[T3] OMG, My BRAIN died!

[Jim Adney]

On 5 Jul 2013 at 20:55, Keith Park wrote:

> Put the spare brain on and Walla!  Everything works!  Even put the old
> one back to make sure it was still bad and it was. this is the FIRST
> bad Control unit Ive ever had On any of my cars, and other than the
> fuel pump relay it was still working fine..  Always carry a spare! 

Look in the opening at the end of the brain. Hold it flat, with the 
PC board on the bottom. There's a TO-39 transistor inside, just past 
the edge connector, on the right hand side. Sometimes they have a 
heat sink snapped on them (probably a good idea.) This is the 
transistor that provides the fuel pump relay ground.

Look at that transistor. Sometimes they are mounted off the board 
with a plastic 3-pointed spacer and sometimes they have a little 
spongy red rubber mat pad underneath them. If yours has the rubber 
mat, it's possible that this has held moisture against the leads and 
caused the leads to rust thru. (Yes, the leads are plated iron. You 
can check with a magnet. You can tell if a lead has rusted thru by 
trying to gently move the body of the transistor. If all three legs 
are still intact it will be sturdy. If not, it will wiggle easily.

The transistor could also have lost an internal bond wire. That 
sometimes happens to those old style metal cased transistors.

To provide a ground, I believe that would be an NPN. You can take the 
cover off and replace it. You can probably get another 40 years out 
of a similar TO-39, or move to something more modern. Pick anything 
that can handle 20 V and 150% of whatever the relay draws. I just 
grabbed something from my stash. I have more if you need one.

I've replaced exactly one of these. The hardest part was getting the 
cover off and back on. You'll have to unscrew the board and hinge it 
back on the ballast resistor leads to get at the underside of the 
board, but that's easy.  

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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