for something of this vintage, it's probably for polarity protection of either the processor, where the memory bank. The picture isn't detailed or large enough for me to trace the circuit to either area. But yeah, that thing is toast. On these old PCM boards, sometimes you can get away with replacing one component everything is OK. But I have the feeling that whatever that diode is protected is also toast.

but what the hell do I know, I don't deal with printed circuit boards when I work on electronics, if it doesn't have a turret board, a transformer that weighs about 20 pounds, and vacuum tubes, I don't touch it!

 

Like them tubes do you? I hear ya!

Grew up fixing radios and TV's in my dad's shop. You haven't lived till you've taken a hit from a charged capacitor in the plate supply circuit!

Had the pleasure of meeting this man back in the 90's.

History of the Garnet Amplifier Company - garnetamps.com - Home of the Garnet Amplifier Company

Way off topic, of course, sorry OP!

 

Oh yeah, I hear you. I've taken a hit from a filter capacitor array, I swear I saw the bright white lights for about 2 minutes after that. 500+ volts at who knows how many amps.

 

I don't think moisture got in. It is pretty dusty on the top side. I'll get some closer pics a little later. It looks to me to be a rather dramatic capacitor leak that discolored the diode.

 

 

What I thought was wet on the bottom was just the shiny surface of the coating they used.

 

I just put a computer in my 89 bronco. As far as I could find the Cardone reman computers from advance are the best deal since you can use a $40 off coupon and get free shipping..

 

I already ordered a NAPA unit. I was leery about the Cardone units since most reference about them was bad. Granted most of those posts were 5 to 7 years ago. I also got a bit of a deal with a corporate discount because of the company I work for.

 

Just out of curiosity I looked up the computer I got at advance on Napa's website then clicked on the warranty information. It seems that Napa's computers are Cardone's anyhow..
http://s7d9.scene7.com/is/content/Ge...39940pdf?$PDF$

Hope the computer solves your problem! Mine has been running well since I swapped them out.

 

Interesting pictures.

So that diode did survive. Never would have guessed from the first picture. Whatever happened there has actually burned into the circuit board. If you take a pick and scrape at the blackened areas, you would find that the circuit board material has actually carbonized. There will be significant destruction and pitting of the circuit board material.The normally insulating material becomes conductive when this happens and the whole situation cascades. If you catch it live, it looks like a tiny welder arc and it is really destructive to the circuit board. Of course, this is no longer a repairable condition, at least not with any degree of reliability.

There has to be a trigger event that starts this process. I don't think it was the nearby capacitor. The bottom was burnt, but I think that is the result of the heat generated by the circuit board burning up. The top of the can still looks flat. If you look carefully, there is a Y shaped score on the top of the capacitor. If the capacitor fails, it will heat up and the electrolyte will boil, pressurizing the capacitor. There is a vent on the bottom side and the top is designed to blow out, relieving the pressure in the event of failure. The contents of the electrolytic capacitor can be messy, but they are not conductive, so I don't think it will be the culprit. Component failure can cause circuit board traces to heat up and start this process, but you would find signs of damage extending along the traces from the damaged area. I don't see this in the pics. Sometimes, transient voltages can arc across closely spaced printed circuit connections and start this process, or a soldered connection may fail due to vibration and overheat. It looks like there is a pit near the capacitor that has a solder through eyelet in the center and that is likely where the destruction started. It's only speculation as to the cause, but I would go with the transient voltage spike. These ECU's are really well designed hardware and the fact they have lasted over 20 years already speaks to their quality, but everything has a life cycle. I'll agree that we likely will see more of these systems fail in the coming years. Hopefully it won't become a problem limiting the usefulness of our vehicles.

 

Another destruction pic. This time from the other side of the board. Looks to me like something other than the capacitor went bad.

 

Well if its a Tantalum Electrolytic capacitor, it's filled with sulphuric acid. That'd do it.

 

Here are some pics of the inside of my replacement eec. Looks like they only replaced the capacitors because that is the only place there is a disturbance in the coating that Ford put on it. It is already installed and it runs just fine. The paper in the box with the replacement ecm didn't mention the rebuilder but the warranty pdf on NAPA's website is from Cardone.

 

Rebuildable or not, that smelly hunk o'junk is worth $78, so off it goes and hopefully closes out this little saga.

 

Interesting damage. I'd say something flashed over, but that does take some voltage to make it happen... more than I'd expect to find in a PCM.

Glad you got the truck running again.