Big Dave

I saw a program on (I think) the Discovery Channel that discussed why many circuit items fail. Instead of using better materials, manufacturers use tin (I think that was the material) on circuit boards. There's a phenomenon called "tin whiskers" where the tin actually grows microscopic whiskers, kind of like a guy's beard. Those whiskers eventually form a bridge and cause a short. From what I recall, scientists have done extensive testing, but still can't determine why the whiskers appear, or what can stop them. With computer chips becoming smaller and smaller, the tin strips are being placed closer together, leading to more frequent failures caused by the whiskers.

Anyone else ever heard of this? From the program, it sounded like this fail will eventually happen to all circuits that use tin.

EDIT: Just found a link that describes it a little more...LINK

John Speake

Hi Dave,
The hybrid thick film circuit thast usually fails has silver conductor tracks, deposited onto an alumina substrate. This is a very proven technology, used in military and automotive hi-rel applications.

Generally the problem appears to be failures due to static implulses. Most of the input lines from the rest of the car go into the hybrid first. So all the circuits on theire are vunerable.

Glenferd

Mine died last year with 110K kilometers on it.

Champagne

Mine died last November in the middle of nowhere in Arizona
The LH was 17 years old and car had 88,000 miles

Paul

the flyin' scotsman

As our cars age the amount of preventative maintenance grows with the LH up there as a failure that would leave one stranded. I contemplated having my LH rebuilt for several reasons; the biggest being catastrophic failure somewhere in the 'boonies' (boonies being relative dependant on where you live), the second being gas mileage, the third being idle.

With my anticipated trip across the country to SITM and back it shall be rebuilt/replaced soon.

dr bob

I have a prophylactic rebuild sitting a few feet from me, ready to go in the car as soon as I can find the time. Plan is to keep the original still-works unit as a spare, rather than end up on the side of rod in Arizona in the summer, trying to wrestle the old unit out of the footwell. Changing it takes less than 30 mins at home in the climate-controlled workshop, a lifetime at 120+ degrees in an Arizona summer afternoon.


As much as we worry about the LH as an Achilles Heel, more than a few owners still drive around with old/original coolant and fuel hoses. Failures of those things are easier to diagnose than the LH brain... Is that steam or fire under the hood? Belts too, beyond the timing belt.

I hate being stranded, by smart stuff or stupid stuff in the car. Doesn't need to be the desert either. I similarly dislike being starnded in the garage at home, although that's a much better option than the desert highway in the summer.


Maybe we need to add a category to our Road Help List that includes "Have a spare LH? (Y/N)" I did keep all the 6-year-old coolant hoses and the belts I replaced when I did the TB job last summer. If you break down on a weekend or evening within driving distance of my garage you are welcome to use any of these parts. At other times, you can take the Explorer and dash over to 928 International for new bits.

Nicole: a loaner brain is a phone call and no more than a fedex day away from wherever you are broken. It's the time stranded, the cost of the flatbed tow if your AAA has expired, a night in a motel, and eating chicken fried steak the truckstop cafe... What I love about highway breakdowns! Plus the interesting folks you get to meet!

Tom. M

1989 GT......175,000 plus miles on it now...and still on the original LH and EZK...

Later,
Tom
89GT

John Speake

If you are lucky enough to have a spare LH thait OK, and plan to put it into store on a shelf -

short the pins on the 35 way input connector together with some aluminium foil (baking foil). Having some of the inputs pins floating can cause failure. I have seen this happen in a car that had engine out for a rebuild, so it was disconnected from its wiring harness for several weeks. When reconnectred it was dead.

I have also heard the same story when just left on a shelf for a couple of years.

SharkSkin

What's an LH module?

IcemanG17

Dave
Good one!!

Mine was "replaced" after it blew from a jump start sometime around 2000-2002...I would guess 50-70K miles.....no problems since then!

BIMMERMIKE

Costs associated with rebuild unit? How expensive ?

CMW

I believe my old 89 S-4 failed about 90K

John Speake

450USD

Tails

John, you wrote "My suspicion is that the usual mode of failure is that the chips are damaged by high voltage pulses on the input lines to the LH. But there is also good evidence that mechanical shock can also kill them".

Are these suspected voltage pulses caused from what we the owners introduce with our DIY work or are the pulses due to the normal operation of the car or are they caused by variation in voltage inputs by the different loadings place on the battery as different circuits as switched on and off?

Is there something we can do to minimise these voltage pulses?

Tails 1990 928 S4 Auto.

Bill Ball

I'd have to look it up, but mine failed suddenly driving to work one day about 2-3 years ago at about 100K miles. Fortunately, the symptoms were pretty clear, and Marc from DEVEK brought a loaner over to where I was broken down. Total down time was less than an hour. Everyone should be so fortunate.