02-20-2007, 04:06 PM
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Registered User
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Join Date: Dec 2000
Location: Long Island, NY
Posts: 4,358
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Found it!
Thx to somebody reminding me about archived websites....
http://web.archive.org/web/20010618183627/www.mbz.org/articles/ignition/bbox.html
...All of which, I will quote verbatim here...
Quote:
MBZ.ORG - How to Fix 350/450SE V8 Spark Boxes
By Rob Dickinson
I wish to share a bad experience turned great for us. My Dad had an ignition failure with no spark. The MB agents wanted a small fortune for the "Spark Box" and my elderly father was obviously upset about it. The Mercedes Dealer located the only new one to be found in the country then. My Dad, clutching at straws, mentioned that his son was in the electronics business and asked if he could return this box for credit if I could fix it. With a smile they agreed. You guessed it, on opening up the aluminium extrusion, alI I saw was an array of Bosch numbered components.
A quick multimeter check on "Diode" mode revealed that the largest transistor TO3 Can was open circuit. The search for an obscure (probably In-House) Bosch number revealed nought. Common logic was that this transistor was the main output one that drives the coil, so it had to be worked very hard and had to be beefy. I looked for the highest current and voltage rated, physically equivalent heat sink mounted TO3 can package (Oval shape secured by 2 screws, for those not in the business) NPN transistor that I could find. The 2N3773 I put in there worked! The MB Dealer couldn't believe it, he honoured his credit offer and refunded my Dad. (The actual spec on a 2N3773 NPN Transistor is 140Volt 16Amp).
I also must mention that I checked the passive components around it, all caps etc OK. Nearly 10 years later and this "Spark Box" is still working! If anyone has an old 350 or 450SE V8 and a broken "Spark Box" in the garage cupboard, it is worth a try to spend less than 5 US$ and resurrect it as a spare. I am not going to accept any responsibility for damage anyone may inflict, however as I see it, you will know instantly whether it works or not. If it doesn't, throw the box out.
Rob Dickinson
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-CTH
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