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Quote:
Originally Posted by old man neri View Post
Well, this morning I jiggled as many things as I could to get it to stall and only stalled once when I really shook the FW speed sensor. I think I actually unplugged it by accident because I was shaking too hard.

I opened up the DME brain and noticed this.




I resoldered the three. We shall see what happens.
That's it! Just resolder those connections.
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Old 07-05-2018, 08:46 AM
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Double post.
Old 07-05-2018, 08:52 AM
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Day 1 after the resolder. No events so far. Here's to hoping.
Old 07-05-2018, 07:36 PM
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Which solder was bad?
Can someone identify what is wrong in this photo?
Curious how to identify good vs. broken solder.
They all look the same to me.,
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Old 07-06-2018, 06:39 AM
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Looking from my cellphone, it appears 3 and 5 are cracked. See the darker parting lines half way up the Ďmountainí?
Old 07-06-2018, 06:47 AM
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3 and 5 looked bad. It's a zoomed in cell photo so it's hard to tell. I redid 3, 4, and 5.

Here are some pictures from other people of what a bad solder joint could look like on the ECU.





Good short thread on the subject:
DME Bad Solder Joint Repair


Last edited by old man neri; 07-06-2018 at 07:06 AM..
Old 07-06-2018, 06:59 AM
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Solder joints should look shiny and smooth like 1, 2, 4, 9. Even 10 and maybe 11 looks like it might be breaking.

The larger the part being held on by solder the more chances of this happening.
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Old 07-06-2018, 07:09 AM
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Quote:
Originally Posted by sugarwood View Post
Which solder was bad?
Can someone identify what is wrong in this photo?
Curious how to identify good vs. broken solder.
They all look the same to me.,
There's at least 2 pads that are cracked, and a few suspect looking ones. There's about 7-8 pads in that photo that I wouldn't be able to resist re-working once I was sitting there with a de-solder pump, an iron and a reel of multicore...

A lot of Bosch solder work from the period was just awful. Solder joints should look smooth and shiny. And a fresh one is bright and shiny. That last will oxidize and dull over 4 decades - especially as that is "real" solder (== "contains lead").

But rough, dull and lumpy? No good solder joint looks like that. It's sort of like welding; once the joint is up to temperature, the metal is hot enough to flow and gets wicked in - at the same time, the flux burns off, because its done its job..

Another dead giveaway is big puddles of flux around all the solder pads - like my Bosch climate control had...

Did the factory do better solder work on that Motronic, or did they just wash the excess flux off with solvent? I know which way I'd bet...

Worth pointing out that reflowing your solder joints can also affect how willing someone might be to repair the unit later; many of those components can be damaged by excessive heat, and an expensive electronic box probably not the best place to learn that skill.. But it's not difficult, exactly.
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Old 07-06-2018, 07:45 PM
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Ya, I only did the 3, 4, and 5 for a few reasons. 1) They have repeatedly been shown the community to be an issue, 2) Two of them were actually cracked, 3) They would have the highest tolerance for heating and soldering by an amateur without causing damage.

The others looked fine to my untrained eye. Keep in mind you are looking at a low quality cell phone photo. As for the original Bosch quality, well, it's 30 years old before it started giving me issues. As for your last point about monkeying with it and then not being able to get a pro to work on it, that's a fair point. I will keep that in mind.

In the mean time day 2 had no issues as well. I am almost cautiously optimistic but the pessimist in me still doesn't think I fixed it.
Old 07-07-2018, 05:27 AM
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In 1986, how were these solder joints done? By a robot?
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Old 07-07-2018, 07:24 AM
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Usually circuit boards were mass soldered with a 'wave table'. Board would be held above the pool and a 'wave' would wash the bottom of it in solder, fusing all the points at once.

It's actually quite common for any old solder joint to eventually crack due to vibrations and road use. Older BMWs suffer from this as well, either from the DME, the gauge cluster, the Info Panel, even the warning panel in my friends 88 RX7 had these issues (his clock worked half the time due to this issue). I took aviation classes in college and learned the art of repairing electrical circuits and 90% of the time all these Gremlins were fixed by a simple reflow..
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Old 07-07-2018, 08:49 AM
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Quote:
Originally Posted by spuggy View Post

A lot of Bosch solder work from the period was just awful.
Actually that's not true. These fatigued solder joints shown in the pictures resulted from vibrations
and how components were mounted to/on the circuit boards. Besides, mounting the DME ECU
on the vehicle's floor under the seat didn't help. No other areas of the circuit boards on the 911 3.2
DME ECU rarely if ever fails. Please, no guessing.
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Last edited by mysocal911; 07-07-2018 at 09:08 AM..
Old 07-07-2018, 09:05 AM
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Yep, thereís no vibration protection on these old DMEís.

Add taught, filling-rattling suspension, and itís a recipe for cracked joints.
Old 07-07-2018, 09:40 AM
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Quote:
Originally Posted by Tippy View Post
Yep, thereís no vibration protection on these old DMEís.

Add taught, filling-rattling suspension, and itís a recipe for cracked joints.
And, mounting ECUs horizontally, i.e. parallel to circuit boards, asks for problems.
Later Porsches (986/996) had the DME ECUs mounted vertically, i.e. reduces flexing of the
circuit boards.
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Old 07-07-2018, 09:51 AM
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Great point
Old 07-07-2018, 02:36 PM
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Originally Posted by mysocal911 View Post
And, mounting ECUs horizontally, i.e. parallel to circuit boards, asks for problems.
Later Porsches (986/996) had the DME ECUs mounted vertically, i.e. reduces flexing of the
circuit boards.
Interesting point. Thanks for sharing the insight.

I don't see where else Porsche could have mounted these units unobtrusively though on the 911 given the interior space, or lack thereof.
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Old 07-11-2018, 05:05 PM
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In my case it was broken solder points fixed by Ingo. Has worked perfectly ever since he did his magic. I later ran into a random no start and Ingo helped me isolate it to a randomly failing RPM sensor.
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Old 07-11-2018, 07:00 PM
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Update. It's been a week at the problem has yet to reappear.
Old 07-13-2018, 02:13 PM
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That's why I have been telling anyone that will listen to send the Motronic unit to Ingo during the "off-season", the intermittent issues this can cause will make you crazy trying to chase down.
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Old 07-13-2018, 03:29 PM
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That's why I have been telling anyone that will listen to send the Motronic unit to Ingo during the "off-season", the intermittent issues this can cause will make you crazy trying to chase down.
He's fixed the problem! Can't read what's been posted about the KEY failure mode?
Sorry you wasted your time and money not fully reading and listening to Pelican members and simple DIYs.
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Old 07-13-2018, 07:40 PM
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