DME help

fastfredracing · 10-13-2010, 06:08 PM

I took in an early Carrera late last week DOA. It has no spark I am next to 100% positive I have a bad coil driver in the DME. I get no pulsing ground to the neg side of the coil. I have good power and grounds to the DME,. good signals out of the ref, and speed sensors, A working DME relay, injector pulse, and I can make the coil spark manually.
I have read some threads in the past about reflowing solder joints. If any of you have any experience in this area, and have some advice to lend, I would appreciate it.
I was just wondering what area of the board I should be looking at . I planned on following the circut from the dme connector and looking carefully with a glass hoping to see some defects. I understand they are not always visible even with magnification.
Any and all advice appreciated.

E Sully · E Sully's Garage

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

fastfredracing · 10-14-2010, 05:29 AM

Thank you, thank you, thank you. That is exactly what I was looking for. This site rocks. From reading that thread, sounds like I have the exact same problem,symptoms, and my diagnosis led me there. I am hoping I can reflow this myself, this is a good customers car, and a good buddy, and he is a little short on cash in this tough economy

S ECU Repair · 10-14-2010, 05:46 AM

What Year is the Carrera and most important what's the Bosch Number on the DME label .

Porsche84 · Porsche84's Garage

Added link above to my technical info. Thanks, hope I never need it!

T77911S · 10-14-2010, 06:59 AM

dont forget the CPS.

as an electronics tech for the FAA for the past 20 yrs or so, bad solder joints are a BIG fix, at least for me. just fixed one the other day. my brother gave me a powered paint roller, cant remember if he said it worked or not, but it did not. found 2 bad joints.
i have also fixed quite a few DME/computers that way too. BMW, volvo, porsche, non are exempt. i find this more in consumer products more so than air traffic equipment though.

ischmitz · ischmitz's Garage

Cold solder joints could cause this. But it is also possible that the Darlington itself is damaged of the driver circuitry. When you re-solder make sure you don't damage the PCB. Unfortunately, the Bosch DME PCB quality is not the best.

Good luck and keep us posted with your results.

Ingo

fastfredracing · 10-14-2010, 09:47 AM

The Carrera is a 1983, Build date 07/1983. the Bosch # is 0-261-200-082 The Part # is 911.618.111.2
I am hoping to scrounge a little time later in the day to look closely at this unit under the glass. Hopefully, I can see the solder joint failures.
Thanks again for your help

fastfredracing · 10-14-2010, 10:17 AM

You guys have got me curious, so I just took a couple of minutes to look at this thing, and I see one distinct cold solder joint failure in one of the exact same places as on the above photos. Looks as if I am on to something. Without spending too much time, I can also see several other suspect joints.

dshepp806 · dshepp806's Garage

Especially look for any (over) heat-related areas (they'll be obvious). With proper test gear, one can check component integrity on any power transistor or darlingtin pair topology. Component failure aside (and back to solder integrity issues)....HEAVY magnification is your friend......in the end,..just reflow anything that looks remotely suspect,..then test it (phase one). Component failure discussions are another matter/discussion.

I can only say (as many others already have), that a reflow of key, high power points would be inorder,...step one. Heat her up and start refowing as your heart desires,..just becareful of what wattage your using and tip size for the job....don't create any unwanted solder bridges.

"Big glob" will not do the job...be carefull,..flow it and get out of there,..keeping the heat there ONLY as long as you need it.

Hope it turns out to be a simple issue with a cold joint!

Best,

Doyle

fastfredracing · 10-16-2010, 06:28 PM

WHOOMPA!!!. I was busy thurs- and fri, so I told my buddy( who owns the car) to bring a six pack up to the shop Saturday night, and we will solder up the suspect joints, and see what happens. There was only really one joint that I could actually see a fissure in , but two more looked slightly funny to me in the same area, so I got them just hot enough to make the existing solder quiver, and put one small dab of new on them.
Before I even put the boards back in the DME case, I said lets plug it in and see if we have spark. It fired instantly . Great news. This site really is full of some intelligent/ helpful people.
But the plot thickens.... When I got to the shop this evening, there was a 1987 light yellow targa left in the lot with a note, Broke down , no start, and a phone #. So after we put the DME back in,and bolted the seat back down, we had a victory beer, then decided to take a quick look at the 87. I have my buddy crank the motor, I can hear the fuel pump clearly , sounds normal, I go back pull the coil wire, no spark. Quick check with a noid lignt, shows injector pulse.. I check the neg side of the coil,and no flashing light.
Could it be? two in one week?
I will keep you posted...... Thanks again for the info/advise