Problem with Sony tuner memory

[Lourens]

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!

Thanks
Lourens

 

[Miniwatt]

I GUESS the back-up battery is dead, but I know next to nothing about tuners.

 

[Elso Kwak]

Hi, It is ususally the large capacity backup electrolytic and/or the diode in the supply line to it.

 

[Lourens]

Thank you for your replies.

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

Elso,
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

groeten
Lourens

 

[karma]

if it has a display in the front. it would be a small flat round blue or green cap on the back of the pcb or under the display. this cap would be not to far from the display chip .

 

[DigitalJunkie]

"plus a much bigger Elna 5,5V/0,1uF (hxw=6x12 mm)."

Are you sure that larger cap isn't 5.5V 0.1F(arad)?
That sounds kinda like a memory back-up cap to me.

 

[Lourens]

You're right... it's 0,1 Farad! Sorry...
It is located near the display and uP, on the 'Control' pcb.
It definitely looks very different from all the other lytics, but optically in good condition.
Any hints to make sure it's broken? Or should I just replace it?

 

[Elso Kwak]

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 www.conrad.nl has them.

 

[Lourens]

OK, i'll do that. Thanks Elso, and all others for your kind advise!

groeten
Lourens