[W126 Coupe] Long Term Battery Drain Problem Solved

[Vance Rowley]

Hi Robert, I am pleased there are some members that take an interest in these kind of problems. It was driving me nuts for ages. Especially as mine was so intermittent. Most of the time when I was measuring the parasitic current it would show only around between 50ma and 80ma which of course is fine.There were only a few occasions that I measured this 6Amps while having the meter connected and not seeing anything powered up. I am so pleased it's all over now.
Thanks for the tip, I might have a go at repairing my old unit.

Cheers,

Vance.
  ----- Original Message ----- 
  From: Robert Karl Stonjek 
  To: MB Coupes 
  Sent: Sunday, May 07, 2006 2:50 AM
  Subject: Re: [W126 Coupe] Long Term Battery Drain Problem Solved


  I would just like to say thanks to all that gave me ideas what to look for and where for the long term battery drain problem I have been having literally for years (although you wouldn't know if you used the car on a daily basis). For those that did take an interest (I know there was a few that didn't and voiced their opinions abruptly) I thought it might be useful for the group to let you know of my findings, as it is the most unusual cause, and who knows, if it can happen to mine, it could happen to another one of these cars somewhere.

  <Snip>

  Thanks again and I hope this info might be of use to someone else someday.
  Cheers,

  Vance
  1991 Euro 560 SEC.

  RKS:
  I had a battery drain problem, just a couple hundred milliamps.  It turned out that someone had wired in the automatic antenna incorrectly, which also explained why it never did anything :)  I could test the drain and so see the meter move when the correct circuit was disconnected.

  On the inside light issue, there is a possible hazard that occurs if the wrong value globe is used.  Here is a message I sent to another group on the issue:-

  Inside light doesn't switch off? 
   
  Message:   This fault will occur if a globe that is too big is used in place of the standard 5W type. They are both roughly the same size (the 'festoon' globes) but the 5w is actually a little shorter (of the ones I have on hand.)

  The problem is caused by the transistor, a BD675, overheating and burning out. To correct the problem, the transistor must be replaced.

  To do this, you must remove the inside light housing and disassemble it. This is a little puzzle box but it is possible, with a little cutting of the plastic.

  The transistor need not be the exact same one - any of the NPN 4amp Darlington transistors of the BD range will do - I used a BD681

  I put a 10W globe in by mistake - nice light but it stayed on when the door closed. I could have put a heatsink on the transistor to extend its current carrying capacity, but there isn't that much room under the cover and I was just happy to get it working again.

  Robert

  PS take a copy of this note to your local electronics wiz-kid with the disassembled unit if you're not into soldering :)
   

  BTW since writing this I've thought about using the brighter 10w globe.  You would need to extend the transistor in question out through the case on flying leads and mount it on a small heatsink.  Too much bother unless I have to go into that area again (for some other reason).


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