[Michael Black[_2_]]

On Sat, 29 Mar 2014, Trevor Wilson wrote:

On 29/03/2014 10:32 AM, Trevor Wilson wrote:
On 13/02/2014 7:57 PM, Sainthunter wrote:
I recently bought a Denon 'Personal Component System/AM-FM Stereo
Receiver DRA-F100' unit from a charity shop - sold for spares or repair.
Apart from a tuner issue the main fault is that after a while in standby
mode it switches off completely from standby as though the mains has
been switched off/a power cut.
Is there a back-up memory battery somewhere, I have tried leaving the
unit powered up and switched on for at least 24 hours kidding myself
that it will recharge the memory battery, if there is one?


**I don't have the service manual for that model, but most machines of
that vintage use a large, low leakage electrolytic cap of approximately
20,000uF @ 6.3Volts. It will likely be near the main microprocessor.



**BTW: By "large", I mean in capacity. The physical size is likely to be
approximately 20 ~ 25mm high and 15mm in diameter.It may also use a
'supercap', which could be in the range of 0.1F ~ 1F @ 5.5 Volts, but I doubt
it.

That's a good point. I remember the cartoons in hobby magazines about
what a Farad capacitor would look like, usually the single unit delivered
ont he back of a truck.

If such large capacitors existed, they sure weren't at the hobby or
consumer level forty years ago. I remember buying a 'computer grade"
electrolytic, the size of a Coke can, 15,000uF at about 16V. Barely high
enough voltage rating for my purposes, but it was what I could get
surplus.

Now you can get even higher capacitance electrolytics in a much smaller
package.

ANd yes, by physical size, you'd never grasp that those backup capacitors
in more recent equipment had such large capacitance values.

Michael