Hi guys,
Have a strange one with a Grundig TV I bought from one of the ebay type websites here in Ireland... Guy said that it doesnt power on. So I got it home and took the back off, stuck a hairdryer across the secondary section of the PSU and it powers on... So I'm thinking, grand it's the electrolytics. However I pulled every one of them off the PSU and they test fine.
So, even though I know that heating the secondary section of the 17IPS02-2 PSU brings the power on, I decided to trace the startup signal from the video board. There is a KA78R12 voltage regulator, which is switched on and off by the voltage present at PIN 4.
STANDBY: When the TV is in standby, there is 1.63v present at the STBY_ON/OFF, Q806 is turned on, PIN4 of the KA78R12 chip is low (and turned off).
TV ON: After heating the secondary section, the TV eventually powers on. When the TV is on there is 0V at STBY_ON/OFF, Q806 is turned off meaning that PIN4 of KA78R12 is high (and turned on powering the video board).
BUT, when the TV is in the state that you are pressing the button but it is not powering on, there is no voltage change on the STBY_ON/OFF. this would make me think that there is a problem with the signal coming from the video board... (which would contradict the fact that the TV definitely powers on when I heat the secondary section of the PSU)
I want to force the power on... If plug out the video board connection and just jumper BL_ON and STBY_ON/OFF to ground (using a 100ohm resistor), will this do the job? I know that the AD/DIM is for controlling the amount of current to the backlight, but what is the SOFT_SWITCH for?
Have a strange one with a Grundig TV I bought from one of the ebay type websites here in Ireland... Guy said that it doesnt power on. So I got it home and took the back off, stuck a hairdryer across the secondary section of the PSU and it powers on... So I'm thinking, grand it's the electrolytics. However I pulled every one of them off the PSU and they test fine.
So, even though I know that heating the secondary section of the 17IPS02-2 PSU brings the power on, I decided to trace the startup signal from the video board. There is a KA78R12 voltage regulator, which is switched on and off by the voltage present at PIN 4.
STANDBY: When the TV is in standby, there is 1.63v present at the STBY_ON/OFF, Q806 is turned on, PIN4 of the KA78R12 chip is low (and turned off).
TV ON: After heating the secondary section, the TV eventually powers on. When the TV is on there is 0V at STBY_ON/OFF, Q806 is turned off meaning that PIN4 of KA78R12 is high (and turned on powering the video board).
BUT, when the TV is in the state that you are pressing the button but it is not powering on, there is no voltage change on the STBY_ON/OFF. this would make me think that there is a problem with the signal coming from the video board... (which would contradict the fact that the TV definitely powers on when I heat the secondary section of the PSU)
I want to force the power on... If plug out the video board connection and just jumper BL_ON and STBY_ON/OFF to ground (using a 100ohm resistor), will this do the job? I know that the AD/DIM is for controlling the amount of current to the backlight, but what is the SOFT_SWITCH for?
