Problem with tach disassembly : How to remove second circuit board?

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Today I started started on swapping out my 240z 4-wire tach internals for a 280z 3-wire.

I've already figured out the wiring, so that's not the issue here.

Have any of you guys found a trick to getting that second PCB off the back of the tach housing?

In the tach from the 240Z it was glued on by some bondo-looking stuff, and I only managed to get the board off by using a punch on the hardened-putty stuff from behind (and shattering the PCB on the other side of the putty in the process).

This isn't a big deal, since I am swapping it out anyway, but the 280Z tach has the same stuff holding the back board down and I certainly don't want to damage this one too.

Attached is a picture of the stuff in question that was between the back PCB and the housing.

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And here is a picture of the inside of the tach housing. Note : there didn't seem to be any residue left on the housing from the glue/putty once it came free.

[Xargon321]

put it in the freezer for a couple of hours that might make that adheasive contract and come off the circut board BUT it might take stuff with it if is havs any caps or resistors hidden in that stuff

i use this method to remove stock heatsinks off of video cards for comps works good might have to pry a little but not to hard your youll rip stuff off with it

[Inf]

Hrmm, I think i'll give that a try. There aren't any sensitive components mounted in that backplate really, just the power input leads and the negative trigger lead.

If the ~0F of the regular freezer isn't cold enough, I will try getting some dry ice or something and make just the back of the housing cold. I don't want to make the whole thing extremely cold since i'm not sure how the caps and other parts on the main board will take it.

I've been taking a ton of pics so I will probably throw a little writeup together if I get everything working.

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Well, the cold seemed to cause the putty stuff to gum up slightly.

I was able to use some small screwdrivers to pry up the inner edges of some of the holes and pry it out from behind little by little.

Now I just need to wait for it to dry off. It's a pretty humid day today so when I bagged it up and put it in the freezer, some frost developed in the few hours it was in there :stupid:

[LanceM]

Use a hairdryer to dry it off. If you are going to glue it back in use something like superglue, if you use RTV be sure to get something that is compatable with electronics, regular RTV offgasses something that is very corrosisve and will make a mess of the electronics!