Comand won't remember the setting
 

hi guys,

i'm new to this board. I just wondering whether anyone here has experience the issue with comand won't remember the sitting like bass/treble, radio station, etc. I can change the Bass/treble setting on my e coupe, but once i turn the car off for about 30 min, when i start it back on, i won't remember my bass/treble setting. it will go back to the default setting. Plus, every time i start my car, it will first start of with music register rather than the last source that I used (E.g. CD/ Radio). Anyone experienced this problems, you kind comment is greatly appreciated in advance.

I talked to the tech that works on my cars from Brumos today about your problem, and he said that your constant/12 volt wire (many refer to it as your memory wire) has lost connection, blown a fuse, etc. Your ignition power wire is still receiving power, so it allows you to turn your radio on when the car/ignition is on. The radio has a small capacitor in it that acts somewhat like a battery, so after you have the radio on for a short amount of time it will energize the capacitor which mimics the memory wire and will allow your radio to keep the settings for about 30-40 minutes. When you turn the ignition off, the capacitor discharges it's energy after a short amount of time which makes you loose it's settings.

Your radio receives power from two different wires:

1. Constant=12 volt wire that receives power from the battery around the clock, even when the car is off which enables the radio to remember your settings.

2. Ignition=12 volt wire that receives power when you turn the ignition on, which also turns on your radio.

He said you should take it to the dealership or an audio shop to have it checked out because it might be a relay or something important related to another system that the constant wire is also related to (but will be an easy find for them), but if you ignore it you could possibly cause damage to other systems. I know it isn't the best answer, but I thought I would ask for you.

The above could be true for an old radio but if I interpret correctly the E coupe 250, it would be the current model where the head unit does not have switched power at all and the head unit cannot be running on switched power alone.

Perhaps the OP could clarify the car model details.

I know mine wasn't the best answer, but I thought I would ask the tech for him. Even the simplest of components such as a stereo in these cars are getting over complicated by the manufacturers these days. I miss the days when something didn't work, and the remedy would be as simple as locating a blown fuse... I guess I am just getting old.

We all are!! Radio should turn on with CAN, even on an older radio vehicle prior to CAN or MOST the tech would be out of his mind. Plus the size of the capacitor/cap would require a special compartment alone as it would be bigger than the radio, and amp, and speakers... however I did have the luxury of blowing up 15 farad cap (the itty bitty caps inside were polar, and installed wrong... 4th of july and stained my drawers)

thank you all for your kind respond. My benz model is 2012 E 250 coupe, it comes with Harman Kardon and NAV Comand. I'm bring the car to the shop tomorrow, and hopefully they will be able to fix it.

Not quite true. It is not uncommon to see use of a memory backup capacitor (as an alternative to a lithium, battery backup or a flash chip) in electronic equipment and devices to maintain preset information when the power is removed or failed. These capacitors are special memory capacitors which retain a charge for very long time, usually providing a low voltage to a chip or circuit responsible for settings etc. Though rare, these capacitors can fail due to environmental reasons. Identifying and replacement of these capacitors requires knowlege of electronics, made easier if you have a circuit diagram. I have only ever had need to change this capacitor once in my lawn sprinkler control system.

nope :sadwavey:

yes, but still no :)

[QUOTE=jbondox;5956148]yes, but still no :):rolf::rolf::rolf::rolf:

Not trying to be rude, but you are thinking of a completely different type of capacitor. The kind you are referring to would be like a "one farad capacitor" that many people use on large stereo system in line with the battery to keep it from a constant load killing/drain happening to the battery of the car. These are huge, anywhere from the size of a coke can to a small fire extinguisher.

The capacitors we are referring to are anywhere from the size of 3/8" (or smaller), to the eraser on a pencil, on up to a quarter, and bigger. Just look inside of any car stereo, or for that fact any piece of electronics and you will see them. Trust me if they did not exist, lol 99% of the electronics in existence would not be around. The really small little disc, or cylinder shaped pieces that you see soldered onto any circuit board, and are usually folded over, are made of ceramic, glass, etc., and they can be smaller than an eraser, and they make many many more smaller and larger than that. In college this was one of my favorite things to do a paper on because my prof's loved early geeks that likened to have almost blown themselves up trying things out lol.

In 1745 Von Kleist stumbled upon the basic properties of the capacitor, and in 1746 the Dutch physicist P Van Musschenbroek came up with a similar device that was more refined which he named the leyden jar (a basic capacitor) and he named it after his University of Leiden in France. Daniel Gralath was the first to combine several leyden jars via a parallel defined structure, which gave the world it’s first “battery”. Later Ben Franklin gained the ultimate notoriety by ripping off all of their work by basically saying "lookie what I did... cough bs cough bs".....


This is just a quick search reference that should give a little clarity to what we are referring to:

http://www.mikroe.com/old/books/keu/02.htm

I wasn't trying to be a smart** with this, I'm just a geek with a few toys:smash:

I will tear about the comand and let you know what I find :)

From what I remember that it was just all eprom as that is why all the radios factory and aftermarket are connected to constant power to maintain the heart beat. I will tear into one in the near future along with a Kenwood or something.

I was going to build a radio system a few years ago and spent some money with China on design, I never seen anything referenced to it in the schematics or circuit descriptions as a memory cap. I could be wrong and yes I was referring to the aftermarket fire extinguisher type :)

It is not a user servicible part and I have never seen a memory capacitor referenced in any device it is installed it. One just needs to know which capacitor, if any is a memory capacitor, especially if the person servicing equipment is knowlegeable about memory retention methods in respective devices.

An Eprom or Flash memory does not need power when switched off, it is non-volatile; both devices are electrically erased/programmed however these devices are not useful in areas requiring frequent programming. Reprogramming an Eprom requires it to be completely erased then progammed; a Flash memory can be partially reprogramed.

An Example:
A volatile memory, such as one required for storing the older computer's BIOS settings may be stored in cheap CMOS memory because a CMOS is easily programmed/partially/completely etc. and requires a very very low voltage and current (from an external source) to retain memory (BIOS is stored in an EPROM/Flash memory). Computers may use a Lithium battery for CMOS backup power, where a lithium battery has a life expectancy of 10+ years however will eventually need replacing. A cheaper alternative (in other electronic devices) is a memory capacitor, which can potentially last a lifetime except in rare cases, where it may fail.
Note: Computer BIOS settings don't have to be stored in a CMOS, modern computers store BIOS settings in an NVRAM.

When I was looking at building a new radio for the C (W204), I had a complete parts break down of the circuits and description. So I am sure I would of seen it since I read it front to back several times. Its been a few years but I am sure it is around somewhere.

Harman Kardon are notorious for using memory backup capacitors it appears. A little research confirmed that.