Problem with Sony tuner memory

When I disconnect my old Sony ST-S770ES tuner from the mains for longer than a few minutes, all stored information has gone.
I guess some cap has to be replaced, but I am not sure which one or where to look. On the ‘control board’, near of the printed indication ‘back up’?

I don't have a service manual, so any help is greatly appreciated!

Thank you for your replies.

there is no (detachable) back-up battery like I know them from computer motherboards.

could you be a bit more specific, please: how large is 'large', for instance? There are several 330-470uF 'normal' ones located around the psu, one 'huge' (in my perception :) 63V/2200uF (labeled 'Negative Black') and 2x 'big' 63V/1000uF.
On the control board (near the microprocessor, with RAM i presume?) 2x 'small' 50V Elna's (3,3 and 10uF), plus a much bigger Elna 5,5V/0,1uF (hxw=6x12 mm).

BTW, i tried in vain to detect some standby voltage supplying the suspected back-up electrolytic in off-position, assuming this voltage should be present because as long as the tuner is connected to the mains, he never forgets anything.

Wish i had a digital camera at hand, or a schematic... still hoping this helps to get some more advise:confused:

Hi Lourens, Just replace the cap. Yes it is in Farads not µF. Also replace the diode in the supply line feeding the cap. The diode is for preventing the cap becoming empty into the supply when power is off. Usually the diode gets leaky by the large inrush current when power is applied. Replace by an 1N4004 type regardlkess what Japanese type is used. I replaced many of these caps and diodes as a repair technician.
If you have trouble finding a cap like you need has them.