OZ960 Intelligent CCFL Inverter Controller - Circuit Modification - Page 1
Forum section: electronics / repair

author: 2X
author_rank: Frequent Contributor
timestamp: July 10, 2023, 09:32:31 pm
content: Hi, I have a SAMSUNG LCD Pc monitor and it shows for one second the logo and then the screen turns to totally black. The problem is on OZ960 Intelligent CCFL Inverter Controller. I bypassed the protection of the chip as it shown on the below video and works fine but it has no protection anymore. After search on web as I understanded that the problem is the uneven current that the lamps draw and that triggers the protection of the chip (but I am not sure about this because when I leave only one lamp connected it makes the same thing, so can both lamps have obtain a problem simultaneously?). My question is how can I change he current (or voltage) limit little bit in order not to trigger the protection of the chip and from the other hand the chip will continue to have the protection enable? I beleive that I have to change one of the components that they are connected to pins 9 & 10... I made some changes in the values of the resistors R9 & R8 but with no success.

author: asis
author_rank: Frequent Contributor
timestamp: July 11, 2023, 03:50:18 am
content: Hi,Don't do what shouldn't be done.It's easier for you to find an old monitor and dismantle the CCFL lamps or buy them - the appropriate size.Before doing this, find somewhere a high-voltage power supply from an old scanner or MFU and connect it to a laboratory power supply.As a rule, this module operates from +24V DC power supply.The laboratory source will allow you to vary the voltage and control the current at which the CCFL ignites.Before proceeding with the deep disassembly of the matrix, check all the available lamps in this way, this will allow you to reject the lamps in your monitor and in the donor.All this work requires accuracy, since during disassembly / assembly, matrix cables can be damaged.

author: 2X
author_rank: Frequent Contributor
timestamp: July 11, 2023, 04:42:52 am
content: Because the monitor is mine, I would like to experiment with the OZ960 chip in order to learn things. For that and I want the modification that I described.

author: asis
author_rank: Frequent Contributor
timestamp: July 11, 2023, 10:16:19 am
content: Hi,I, just like you, went this way, and realized that CCFLs tend to degrade.And if, as a result of a corona discharge, the current through the lamp does not reach certain values, the inverter goes into protection.Go ahead.

author: 2X
author_rank: Frequent Contributor
timestamp: July 11, 2023, 01:06:55 pm
content: What I have to modify so to give a little tolerance to this "fault". What resistor or what component I have to change in order to continue to have the chip protection enabled?

author: wraper
author_rank: Unknown
timestamp: July 11, 2023, 04:37:52 pm
content: Did you check resistance of transformer secondary windings? Faulty lamp and transformer give the same symptoms.

author: 2X
author_rank: Frequent Contributor
timestamp: July 11, 2023, 06:04:22 pm
content: Hello, as I remember I measured in all windings the same Ohm, but I will recheck them... Could you tell me what is a normal value approximately for a good winding (points A,B,C,D,E,F - at the image below) and what for a faulty winding?

author: wraper
author_rank: Unknown
timestamp: July 11, 2023, 10:49:05 pm
content: Secondary windings usually have around 1k resistance and it must be almost equal for all of them.

author: 2X
author_rank: Frequent Contributor
timestamp: July 12, 2023, 06:18:25 pm
content: Hi again,I measured the windings and the results seems good to me.