Tachometer Amplifier Schematic? - Page 2 - PeachParts Mercedes-Benz Forum

boneheaddoctor · #16 02-20-2005, 01:01 PM

Quote:

Originally Posted by MTUpower

I have half a dozen of 617-95X tested tach amps in my tool box. $20 delivered to your house.

You have a PM............

barry123400 · #17 02-20-2005, 01:19 PM

Noticed nobody responded to the post awhile ago about tach only working properly when horn button involved? Just a guess but sure would want to check all the grounds in the tach circuit before going further. Especially any multiple ground point should be cleaned up. Does the horn have to blow for the tack to function or just contact with the horn button enough?

#18 02-21-2005, 02:44 AM

If you have a Mercedes 300D or 300SD and your tachometer bounces around and works randomly, try this: On the left inner fender well in the engine compartment you'll find a round black, screw-on cap (this is your tach amplifier). Unscrew this cap and remove the rubber o-ring and screw the cap back on tightly. By removing the o-ring, the contact pins in the cap will penetrate deeper and make better contact and will probably fix your tach problem. Could it be any cheaper or simpler than that?

scott2go · #19 02-21-2005, 04:59 AM

Quote:

Originally Posted by MTUpower

I have half a dozen of 617-95X tested tach amps in my tool box. $20 delivered to your house.

You have pm/email

mplafleur · #20 02-21-2005, 06:18 AM

Quote:

Originally Posted by mattdave

If you have a Mercedes 300D or 300SD and your tachometer bounces around and works randomly, try this: On the left inner fender well in the engine compartment you'll find a round black, screw-on cap (this is your tach amplifier). Unscrew this cap and remove the rubber o-ring and screw the cap back on tightly. By removing the o-ring, the contact pins in the cap will penetrate deeper and make better contact and will probably fix your tach problem. Could it be any cheaper or simpler than that?

Or you could put some dielectric compound on the pins...

Doktor Bert · #21 10-27-2005, 04:50 AM

Quote:

Originally Posted by boneheaddoctor

Tach amp for a '79 300SD is the same as my '83 300D its the miniture black garbage can on the drivers side front fender.

Hmmmmm....are you referring to the cap on the diagnostic plug???...Bert

boneheaddoctor · #22 10-27-2005, 08:01 AM

Quote:

Originally Posted by Doktor Bert

Hmmmmm....are you referring to the cap on the diagnostic plug???...Bert

..no the W123 (except for 1985 I understand) and W116 use the same trash can style tach amp on the left front fender...about the size of a huge Pill bottle.

dieseldiehard · #23 10-27-2005, 12:14 PM

Quote:

Originally Posted by boneheaddoctor

..no the W123 (except for 1985 I understand) and W116 use the same trash can style tach amp on the left front fender...about the size of a huge Pill bottle.

Herr Doktor Bert is right, the socket the garbage can looking plug (with tach amp) goes into is called the diagnostic socket which an external diagnostic tachometer can be plugged into that indicates engine speed and maybe a few signals (but nothing like the computer readout stuff on modern cars which are more like a heart monitor setup you'd find in an operating room in a hospital!) the cap is itself also the tach amplifier.
I would love to see a schematic of one of these (bump!) but VDO apparantly has never published one

boneheaddoctor · #24 10-27-2005, 12:23 PM

Quote:

Originally Posted by dieseldiehard

Herr Doktor Bert is right, the socket the garbage can looking plug (with tach amp) goes into is called the diagnostic socket which an external diagnostic tachometer can be plugged into that indicates engine speed and maybe a few signals (but nothing like the computer readout stuff on modern cars which are more like a heart monitor setup you'd find in an operating room in a hospital!) the cap is itself also the tach amplifier.
I would love to see a schematic of one of these (bump!) but VDO apparantly has never published one

I've never sat down and torn one appart to try to reverse engineer it...maybe if I get bored this winter...

dieseldiehard · #25 10-27-2005, 12:34 PM

Quote:

Originally Posted by boneheaddoctor

I've never sat down and torn one appart to try to reverse engineer it...maybe if I get bored this winter...

I started to cut one open but when I found the solder side is covered with a encapsulation junk I figured the inside is probably full of it too, making the job a lot more difficult that it would be otherwise.
That would be a nice winter project wouldn't it? I hope you start off with a big pot of coffee

#26 10-28-2005, 04:43 AM

The online FSM has it in the electrical section. Oddly enough the red/black wire on the tachometer gauge goes to the glowplug timer.

math · #27 03-27-2021, 12:12 AM

So, did anyone get the schematic for these ? i'd love to make one as you just cannot get these anymore

Mike D · #28 03-27-2021, 06:43 AM

Anyone know what happened to Bob (Techguy512)?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Climate Control Schematic	Corby	Tech Help	2	04-19-2013 08:47 AM
tach amplifier schematic?	rs828	Tech Help	1	02-19-2005 08:46 PM
tachometer amplifier p/n number	tls	Diesel Discussion	1	08-30-2002 05:36 PM
cruise amplifier schematic	240Joe	Tech Help	1	05-20-2002 07:51 PM
cruise amplifier schematic	240Joe	Diesel Discussion	0	05-20-2002 08:40 AM