Optiquest/viewsonic q9b flashing power led

[Mr Bill]

I've been going over this monitor for about a week now and i'm stumped. When you press the power button on the monitor the green led lights up, goes out after a second then repeats. The monitor cannot be turned off unless i pull the power cord from the wall. You can hear a brief buzz from the main tranformer then the monitor goes into repeat mode. I am assuming its detecting a fault and is going into some type of protection mode.

The capacitors are rubycon YXG series. I pulled every cap and tested them with my Peak meter and all of them are within tolerance as per rubycons datasheet.

The Pwm controller is SG6841SZ. I checked pin 1 (ground) to all other pins and i am not getting a reading that indicates a short.

On the back side of the power supply there are 4 C5706 transistors that i put a red box around. 2 of them read in circuit shorted. I replaced the 2 and i am still getting the same results. I rechecked the 2 i just replaced after trying the monitor out and in circuit the new ones are reading shorted. I have not pulled them off the board to verify they are shorted yet.

The one thing i find very odd is on the back of the power supply there looks like a jumper wire was added from one a transistor to one pin of the inverter transformer. It almost appears that this was done from the factory, the soldering is very neat and clean.

I am hoping someone has encountered the same issue with this particular monitor. All the info i have found yet points to bloated bad caps which mine has are good

[selldoor]

The one thing i find very odd is on the back of the power supply there looks like a jumper wire was added from one a transistor to one pin of the inverter transformer. It almost appears that this was done from the factory, the soldering is very neat and clean.

Unlikely but worth checking ,is the wire just soldered to the transistor or is it soldered to the resistor as well. If not has the insulation got hot and shrunk allowing it to touch?

[jetadm123]

I suggest you resolder all the pins on T2 and T3. Also, look for bad solder joints and check the values of the two small orange caps marked "H224J" at the bottom of your first photo.

[selldoor]

And if you are getting desperate clean of some of the white glue in case it is going conductive. It is usually brown glue that does that but who knows.

Also can you check the area in the red elipse on the attached to see if it is solder/shorted?

[Mr Bill]

Its soldered to resistor too. I did find a service manual for this monitor but the power board schematic is not included

I follwed the flow chart for no display and you get to a point where it says flashing led check I/F board (main). All the voltage regulators check out and the lelon caps are within spec. I did notice that my 12v is over 13 so that may be what is causing the protection.

From the 30+ monitors i have repaired to date i have never seen a jump wire unless i put it there from boogering up one of the ringlets and didn't have any room to scrape the board to expose the copper. I think with this board i am experiencing sloppy seconds

[retiredcaps]

Originally Posted by Mr Bill

From the 30+ monitors i have repaired to date i have never seen a jump wire

I lost count of the monitors, but I have never seen a jumper wire either. It doesn't mean it can't happen, but I have to wonder.

Were there obvious signs of the lcd being taken apart? I recently fixed a monitor which is now my "main" monitor and it was obviously taken apart. The snaps came apart too easily and I could see fingerprints on certain parts. Luckily, the previous owner didn't butcher anything.

In fact, I got his old "broken" computer with this lcd. 5 years ago, this system cost over $1,000 at Costco. I'm working on the old computer and it will become my "main" computer as well once I'm done. It is easily 2x faster than my dual core setup.

[selldoor]

Yes it is neat soldering but the U10 looks a bit scorched - is it still functioning?
There is also a wire link on the other transformer but as its not isolated doesnt
hit the eye.
Did you check out the " short" in the red circle?