I'm trying to repair an FM radio, previously it stored the saved frequencies. When you unpluged it and plugged it back in the stored channels remained. Now when you unplug it they gone.
I want to repair this, but have no clue on what could be wrong, how does it store these channels. I looked for a battery / big cap but nothing. Any idea ?
I'm trying to repair an FM radio, previously it stored the saved frequencies. When you unpluged it and plugged it back in the stored channels remained. Now when you unplug it they gone.
I want to repair this, but have no clue on what could be wrong, how does it store these channels. I looked for a battery / big cap but nothing. Any idea ?
As you say, it's usually a battery - often a slim Lithium cell, soldered on the board somewhere.
Other options are a large capacitor (but only for short term memory), or an EEPROM - but these are fairly uncommon in FM radio.
Assuming you do find a lithium battery on the board?, be VERY careful removing it - I presume it's caused by leakage from the battery?, but the solder tends to 'explode' off the board when you apply the soldering iron, it can easily hit you in the eye (I wear glasses, and have had solder splashes on the lens more than once!).
I know my little AM/FM radio only uses a relatively large cap to keep my 6 memorized frequencies on some sort of volatile memory. If my batteries go dead and don't replace them quickly I lose my settings. Might just be a faulty cap?
Not sure if it's true or not, but in a computer class that I took, they said that some BIOS chips have batteries built into the chip, so when the computer starts forgetting, you have to replace the whole BIOS. Maybe it's the same for this?
I opened my little portable Sony AM/FM radio with 5 channels memory in the hope that I could find something that could help you. Unfortunately, what I saw is mostly one big 1000uF 6V cap (the radio operates on 2x AA/LR6), one proprietary Sony IC (with the top painted black so no markings are showing) and the rest looks like the normal analog RF stuff. No other strange looking IC...
While I dismantled it with the batteries removed, it was flashing a "no power" logo on the LCD for about 2-3 minutes, and then it stoppped. When I put the batteries back, the preset channels were gone. So it looks like on my radio, the big cap and the unknown IC are doing the storage job... Sorry.