Help with old TV - KDL40XBR6 and time no longer sticking

[tbuccelli]

This is an older television and I have not been able to find information through searching or the manuals.

The TV no longer keeps the time when turned off. Every time I turn it back on, I get the message that time has been lost due to power interruption, or something similar. This message stays on the screen for a minute or two. The TV is not getting unplugged, just turned off.

Is there some internal battery / capacitor that can be replaced? I did replace the power supply board about 5 years ago, and have done a bit of soldering in the past, so I am not concerned about that - I just try to avoid the areas that say "high voltage" on the schematics.

Hoping it is something as simple as a battery, though thinking probably not.

[kgallen]

As you say you’re capable, probably the best you can do is to open her up and look for a coin cell or soldered lithium battery (maybe a Panasonic ML2020 or similar) on the main board. If there is an RTC chip with integrated battery (like the old Dallas 1287) then you might be a bit more stuck. 

[sfbp]

Have you got the service manual? one here at

https://elektrotanya.com/sony_kdl-40xbr6_46xbr6_52xbr6_chassis_ex1_rev.3_sm.pdf/download.html

Looking briefly at it, I don't see a nickel-sized (20mm) battery anywhere. Quite a fancy machine for 2008, one of the only ones with all the connectors before they started taking them away.

[kgallen]

With the SM that Stephen links above...

The RTC (real-time clock) chip is IC3503 (S-35390A) on p34 lower-centre right.

This chip is powered from STBY3.3V which is provided by the switching power supply p54 bottom centre (STBY_3.3V).

If you can understand the schematics in the document then you should be able to fault find from there - check the VDD (pin 8) to VSS (pin 4) on that 8-pin chip. If you have a high impedance 'scope then XOUT on pin 2 should look like a clock (probably a sinusoid) of 32.768kHz (however the load of your scope might quench the oscillations). The chip does not have an internal battery, so the STBY3.3V rail must be used for retention too. As yet, I've not located the cell/battery/cap that supports that rail to maintain the time. Looking around the schematics, there are a fair few chips that hang off the STBY3.3V rail so the tiny 0.25uA retention supply of IC3503 could be swamped by the leakage of the other devices. So I'd expect to find some secondary supply better than a small electrolytic, i.e. like a lithium cell or similar, a super-cap at the least. Still hunting...