[W126 Coupe] Suspect OVP relay

[Vance Rowley]

I might just do that Mike. Of course, the other possibility is that my DMM hasn't got enough voltage when measuring the forward-bias, but I am sure I have used it in the past on semiconductors, or was that my old analogue meter (memory going). I will have a hunt around the house to see if I can find my old meter and measure again.

Regards,

Vance.
  ----- Original Message ----- 
  From: Mike R. 
  To: 'Vance Rowley' ; 'Mercedes Coupes Mailing Lists' 
  Sent: Saturday, June 13, 2009 5:17 AM
  Subject: RE: [W126 Coupe] Suspect OVP relay


  I think you're right about a bad reading and that a 1N4007 has the PIV rating to handle the relay. If it was mine, I solder in the diode and give it a go.

   

  Later,

  Mike R

   

  From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com] On Behalf Of Vance Rowley
  Sent: Friday, June 12, 2009 9:01 PM
  To: Mercedes Coupes Mailing Lists
  Subject: [W126 Coupe] Suspect OVP relay

   

  Just a quick update. I opened up the OVP and inspected the solder joints. Looked OK, but went over the joints with some fresh solder anyway. Plugged it in, but unfortunately I got the same results. The ABS/ASR lights still on and the high rpm. I did notice one thing though while I was going over the pc board with my meter. That is the small diode that connects to the relay coil itself from pin 15 (no number on it, but looks like a 1N4001) was very high resistance at around 9.6M while testing in the conductive direction. The other direction looks fine and measured O/C as it supposed to. This of course is possible, depending what kind of diode it is, but usually when using a diode this way with a relay coil, a 1N4001-1N4007 should do the job, which of course doesn't measure anywhere near as high as 9.6M in the conductive direction. 

  If anyone knows exactly what this diode is and what it should measure, please let me know. I might just swap it out for a new one before I place the order for my new OVP.

   

  Regards,

   

  Vance.

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