How do I get bottom cover off DME

CharlesJones · 04-28-2012, 01:03 PM

Hi all,

I am trying to get the bottom cover off the DME so I can inspect the solder joints to transistor T504. I have read these solder joints are a known problem area, and it has been suggested that they may have cracked and are causing my no-start issue described in this thread:

Power to ignition coil - can I test with multimeter?

What I am having trouble with currently is getting the bottom cover off the DME unit. I have opened up the top cover, and have seen instructions on how to get the two circuit boards apart so they open up like a book, but I can't find out how to removed the bottom cover so I can get to the underside of component T504.

The picture below shows the underside of the DME, and I have circled 8 connectors which I think are hold the cover on - i.e. 4 on each side. I have removed the middle two bolts on each side, but I am having difficult with the connectors in each corner.

The next picture shows a view from the side, with the 4 connecting points circled again.

Looking at the first connector (closest to the front of the DME, towards the left of the photo) it looks like the bolt has a nut on it which must be accessed somehow, and the bolt inside the DME is painted red with something. Please can someone confirm that this bolt definately needs to be removed, and that I need to hold the nut with needle nose pliers or something to remove it? I have shown a closer pic with this bolt circled inside the DME below.

And then the last picture shows the connector at the back corner of the DME, which appear to be a push-together clip similar to that on the 2 posts which hold the two circuit boards together which comprise the DME. This clip is what bothers me most - I can't see how I comes apart. I don't know whether it needs to pop out of the circuit board or whether it comes apart underneath the circuit board somehow, and I am frightened to just pull it incase I break something. Is there a way I need to prize this clip apart somehow?

Many thanks for your help. I find it very scary working with the DME in case I suddenly hear a load "crack" when I am trying to get the thing apart!

All the best,
Charles.

ant7 · ant7's Garage

hi Charles,
if you look there are some black plastic pillers, that is where the two boards split, if your still not sure, go to the steve wong site [911 chips] it is all explained there.
Hope this helps.
Anthony.

Quicksilver · 04-28-2012, 02:05 PM

Your not trying to get it off the bottom plate. Think of the gray ribbon cable that connects the 2 boards together as a hinge. You need to get the top board unhooked from the plastic around the harness connector side and then the "black plastic pillars" split allowing you to open it up.

CharlesJones · 04-28-2012, 02:10 PM

Thanks for your help Anthony. Its the bottom cover I was having difficulty taking off though - I found the instructions on the 911 chips site about how to get the two boards apart, but I couldn't get the bottom cover off.

However, I have got it off now! Those two black plastic clips in the corner have a centre pin which you can just get hold off at the bottom with a pair of needle nose pliers. After removing that central pin I was able to squash the two halves of the clip together on the cover side, and push the clip through using the pliers again.

I also removed the two bolts in the opposite corners - I seized the nut on the circuit board side using needle nose pliers, and then unscrewed the bolt from beneath.

One thing I almost missed what that in one corner only, at the front of the DME, there is also a tab on the cover which was folded over a plastic moulding connected to the black connector which both circuits boards fit into. After removing all 8 connectors I had to slide the circuit board assembly from out of that tab to get the cover off.

Now that I finally have the cover off those solder joints beneath component T504 actually look fine, as far as I can tell. Drat - I was hoping there would be a nice cracked joint around one of the pins! Maybe this hasn't been my problem after all. I just wish I had a another DME which I knew was working to try in the car!

dshepp806 · dshepp806's Garage

I'd (still) reflow the joints......

Best,

Doyle

ant7 · ant7's Garage

hi Charles,
Ahh, understood,
As Doyle said, i would still re-solder those joints, and any others that look suspect, get a realy good eye glass and give the board a closer look, you may be surprised.
Anthony.

88911coupe · 04-30-2012, 09:57 AM

It took my old eyes a LONG time to actually see the breaks when I did this a few years ago. Had to take it on my balcony in BRIGHT sun to be able to see them...they are really faint, at least to me they were. I probably should have taken it to a place that does this for a living but it ended up working out great.

CharlesJones · 04-30-2012, 10:07 AM

Thanks for the comments guys. I buttoned the box back up and put it back in the car, but it looks like I should reflow those solder joints anyway. My problem is that I lack confidence with a soldering iron - I am really have only soldered about twice in my life, so when I saw those neat solder joints I daren't touch them for fear of making a mess of them! However, having read your posts above I am thinking that perhaps I should.

You make an excellent point Buck - I think I might send the DME off to professionals are more used to these things. There is a company in the UK who I have used before (different car) so I might try them. What I think I will do first is troubleshoot everything else on the car so I can eliminate any other causes of my no start condition. With everything eliminated then it can only be the DME, in which case I will send it off to be checked and fixed.