How this Automatic powr on off circuit working?

Discussion in 'General Electronics Chat' started by mhtplsh, Dec 29, 2010.

  1. mhtplsh

    Thread Starter Member

    Jul 29, 2007
    Herewith attached the automatic power on circuit of an car audio. It is used as auto power on when there is audio input. Audio amplifier starts working after some time of audio signal input.
    When there is no signal for 30 seconds it becomes automatically off.

    This circuit is not becoming off after 30 seconds. many times it is on for long hours in car even when audio signal is not present. Kindly explain me how to modify or remove this problem. So please guide about working of this circuit.
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    What are the DC power supply pins on U2 connected to?

  3. marshallf3

    Well-Known Member

    Jul 26, 2010
    Schematic is too large for me to look at. If it worked at one time then is not now I would suspect some of the electrolytic capacitors which are usually the old 85*C ones and don't last long in an automotive environment, they end up with excessive leakage as well as a loss in capacitance.

    I wish JBL/Infinity had not taken away all their schematics from their website, they had some nice autosensing circuits that worked well for ages. It wouldn't be too hard to design one of your own but fixing this one may be as simple as replacing the key electrolytics with good 105*C ones.

    I think for the heck of it I'm going to write JBL to complain. Even though I downloaded most all of their schematics they may be on an old set of drives that crashed long ago and I'll be darned if I'm going to pay to recover a mirrored drive setup which shouldn't have failed. I lost the mirror when I installed an evaluation copy of Server 2003, it wrote new hard signatures to them and not only broke the mirror but made one appear as failed and the other as foreign. Never have been able to get them back and although there's software out there that claims to be able to recover from that situation I'm not in a position to pay for it. My MIS is retty good at finding stuff like that from the Warez community in which I am scared to venture into because there's so many programs that include embedded malware it isn't funny.

    [EDIT:] Very carefully worded letter sent to JBL, I've got so much of the Harman-Kardon equipment line both home and automotive that it isn't funny. If they'll give me a link to an ftp entry to their servers I'll pull everything down as I can even if I've got to grab another hard drive and make a backup of it but in theory it should all fit on a double layer DVD. I don't really trust the double layer DVDs for really long term storage so I'd probably put it on as many regular ones as necessary.

    BTW: NewEgg has a great sale on TDK double layer discs, something like $26 for a cake box of 50 with free shipping.
    Last edited: Dec 29, 2010