Viotech NB32C Monitor repair

[Tim88]

Greetings, picked up a non-working Viotek monitor. Does not power on, no standby light. Only 2 boards, power and video, video board is good as I piped 12V to it and standby light comes on and get 5v at the test point. Power board only has 12v out and led power. With video board disconnected, I get a variable 12v pin reading of 10.4 to about 11.6 volts. Plug in the video board and the 12v goes way down to around 3v. Cannot find any shorts on the power board. I suspect that the PF6003 PWM controller is faulty but I don't have a differential probe to test it. Am not by any means an expert, in fact, my first time diving into a SMPS. I ordered some 6003's from the ebay from the China from a seller I bought from before but who knows if they will be good. I did find a possible sub in a Onsemi NCP1256, has the same pinout, but above my paygrade on assessing compatibility. I made a schematic from tracing the board, helps me to learn the circuit and attached a copy.

So, any input would be appreciated especially with PWM controller failures such as do they usually short or just flake out. Thanks!

[Tim88]

I removed and tested the zener, tested 23.9 volts. Did another search and it is indeed a 24v zener and not 18v. Voltage across the diode bounced around between 10 and 16 volts before I removed it. Replaced the small electrolytics and the two on the 12v rail, still not regulating. Also tested the startup resistors, all of which were good. Gotta be that IC??? 

[Tim88]

Removed and tested the optocoupler and the MOSFET, both are bueno. Ordered a couple NCP 1256 (A,B & E versions) to try as drop in replacements as the 6003's won't get here till mid Feb...

[Tim88]

Finally got the PWM IC's from the China and we have life! The video board makes a funny squeal when booting up and image has distortion lines. Hoping that is bad caps?

[Tim88]

Replaced the rest of the electrolytics, still buggered. I think I traced the problem down to the video board on the bottom when the ribbon cables go out to the screen. There is 12V fed to that board from the main board, during the boot up it pulls that voltage down and the boot stops. I fed 12V directly to it and has a high current draw and two IC's heat up. You can hear a sizzle/crackle coming from that board like something is shorting. On the 8 pin IV, pins 2, 4 and 6 appear shorted together. Google search for what this one is (marked i2811) and the other big IC (marked RT6820) comes up craps and no data sheet. The i2811 is not the EMF IC that google says, that one is a SOIC and this one is smaller. Any help identifying these IC's would be greatly appreciated especially the 8 pin.

[Tim88]

 I did find this: "MaxLinear (formerly Exar) iML2811 voltage reference buffer" I think it is a IML2811CC part#, anyone have a Maxlinear datasheet catalog?

[Tim88]

I removed the iML2811 IC  and "son of a gun", the short is gone! I found some IC's on Aliexpress, the printing on them looks identical to the original so hope this is an authentic IC. Will let ya'll know how it goes when they get here in a month or so...