Is This a Battery ?

[mmartell]

This is from a Samsung bookshelf system - SCM-6900 circa mid eighties (?) that had burnt lamps in the tuner and cd lcd's - two in each. I replaced those with some mini lamps I had around and was about to put it back together for use in my garage until something better came across my workbench but realized after power outage all presets were wiped.

So of course I'm looking for a dead battery of some kind but this is all I can find. It is next to the tuner lcd but the label on the board indicates capacitor. It actually reads about 0.8v with power removed where other caps are nearer zero.

Ideas ?

[stj]

Re: Is This a Battery ?

that's what your looking for.

it may actually be a storage capacitor.
sometimes called a "gold cap", a "super cap", a "double-insulated cap" among other names.

you need to desolder it and read what's printed on it.

[mmartell]

Re: Is This a Battery ?

Excellent ! Thanks stj, will report back tomorrow.

[R_J]

Re: Is This a Battery ?

here is a link to digikeys list; http://www.digikey.ca/product-search...percaps/131084

[mmartell]

Re: Is This a Battery ?

Thanks for the link. Just pulled this cap, only markings are "Japan 192". Will try to match it up.

Don't suppose this can be substituted by something more readily available ? Truth is I would rather get this dinosaur off my bench lol.

[budm]

Re: Is This a Battery ?

It is used for storing the programmed radio station that you choose, so if you do not need the unit to remember those radio stations, then you will not need it in place, some of my old stereos have 2 AA batteries holder for the back up batteries just for that purpose.

[mmartell]

Re: Is This a Battery ?

There are finer markings than I could see at first. It's a Panasonic 5.5v 0.047F.

Wish mine had the batteries instead, bud, would make for an easier repair since I don't have this on hand. I guess I'll put an order together and fix it right.

[stj]

Re: Is This a Battery ?

batterypack will work if you put it through a diode.

[budm]

Re: Is This a Battery ?

You can try CR3032 Coin cell, the Negative of the battery to the negative pad on the board, the Anode of the Schottky diode (for less Vdrops on the diode) to the positive terminal of the battery, the Cathode of the Diode to the Positive pad on the board.

[mmartell]

Re: Is This a Battery ?

What about two cr3032 through a standard diode ?

[budm]

Re: Is This a Battery ?

I suggest the Schottky because the Vf of Schotty is around 0.20V instead of 0.6~0.7V for regular diode. I hope around 3V will be enough to keep the memory going.
The current draw is very small so small diode will work. I am sure you have Schottky diodes around.
Not sure if 5V will be too high or not.

[budm]

Re: Is This a Battery ?

OK, it runs on 5V so two 3V batteries and diodes (may be 2), you will have to check the Voltage with the unit unplugged, if it is too high it will cause UD10 to be biased off so instead of running from the power supply, it will run from the batteries instead.
SCM-6700 is probably same setup as yours, UC15 in the SCH is the backup cap.

[mmartell]

Re: Is This a Battery ?

...if it is too high it will cause UD10 to be biased off so instead of running from the power supply, it will run from the batteries instead.

Ok this will really show my ignorance but... when the unit is on and the diode UD10 is forward biased what stops UC15 from feeding into the circuit as well ? Is it because the anode of the cap is positively charged ? Does it have anything to do with differing potentials ?

[budm]

Re: Is This a Battery ?

When the unit is on, the diode UD10's Anode is fed with 5.6VDC power supply, the output on the Cathode side then will be 5.6V - 0.6Vf for UD10 = 5VDC to feed the VDD pin of the IC UIC1 pin 73, the back up cap is also charged through the 47 Ohms resistor ( the resistor is for limiting the inrush current due to when cap is first charge will be seen by the circuit as shorts). When the power is remove from the unit, the charge Voltage on the cap is then used for backup.

[stj]

Re: Is This a Battery ?

problem solved,
the ram is retained down to 1.3v

so use a coincell-holder and a 1n4148 diode.

[budm]

Re: Is This a Battery ?

Good news indeed.

[mmartell]

Re: Is This a Battery ?

When the unit is on, the diode UD10's Anode is fed with 5.6VDC power supply, the output on the Cathode side then will be 5.6V - 0.6Vf for UD10 = 5VDC to feed the VDD pin of the IC UIC1 pin 73, the back up cap is also charged through the 47 Ohms resistor ( the resistor is for limiting the inrush current due to when cap is first charge will be seen by the circuit as shorts). When the power is remove from the unit, the charge Voltage on the cap is then used for backup.

Thanks bud but my ignorance goes deeper than that lol. I think what I'm asking is what makes a capacitor "turn on" or discharge ?

Now that I'm thinking about it.. is it the point where the voltage on its anode falls below that of the stored charge within it ?

I can't conceptualize it as the voltage from the diode would "push against" that of the discharging cap as the diode shuts off (because it's not instantaneous). Clearly I am missing something basic.

[mmartell]

Re: Is This a Battery ?

problem solved,
the ram is retained down to 1.3v

so use a coincell-holder and a 1n4148 diode.

Thanks stj. I will double check that I have the same ic as mine is actually a slightly different model.

[mmartell]

Re: Is This a Battery ?

This uses a different ic and even the 2+ volts I was pushing wasn't enough to keep the memory alive. Ran out of time will try tomorrow with closer to 5v.

[stj]

Re: Is This a Battery ?

so what is the ic number?