Has anyone taken apart a GM knock sensor amp and drawn up schematics for it? I would like to see if it can be modified to be adjustable.

If not, maybe I will try to find another one and open it up and do so.

thanks,

John.

 

I've opened one up and played with it. FWIW it is built on a ceramic substrate with 'printed on' components. Not sure if the 'printed on' is entirely correct but that's the way it looked.

The assembly was filled with a clear goo. I figured this was for acoustic damping. The resistors were laser trimmed. Fine lines cut through them. The chips (if you want to call then that) were flip dies w/an epoxy coating over them.

Might want to get a newer (LT1/LS1??) module and try that. Also, I don't see a reason why a stock '747/'165 unit could not be re-cal'd. It should be possible.

RBob.

 

I suspect the clear goo is more for protection from oxidation and to keep parts from falling off than damping since the microphone is actually in the sensor, but I could be wrong.

I think the 747 just gets a logic signal from the amplifier doesn't it? If so, then tuning would have to be done in the amp. Or it could be done in the sensor itself, which is apparently how GM does it.

 

There are no components to fall off. I'll see if I can find the one I opened up and take/post a pic.

The '747 gets a low pulse for the duration of the intensity of the knock. The filter is a bypass filter. It detects: a rapid increase in amplitude, a rapid change in frequency, a maximum amplitude. Hook one up on a bench and feed it from a function generator.

RBob.

P.S. Microphonics.

 

Do you know what the bypass filter center frequency and Q are?

I'll have to try the function generator. This is getting interesting.

John.

 

There might be some filter info here you can use(?), if you haven't already seen it:

http://members.tripod.com/lyc_42/eke/eke.htm


Edit: Oops... just opened the site & realizeded the 1st page of the schematic isn't there. Wonder if anyone saved it anywhere else?

 

This is the HKM knock filter. The components w/the lousy soldering are the ones I R&R'd (to measure out of circuit).

The wires along the top go to the connector. The black objects are resistors. Close look will reveal the laser cut trim lines. The blue are insulating pads. The silver are traces.

RBob.

 

Cool.

Did you draw out a schematic?

 

Had to scrounge around for my notes. No, didn't do a schematic. I thought I had started one but can't find anything.

RBob.