Hello to everyone,
I recently bought a used display – Samsung Syncmaster T190. When I brought it home and plugged it into my computer, I found out it's completely dead:
-No backlight
-No image
-No power indicator LED glowing
-No reaction from the touch sensor button or any button at all.
So I decided to try repairing it. I have repaired a few LCD screens in the past and a few SMPS by recapping them, so I thought “why not”?
I took off the power supply board and examined it. There were two bumpy leaky capacitors visible. I took them off, measured their ESR, it was 1.1R and 1.8R.
I decided to replace all capacitors, even those on the processor board. I used Fujicons low ESR series 105C, except on a place where 3 caps where in parallel. Because I had much higher voltage Fujicons for there and they couldn't fit. I decided to solder 3 no-name brand ones.
When I plugged everything like it was and turned the power on again – nothing happened. It was dead again, the same way it was before, when I bought it.
Then I measured the voltages coming from the power supply board to the processor board:
- 15,8V measured on the +14VDC rail
- 5,2V measured on the +5VDC rail
I also examined the processor board and its datasheet. The processor's name is SE758MRH-LF.It turned out, it has three local regulators: 1,8V ; 3,3V ; 3,3V. They are feeded from the +5VDC rail. It turns out, the first local regs 1,8V and 3,3V are feeded only when a mosfet switch saturates when its GATE connected to KEY1 pin goes to positive 3,3V
I tried measuring all the local regs with the KEY1 pin to 3.3V and the voltages are good. But I also found out, that the power LED never turns. I even soldered a local LED near the Vled out pin, but I had no result.
On the power board, there is a ON/OFF pin that when connected to PIN1, turns the backlight on, but no image outputs. Also, the power sensor button works in this situation. I also tried connecting ON/OFF to PIN1 and 3.3V – still only the backlight exists, but I get no image.
So, in summary:
-The voltages measured with a DMM measure okay, except for the 15,8V on the +14VDC rail.
-The power LED doesn't turn on.
-The ribbon cables seem okay.
-The CFL work
-The ON/OFF connected to KEY1 brings the backlights
And I have some things to try before going desperate about it:
-Measure each voltage rail with an oscilloscope
-Change the no-name parallel new caps I put with low esr fujicons.
I recently bought a used display – Samsung Syncmaster T190. When I brought it home and plugged it into my computer, I found out it's completely dead:
-No backlight
-No image
-No power indicator LED glowing
-No reaction from the touch sensor button or any button at all.
So I decided to try repairing it. I have repaired a few LCD screens in the past and a few SMPS by recapping them, so I thought “why not”?
I took off the power supply board and examined it. There were two bumpy leaky capacitors visible. I took them off, measured their ESR, it was 1.1R and 1.8R.
I decided to replace all capacitors, even those on the processor board. I used Fujicons low ESR series 105C, except on a place where 3 caps where in parallel. Because I had much higher voltage Fujicons for there and they couldn't fit. I decided to solder 3 no-name brand ones.
When I plugged everything like it was and turned the power on again – nothing happened. It was dead again, the same way it was before, when I bought it.
Then I measured the voltages coming from the power supply board to the processor board:
- 15,8V measured on the +14VDC rail
- 5,2V measured on the +5VDC rail
I also examined the processor board and its datasheet. The processor's name is SE758MRH-LF.It turned out, it has three local regulators: 1,8V ; 3,3V ; 3,3V. They are feeded from the +5VDC rail. It turns out, the first local regs 1,8V and 3,3V are feeded only when a mosfet switch saturates when its GATE connected to KEY1 pin goes to positive 3,3V
I tried measuring all the local regs with the KEY1 pin to 3.3V and the voltages are good. But I also found out, that the power LED never turns. I even soldered a local LED near the Vled out pin, but I had no result.
On the power board, there is a ON/OFF pin that when connected to PIN1, turns the backlight on, but no image outputs. Also, the power sensor button works in this situation. I also tried connecting ON/OFF to PIN1 and 3.3V – still only the backlight exists, but I get no image.
So, in summary:
-The voltages measured with a DMM measure okay, except for the 15,8V on the +14VDC rail.
-The power LED doesn't turn on.
-The ribbon cables seem okay.
-The CFL work
-The ON/OFF connected to KEY1 brings the backlights
And I have some things to try before going desperate about it:
-Measure each voltage rail with an oscilloscope
-Change the no-name parallel new caps I put with low esr fujicons.
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