Samsung 940MW power supply problem

[Aleks]

Hello all,

I have an Samsung 940MW which had this problem : for some time it worked and then suddenly it powered off.

I traced the problem to the PSU unit which had leaky and bad output caps.

I changed all of them with the correct values except two which were in parallel and they added up with a total value of 1640 uF/25V (two * 820uF/25V). In their place I put two caps with the values : 1000uF/30V and one with 680 uF/25V.

The problem now is, when I plug the power cord, the green status led turns on for about 2 seconds and then goes off and I can't switch on the monitor.

I've measured the output from the PSU power line which goes to the monitors control board and has the following markings :

BL_EN, BL_CTL, 5V, 5V, GND, GND, GND, 13V, 13V

between GND and the 5V connectors I have 5V output and between GND and the 13V connectors I have 13V. Between GND and BL_EN or GND - BL_CTL I have 0 volts.

What might be the problem ? Is the fact that the value of the two parallel caps is different (40uF difference) causing the PSU to malfunction ?

Regards,
Aleks

 

[Nigel Goodwin]

Usually Samsung TV's corrupt the EEPROM when the PSU caps die, and you have to replace or reprogram them. In the worse cases it damages something on the main board, many of which are no longer available.

 

[Aleks]

Hm.. That would be bad , how can I see of the EEPROM's are bad ? Should I put them on a EEPROM programmer, and would the EEPROM .hex be available somewhere so (if needed) I could reprogram them.

Any other ideas to what might be going on?

Regards,
Aleks

 

[Nigel Goodwin]

Hm.. That would be bad , how can I see of the EEPROM's are bad ? Should I put them on a EEPROM programmer, and would the EEPROM .hex be available somewhere so (if needed) I could reprogram them.

On the TV's often fitting a new blank EEPROM will cause the set to reload it from ROM with rough defaults to get it going, but sometimes you need to obtain an already programmed EEPROM as a spare part.