't change so that part is not faulty.
Any advice? I'm unable to find schematics and I'm running out of ideas.
Thanks in advance for any hints.
Regards