Well, there I was... Driving down the road when beep/flash/beep/bee/fl.. blank. There went the VIC. Then it came back. Then it went away.
So now it's sitting on my lab bench and I'm staring at a mechanical failure of the solder joint that holds the main voltage regulator diode on the board.
Heat cycle stress.
Now to see if I still remember how to do precision solder work. :)
Photos later.
"BAH"
Well, that seemed to work till I got about ten miles down the road and *paff* it went out again. After I stopped and the Jeep rested it came back, flickered a bit on the way home, then went out. Came back up about the time I got home.
!!!!I HATE TRANSIENT FAULTS!!!! Give me a nice smoked component any day, a blow fuse,....
Going to have to rip it apart again and go through every connection the hard way. It could be that diode was heat stressed to the point it's going into thermal failure, but usually they just let out the magic smoke.
The other option is to dump the VIC, which doesn't do more than provide a few idiot lights.
I don't know if this is still true, but a pretty smart guy once told me that electronic components including printed circuit boards are designed to be soldered once and only once. That's a pretty good looking repair but you had to apply more heat to melt the existing solder than the assembly was designed to take. This is his theory anyway.
Earle
** Posted from
Fairly accurate theory. Rework is always possible but you have to take care not only with how hot you get components but for how long you keep them that way. I use an Ungar solder station (adjustable temperature) and heat sinks to protect components. Go in there with one of those cheap wallyworld solder guns and you can easily fry things.
Tomorow I pull the VIC out again and take it apart. Right now I'm betting the same thermal stress that caused that crack also caused the diode to get overheated and I just reconnected an already nearly dead part.
Anyhoo, I've got an email in with one of the dealers I use. Betting it's a junkyard part or at least over $100.
"ouch!"
Expensive little doodad. Dealership wants $1,040 for it!
Think it's just going to have to be twitchy till I can either figure out what needs to be replaced/resoldered or run across a junkyard with a burnout/rollover I can pry one out of.
And of course it failed. Why? Because I missed another problem spot. This one was a slight discoloration in one of the via's and an adjoining trace. Looks like an overheat melted part of a trace and caused a break in the circuit. This may have happened because I fixed the primary problem. I'm sorta hoping the two aren't related as that would indicate something else. A busted part that without detailed schematics I'm simply not going to be able to diagnose. :(
p.s. for those that don't do board work, a "via" is simply a jumper between sides of the board. A hole with solder in it to connect traces from the front to the back.
One other thing I've learned from this is my eyeballs aren't as good as they once were. I used to be able to see teeny tiny things but found myself using a combination of magnifying glass and the digital zoom offered by the camera. :/
Any upstream issues? Usually when I see burned traces like that, something like a pump or sensor has failed.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
Nope, and that's what gets me with this doodad. The VIC only looks at a few things. Coolant/washer fluid level, doors being open/closed, transfer case position, and it has the service countdown and clock. First thing I thought of was a bad power/ground/fuses, but every wire and sensor checked out.
The VIC has a self-diagnostics and that passed even though it was cutting out after a few minutes of driving. That made me think it was power/ground. As it turned out, the first problem was mechanical, I could make the VIC cut out by smacking it with my hand. That turned out to be the diode (current regulator) that had a nice crack around both solder connections. Not what I expected, usually it is the heavier components that pull away.
On the plus side, the VIC was an "option" so simply disconnecting it won't hurt anything. I could even move the AC controls down and install a touch-screen GPS or TV.
On the ?bright? side I found a dealer that will sell a new one to me for $842, better than the local one that wants $1,040 plus tax.
That's a nice CMOS chip in the picture. A cheap soldering iron can have as much as 40V on the tip due to AC leakage.
On sensitive stuff, I either ground the tip to the ground prong on the outlet, or just unplug it when I actually make contact with the board and plug it back in to keep it hot afterwards. If you directly ground the tip, make sure the item is unplugged and the caps are drained.
;^)
Earle
The wires going to the t-case sender have been known to hit the exhaust on some types of Jeeps. Does yours route near the crossover pipe?
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
That would have scared the thing back into working again. However it would be usefull in fixing the odd body work.
I use an Ungar 9100 solder station and an esd work mat. As for ESD, CMOS is fairly resiliant compared to the old ECL chips that you could blow just by waving your hand over them. One of the big static producers is those solder suckers. Most ESD sensitive work uses the wick method but I use a Paladin PA1700 that can be grounded. Actually it needs a new tip, but they are almost as expensive as buying a new solder sucker. :/
They did. Had to fix that a few years back. :) But I'll crawl under and check again just to be sure.
the problem was.
If it didn't also blow the diode, you might be able to fix it by just using rosin flux, or a blob of rosin flux and some good multicore silver bearing solder, plus a heat sink [roach clip works], and an iron with enough heat capability to get in there and reflux that joint quick and get out before it can lift a solder pad or such on old gear.
Nah. And my credentials include electronics hardware design, but also former manager of manufacturing engineering. Plus somewhere and official NASA soldering training certificate. The trick is to get new flux in there. Optimally use a solder sucker and a drop of flux to melt and then use a Soldapullit or equivalent to get the old solder out. Then add good ersin or similar multicore solder. You can use that braid wick with flux, but it has more odds of unseating the circuit board lands. Then make sure you have a good mechanical joint--never use solder for something it isn't designed to do--support a mechanical attach. Then use just enough solder to flow such that the final joint has a concave--never convex--appearance. It should also be nice and shiny with no crystalization pattern.
As for your pretty smart guy, electronics vendors do retouch work all the time even in todays microcomponent, wave solder, vapor reflow and ROHS manufacturing cultures.
Not sure how hard it is to get good solder these days, since all new stuff is ROHS. Luckily I have a couple old 10 lb rolls of the stuff plus cleaner and resin.
What kinda diode is that? A Zener where you would need to match the current and voltage carefully? Or just your basic old high current diode where even if it were used for the typical 0.7 Silicon junction volt drop, you could probably replace it with a GlassAmp or similar from RatShack?
Diodes rarely half fail. They either dio or they open or they short.
Cant tell if they are burned from flux or burned from something worse. Could also be a conformal coating which tends to be a good idea for outdoor grade electronics.
No biggy to just wire a heavy hunk of solid wire thru the busted via, then lay another right along a busted land pattern if necessary.
That is a Motorola pulse width modulator probably used as a DC to DC convertor. I wouldn't expect 40 volts to hurt anything that is rated at
42 volt supply voltage.Not that a decent electronics soldering station has anywhere near that kind of leakage.
It's a Zener. Tested out and after the second round of repairs everything seems to be working again.
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