Audio system does not retain tuner memory

[anuragn]

I have a JVC audio system (model UXG38). It looks like the picture attached below.
The problem is that whenever I keep it powered off (i.e. unplugged from mains), it loses the tuner preset memory by the next day. When the system was new, it used to retain the memory for 2-3 days.
I suspect that the associated capacitor has become weak and discharges quicker. Hence I want to replace it, probably with a higher vapacity one but do not know which one to replace. Is it the main power capacitor at the power supply or some other one nearer the memory chip (how to identify?).
Hence I need a service manual or else, if somebody can suggest some other solution (other than keeping it powered all the time :sad

 

[gobble]

Maybe there is a watch type battery somewhere on a pcb that needs replacing?
Don't think they would rely on caps for this...

--G0bble

 

[anuragn]

Maybe there is a watch type battery somewhere on a pcb that needs replacing?
Don't think they would rely on caps for this...

--G0bble

Gobble, I have not yet opened it but I dont expect a battery. Reason: In the user manual it is mentioned that it will lose the memory if kept unplugged for a few hours (but used to last 2-3 days when new).
The issue is that earlier it used to retain for 2-3 days but nowadays it doesnt last more than a few hours. And tuning all 8-9 FM stations everyday is a pain.

 

[venkatcr]

As Gobble say, most systems use an internal battery to retain some data. A capacitor does not hold charge for a long time. 2-3 days is out of the question.

Cheers

 

[wlg]

Hi
I dont think there is a battery or capactor but an EPROM saving the necessary changes when tunning your stations, the only suggestion I have is to keep the set on standby (do not switch off from the mains) this will save your settings for the present

 

[anuragn]

I will open and check inside for a battery, in which case the solution will be very easy...just replace the battery.
But I wonder why the user manual says that keeping it switched off for more than a few hours would result in loss of memory. If there was a battery, there would have been no need to keep it always on.
By the way, if somebody has download credits for s-100manuals.com and downlaod the service manual for me. On this webiste, they are asking for $4.99 for downloading 50 files and not per file basis.

 

[gobble]

I will open and check inside for a battery, in which case the solution will be very easy...just replace the battery.
But I wonder why the user manual says that keeping it switched off for more than a few hours would result in loss of memory. If there was a battery, there would have been no need to keep it always on.
By the way, if somebody has download credits for s-100manuals.com and downlaod the service manual for me. On this webiste, they are asking for $4.99 for downloading 50 files and not per file basis.

Stay away from such scam sites!! These sites trawl commonly available free stuff floating on the net organize it and score in search results.

the same stuff can be had for free if you search more.

--G0bble

 

[omishra]

Hi
I dont think there is a battery or capactor but an EPROM saving the necessary changes when tunning your stations, the only suggestion I have is to keep the set on standby (do not switch off from the mains) this will save your settings for the present

Then it should not get lost if stored on EPROM. My Sony radio has this feature, it retains memory forever until changed my me. No issues with battery removal for 6 months duration.

My pioneer tuner has large cap with some small voltage on it 2.2 or 5 V. It retains it for even 10 days. Only if I discharged that then stations are lost. So look near the tuning section, there must be some small voltage big cap or get the chip number where tuning button are connected, find its pin out which will tell which cap to look.

 

[sonicbliss]

But I wonder why the user manual says that keeping it switched off for more than a few hours would result in loss of memory.

An EEPROM retains memory for a very long time. If your device indeed used an EEPROM then the manufacturer would not have mentioned the above in the manual.

So it looks like the device relies on a capacitor. There are indeed capacitors that can be used this way. If I am correct they are also called super cap. Here is one such cap:-
http://www.sparkfun.com/datasheets/Components/General/ABC0000CE19.pdf

It is interesting to see that this capacitor itself looks like a battery.

Sonicbliss

 

[quad]

A capacitor does not hold charge for a long time. 2-3 days is out of the question.

Cheers

For many years now, high-capacitance supercaps have been available.
They are used for backup power like real time clock, tuner memory etc.
See the last link - real time clock may get nearly 200 hours backup with
a supercap!

Super Capacitors

http://en.wikipedia.org/wiki/Electric_double-layer_capacitor

http://www.maxim-ic.com/app-notes/index.mvp/id/3517

An EEPROM retains battery for a very long time

An EEPROM will not use battery at all to retain memory.

 

[anuragn]

So look near the tuning section, there must be some small voltage big cap or get the chip number where tuning button are connected, find its pin out which will tell which cap to look.

This is a good idea. Will try and do that.

 

[gobble]

Sound advice by more knowledgeable folks :clapping:

--G0bble

 

[anuragn]

So finally opened up the cabinet and found one capacitor with value marked in F instead of the usual microF (0.047F). I suspect this one to be the "super cap". The voltage is also 5.5V which seems ok for digital application.
Can somebody confirm and suggest what to do next? Will I get a similar one in the market easily.
If I solder another similar one in parallel, it will increase the total capacitance and hence the backup time.

 

[omishra]

Can somebody confirm and suggest what to do next? Will I get a similar one in the market easily.
If I solder another similar one in parallel, it will increase the total capacitance and hence the backup time.

I think you replace that with nichicon made 4700uF/10V, match polarity and see. Still this is trial and error method until you trace the chip where it is connected and look into its datasheet - pin diagram.

 

[anuragn]

I think you replace that with nichicon made 4700uF/10V, match polarity and see. Still this is trial and error method until you trace the chip where it is connected and look into its datasheet - pin diagram.

Should it not be 47000 and not 4700? (0.047F=47000uF)
Anyway, I doubt 47000uF is available.

Pardon my ignorance, but why nichicon and is it available in the market?

 

[omishra]

Pardon my ignorance, but why nichicon and is it available in the market?

nichicon has caps with low ESR are useful for power supply requirements which is supposed to be requirement here.

 

[linuxguru]

There are supercaps available in the market from 0.01F to a few Farads, with voltage ratings from 2 to 5.5V. Manufacturers include Sanyo, Panasonic and Toshin (?). Use the same or higher voltage rating, and a similar (not necessarily identical) capacitance.

The cap should run between Rs.10-50, depending on the value. Generic aluminium electrolytics *will not* work in this application, regardless of ESR, etc.

 

[gobble]

There are supercaps available in the market from 0.01F to a few Farads, with voltage ratings from 2 to 5.5V. Manufacturers include Sanyo, Panasonic and Toshin (?). Use the same or higher voltage rating, and a similar (not necessarily identical) capacitance.

The cap should run between Rs.10-50, depending on the value. Generic aluminium electrolytics *will not* work in this application, regardless of ESR, etc.

Hey Linuxguru (your handle should have been ElectroGuru hyeah

Please educates us as to why?

To the OP something to guide the replacement: A brief HOWTO on replacing electrolytic capacitors in solid state vintage audio equipment

HTH
--G0bble

 

[anuragn]

Hey Linuxguru (your handle should have been ElectroGuru hyeah

Please educates us as to why?

To the OP something to guide the replacement: A brief HOWTO on replacing electrolytic capacitors in solid state vintage audio equipment

HTH
--G0bble

Thanks gobble. But this only talks about electrolytics and not super caps.
It was 22-23 years ago that the first time I started "playing" with electronic components and there cannot be an easier job than replacing a cap (for an experienced diyer) hyeah:
Anyway, need to find some time to go to market and search for an appropriate super cap and will then update.
I think electrolytics cannot be used in this application because they cannot hold charge for too long due to internal leakage (of current).

 

[gobble]

Thanks gobble. But this only talks about electrolytics and not super caps.

what changes for soldering a supercap?

It was 22-23 years ago that the first time I started "playing" with electronic components and there cannot be an easier job than replacing a cap (for an experienced diyer) hyeah:

who is Mr. D. Iyer?

--G0bble