it’s me - again. still troubleshooting my electrical issues on my 89 dodge colt (100K miles). still suspicious about the ECU.
online research indicates that these older mitsubishi ECUs are prone to going bad due to corrosion caused by leaky capacitors or transistors. so below (in my own replies) are some photos of my ECU. I’m pretty sure this one is a remanufactured one already - perhaps it’s the car’s second (i’ve had car for only 2 years). Anyway, if anyone wants to comment on it’s general appearance, that would be much appreciated. thanks…
broad view…
close up on yellow boxed area
I assume you’re highlighting the white residue. That is the result of incomplete cleaning of the flux residue from soldering operations. No problem.
Electrolytic capacitors can dry out and fail over time, they seldom outgas or “leak” unless subjected to excessive voltage ripple. Transistors are fully encapsulated in plastic and about the only failure with visible results is if you let the magic smoke out 
! wonderful - thanks for the reply. yes, I was concerned about the area with white residue.
you just introduced me to a new term, however, that has caught my eye and brings up another question.
what my ECU has been subjected to (or is the cause of???) for atleast 2 years now is periodic and brief episodes of rapid-fire opening and closing of a switch in the master relay, which is obviously quickly cycling power on and off to the ECU - atleast along one of it’s supply wires. would that qualify as potentially damaging ‘voltage ripple’ ??
I agree with TwinTurbo that the white residue is only(!) residue from sloppy de-fluxing. However, I see some really bad soldering by C106. Notice the solder blob under the capacitor, and what appears to be some flux residue. That blob looks like a cold solder joint. Notice also the two de-foiled lands to the left of there (and above C105); and the pointy blob of solder on the lead of D110 (just above the “C105” label). Looks like this board has been repaired before. If you are up to it, you could try reflowing the solder joints for C106. Check also for any other cold-looking solder joints around the apparent repairs. There is a small (miniscule?) chance that reflowing cold joints ould fix the problem.
And if you get one lead of the capacitor free, you can check it with an ohmeter. U using a high-resistance scale, with the leads connected one way (reverse polarity) you should see several ten-thousands ohms resistance. With the leads the other way (forward polarity), the resistance should initially be very low, then increase to a high value (hundreds of thousands of ohms) over a few seconds. (Two tutorial points: 1) You will probably need a “real” ohmeter, not a simple VOM. 2) You are not seeing an actual resistance; you are seeing a (useful) artifact of how an ohmeter works.)
BTW, You do seem willing to suffer a lot of aggravation to keep a 20-year-old Colt running.
“BTW, You do seem willing to suffer a lot of aggravation to keep a 20-year-old Colt running”
ha ha! I got a good and much needed laugh out of this statement - which helps relieve the frustration!
there is not only basic financial incentive for me to keep this running (i.e. I’m near broke!), but in a broader sense, when this car runs, it’s great, AND it gets 40 mpg!!! so how car companies get away with “bragging” about their production of ~30 mpg cars nowadays baffles and angers the ____ out of me!#$!!!
I do see all the things you pointed out, and I’m thinking re-soldering is a skill that’s beyond me. but definately, thank you.
No, that is not ripple.
Good eye art1966!
Now that you mention it, taking a closer look at C106 looks like it has been replaced. The replacement is not centered in the silkscreened circle and is much smaller than the diameter of the silkscreen outline for it. Someone has tack soldered a replacement, that did not fit the radial lead spacing of the original part, on top of the through holes for it. Not a careful job of soldering to say the least. It appears to be the same vintage as the other caps so I might suspect that it is either a lower capacitance part or a lower voltage rating. Both may be visible on the part and can be verified against a schematic for the board.
The two vias adjacent to the cap appear discolored. That appears to be a ground plane connection to other layer(s) of the board. The prior cap may have deposited the residue on failure and it turned color with heat/age. Also, there is a solder tail on the diode? D110 lead closest to the discolored vias. Someone was soldering next to them and touched the lead of D110. Would need a closer look in person to tell what happened there.
Notice the power semiconductor right next to the cap? It is a different color than the rest of them along the heatsink which might lead one to believe that both the semiconductor and cap were replaced. Now the question would be, which circuit do those components belong to?
C108 may have also been replaced as it is not positioned accurately and I see some brown spots on the circuit board where possibly a previous, failed cap may have leaked its electrolyte.
It is likely that the ECU is located where it will be kept reasonably cool but keep in mind that electrolytic caps have a max temp rating of 105C and it would be best to run them cooler than that.
Regarding the rapid application and removal of power, there is something called the NEMA Showering Arc test to be used on applicable electronic devices. In industrial applications, electronic devices must be hardened to resist externally induced transient voltages from parallel or controlled loads which may be inductive. The test involves inductance and in your case that may not be likely unless there is also a relay coil or other inductive load in parallel with your ECM’s power input. The designers of your board may have anticipated relatively infrequent application and removal of power to your ECM but not as you described. It could be risky to your ECM unless you can remove the cause for the rapid application and removal of power. Observing the voltage applied to and removed from the ECM with an oscilloscope would determine if there are transient voltages present if you really want to know.
PS, the year of your vehicle indicates that “Capacitor Plague” is not the problem. Google “Capacitor Plague WIKI” for more on this.
If you haven’t read the Wikipia article that Wha_Who cites http://en.wikipedia.org/wiki/Capacitor_plague you probably should. The electrolytic capacitors are probably the components most likely to fail and the article contains a useful material on identifying failed electrolytics.
I’d pay special attention to C106 which, we all agree, has been replaced. The concern would be that the replacement capacitor is not suited to automotive temperature ranges and might be slowly dying. See http://en.wikipedia.org/wiki/Electrolytic_capacitor#Reliability_and_length_of_life.
I hear the same thing about my 20-year old /89 Honda Accord . . . people tell me to move on, get smoething newer. I have a new Mazda RX-8 and I actually prefer the old Honda . . . better mpg, an honest 30 mpg . . . better ride . . . more room . . . and I don’t worry about where I park it in s parking lot. New cars are trying to get to 30 mpg, I’m there and the car has been paid for 17 years ago. Rocketman
The last reliable thing Mitsubishi made was the Japanese Zero. If you like torture, just pick up a Yugo. It gets better mileage than the Colt when it’s running and it’s easier to push when it isn’t!
This looks as if it was a rebuilt unit. Many times when replacing components on double sided PC boards, the old leads are cut and the new components are soldered to the leads. This is because the copper paths might lift off or be damaged if you try to desolder the old components. Also, many boards were covered in a clear sealer to help prevent corrosion. You would have to clean this off in order to desolder. Either you have a good ECU that has been rebuilt or it may be time to take a chance on another ECU from the junkyard or eBay.
I respectfully disagree. I had an '84 Mitsu Colt with the twin stick manual tranny and it got over 40 mpg all the time, sometimes 50. Tiny engine, multiple valve, 8 speed transmission with almost no weight to the car, it still was a four door which seated four adults Ok, or two adults and three kids in back. Very reliable for me, never let me down. Rocketman
Here is a list of potentially applicable development tests for an electronic device. There is little that can be done with it without the required equipment but it might provide some additional insight regarding RFI/EMI resistance regarding my comments about rapid application and removal of power to the ECM.
I suppose that it is not impossible that repair caps from the “plague years” were used.
I imagine Mitsubishi had to make a car that ran eventually! I never liked them since one stumped me in the early 90’s (yeah, I can hold a grudge). A friend of mine owned it. The car had a crank but no start condition. Since they were old, I replaced the cap, rotor, wires, and plugs. Still nothing. I had a good timing belt or chain (I forgot which), good compression, good spark, and fuel entering the cylinder. The only thing I didn’t have was a running engine! Nothing. Not even a pop. It would just crank away. After 2 days, I gave up and pushed it to a local garage. They couldn’t figure it out either (that made me feel a little better). My friend ended up junking it. I always suspected the ignition module in the distributor was bad, but at over $400 from NAPA, we didn’t want to take the chance. So I don’t mean to cut down your Colt, but I guess I just don’t take defeat gracefully. :o)