My latest project is a Sony SDM-HS93, 19" LCD monitor with CCFL backlights. The person who gave it to me said the monitor would "flash." Before I even turned it on, I opened it up (which was pretty easy since Sony used screws on this monitor instead of the plastic clips which can be a pain to open).
The monitor has the standard layout with the power/inverter board on the left and the video board on the right. There were no bulding capacitors, however one of the caps (C112) had leaked electrolyte out the top, down the side and onto the PCB (see picture). Given this I decided to replace all the caps on the power/inverter board except the big fat one. At the same time, there was a single cap (C840) on the video board with a slightly high ESR. It wasn't really high (.3 versus .03 for the replacement cap), but I decided to replace it as well.
After replacing all the caps I powered on the monitor only to discover that it was still flashing. The flashing is slow and random. The monitor will stay on for 1 - 3 seconds, then stay off for 1-3 seconds. It continues this pattern over and over.
There is a single cable between the power/inverter and the video boards (labeled CN5). The 11 wires are labeled as such:
1. 12V
2. 12V
3. Ground
4. Ground
5. 5V
6. 5V
7. Ground
8. 5V
9. On/Off
10. Dimming
11. Dimming
I've noticed when the monitor is flashing that wire 9 (on/off) switches from 0 to 5V. So my theory is the power/inverter board is functioning properly and the video board is telling the power/inverter board to turn on and off. To test my theory I jumped the 5V standby to the on/off pin. When I did this the backlights came on and stayed on. So I'm pretty sure the problem is on the video board. But I'm not sure what to check next. Any suggestions? Thanks.
The monitor has the standard layout with the power/inverter board on the left and the video board on the right. There were no bulding capacitors, however one of the caps (C112) had leaked electrolyte out the top, down the side and onto the PCB (see picture). Given this I decided to replace all the caps on the power/inverter board except the big fat one. At the same time, there was a single cap (C840) on the video board with a slightly high ESR. It wasn't really high (.3 versus .03 for the replacement cap), but I decided to replace it as well.
After replacing all the caps I powered on the monitor only to discover that it was still flashing. The flashing is slow and random. The monitor will stay on for 1 - 3 seconds, then stay off for 1-3 seconds. It continues this pattern over and over.
There is a single cable between the power/inverter and the video boards (labeled CN5). The 11 wires are labeled as such:
1. 12V
2. 12V
3. Ground
4. Ground
5. 5V
6. 5V
7. Ground
8. 5V
9. On/Off
10. Dimming
11. Dimming
I've noticed when the monitor is flashing that wire 9 (on/off) switches from 0 to 5V. So my theory is the power/inverter board is functioning properly and the video board is telling the power/inverter board to turn on and off. To test my theory I jumped the 5V standby to the on/off pin. When I did this the backlights came on and stayed on. So I'm pretty sure the problem is on the video board. But I'm not sure what to check next. Any suggestions? Thanks.
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