Carrera stalling problem ... can you spot the problem?

[Steve W]

The car is an 88 Carrera with ain intermittent stalling/cut-out problem. Swapping in another Motronic DME unit fixed the problem. Below is a picture of the lower board of the Motronic unit (0.261.200.082 / 911.618.111.20). Can anyone spot the problem?

[DRACO A5OG]

Steve? Is this a test?

Sorry I wish I could help you.

Break a Leg man hope you find your issue.

Maybe if you post the known good one next to this one could help some electro guru, my .02

[KCinBR]

Cold solder joint.....WHAT DID I WIN?????????

[dshepp806]

There are several joints that look suspect...I'd reflow 'em and see.

What is that crap in the upper left hand section of the pic? Doesn't look like flux to me.

Best,

[PeterTarga]

Bad solder on the right, seems to be broken.

[Bill in OKC]

I see a few places that look suspect. A cold solder joint, a posible solder bridge and a couple of places where it looks like vibration or thermal could have broken the solder joint - looks like a ring around the joint.

[dshepp806]

There are several joints that look suspect...I'd reflow 'em and see.

What is that crap in the upper left hand section of the pic? Doesn't look like flux to me.

Best,

[dshepp806]

Originally Posted by Bill in OKC

I see a few places that look suspect. A cold solder joint, a posible solder bridge and a couple of places where it looks like vibration or thermal could have broken the solder joint - looks like a ring around the joint.

Specifically: the 2 joints circled, lower right. classic cold joints, as one can see the circular fracture footprint.

Best

[rick-l]

Is this one?

[mhoffman]

Whatever the yellowish precipitate is in the top right- looks like some leakage from above(?) If it dissolves in water and precipitates out, it probably conducts electricity...

Also that one darkened solder joint looks like is got a bit too warm- what is the component above it? It may have failed...

[3.2 CAB]

I actually lost count of the number of "cold solder joints" along with a couple or spots that look like they got too hot. Tony.

[cgarr]

I want to know what camera you used??

[burgermeister]

I see many cracked solder joints. I see some possible bridging of joints by goo or corrosion (or just leftover rosin from a previous repair) by the 2 cutouts in the board. And I see odd yellow chalky stuff in the upper LH corner - is it a solid version of the "magic smoke" that makes electronic componentry work?

[Steve W]

Originally Posted by DRACO A5OG

Steve? Is this a test?

Sorry I wish I could help you.

Actually I hoped Loren would chime in . . .

Originally Posted by KCinBR

Cold solder joint.....WHAT DID I WIN?????????

Keith, I'd send you a box of chocolates, but since you weren't more specific, you only get a cookie. Shoot me your address and I'll get it right out to ya.

Originally Posted by dshepp806

There are several joints that look suspect...I'd reflow 'em and see.

What is that crap in the upper left hand section of the pic? Doesn't look like flux to me.

Not sure, could be glue, or cat pee - let me taste it and I'll get back to you.

Originally Posted by PeterTarga

Bad solder on the right, seems to be broken.

... lemme see, you may be right

Originally Posted by Bill in OKC

I see a few places that look suspect. A cold solder joint, a posible solder bridge and a couple of places where it looks like vibration or thermal could have broken the solder joint - looks like a ring around the joint.

Doyle, you are a genius - yes those two lower joints you circled are indeed fractured.

Originally Posted by rick-l

Is this one?

Rick, although that joint does look a little dark, it looks pretty solid.

Originally Posted by mhoffman

Whatever the yellowish precipitate is in the top right- looks like some leakage from above(?) If it dissolves in water and precipitates out, it probably conducts electricity...

Also that one darkened solder joint looks like is got a bit too warm- what is the component above it? It may have failed...

Matthew, that is pretty spot on. There is some white crap on the other side of the board around the DME connector pins that look like corrosion from a liquid. That component above the dark joint is the big gray resistor, R528. It looks OK, typically when something overloads them, they look completely burned out.

Originally Posted by cgarr

I want to know what camera you used??

LOLs, that camera is a HP scanner - although I think a Canon SD950is is a fantastic compact.

Originally Posted by burgermeister

I see many cracked solder joints. I see some possible bridging of joints by goo or corrosion (or just leftover rosin from a previous repair) by the 2 cutouts in the board. And I see odd yellow chalky stuff in the upper LH corner - is it a solid version of the "magic smoke" that makes electronic componentry work?

Ever since since Lucas stopped selling magic smoke, I've been trying to find a new source, but no luck yet.

[Steve W]

Here's a closeup of those cracked solder joints:



It belongs to the big metal transistor, T504 right above it that you see outlined in the picture below. This is a common failure point for these DMEs - the solder joints crack from heat/fatigue/overloading. This powers/charges the ignition coil and when the joints crack, you will get an intermittent connection from a joint that expands and contracts. When cold, your car may start, but when it warms up from the current flow, the joint will expand and the connection will break. When a car starts having problems starting, or cuts out while driving, this area should be checked, in addition to the DME relay.

[fumanchu]

Had the exact same transistor burn up in a 951 DME with the same cutout/stalling characteristics as Steve pointed out. Left me stranded on the side of the road on the way back from Laguna Seca. The TV repairman who cold soldered it for me found another 30 or so cracked joints in there. Seems to be common as the DME's get older.

[acapella8]

subscribing, when I get a 951, I am going to need this. . .

[DRACO A5OG]

Oh my, Great post thanks Steve.

[dshepp806]

always the higher power components,....heat's the enemy,..AMEN!

Best,

[ianc]

Great post Steve!

Posts like this kinda make me want to just take my DME out and examine it very closely. However, I have found, after a recent DME relay failure, that these cracked joints are not always obvious to the naked eye (at least not 45 year old eyes like mine), so a magnifying glass is a big help.

A question Steve: I've read of a fair number of these types of solder fractures, and they seem usually to lead to intermittent starting or running of the engine. Based on your knowledge of the DME internals, are there any such fractures that would not lead to a complete engine cutout or start failure, but instead to poor running condition of some kind?

I wish someone would compile a kind of manual of the DME itself: what each component does, and what its failure might cause.

ianc