Dear Art Benstein,

Hope you're well. If a 1991-92 speedo shows changes in miles-driven - but the speedometer's needle does not move at all when the car is moving - is this proof that the root of the problem is internal to the speedometer, i.e., that the instrument cluster's flexible circuit card is not implicated?

I'm aware that 1991-2 speedometers are vulnerable to capacitor failure. What is the location on the speedometer's circuit board, of the capacitor(s), failure of which causes the speedometer not to show velocity? Can you please describe the shape and color of the failed capacitor(s)?

Thanks for your help!

Yours faithfully,

Spook

Dear Spook,

Given an odometer works but the speedometer does not the surrounding instrument cluster with its flex circuit is not implicated. The problem is confined to the gauge.

I don't subscribe to the theory that we can rely on visual clues to diagnose electrical faults, yet sometimes we can get lucky with obvious damage. In those I've examined, the capacitor electrolyte may have been the source of the caustic circuit damage, but simply replacing them would not have restored function.

Best way to identify the individual components is to use the pictures with silk screen legend and corresponding diagrams I've posted here: http://cleanflametrap.com/speedo7.html

Of course you will recognize the 93/94 unit near the end of the document as your own, and can compare it to the 91/92 to see just how different they are in design. I hope you have success, but I doubt this short answer will be much help. Again, this work wouldn't have been completed without your help, and I've received kind email from all over the world expressing appreciation for the information provided.
--
Art Benstein near Baltimore

“The single biggest problem in communication is the illusion that it has taken place.” George Bernard Shaw

Dear Art Benstein,

Hope you're well. Thank you, for the detailed reply!! Am I correct to think that capacitors can "dry-out" and so lose their effectiveness? On the speedo to which I refer, I seen no sign of leakage: the board looks as good as when it left the factory!

If a dry capacitor causes the speedo to cease to show velocity, which capacitor is that likely to be? Do you know if replacements are available? Or, are the capacitors used to build these speedos tailor-made items, for which no replacement can be had?

Thanks again for sharing your insights!!

Yours faithfully,

Spook

Hi Spook,

Dried out = leaked. Difference in being observable is in the rate of leakage.

The electrolytic caps I saw in these Yazaki speedometers appeared to me to be as generic to electronics as 16p nails were in the construction of our North American stick-built homes before the advent of pneumatic nail guns. I did read Amarin's guess that they might be high-temp caps for the automotive environment -- that's currently a hot topic (!) in the dash cam reviews, and I understand the conclusion made that maybe Yazaki should have looked to aerospace parts back in the 90's. All of the new electrolytic capacitors I have in little plastic drawers are 105C rated as were those Nichicon SR found in the 91-92 Yazaki gauges. To me, 105C is standard, not 85C.

My interpretation of your questions, for the practical end, is you want to know if you might fix the speedometer by replacing capacitors. You've read of the "capacitor plague" but aren't interested in the common approach to just replace them all. To that end, I can't help.

The caps themselves would not be my first suspects. I'd look to see the gauge "motor" windings were electrically continuous to the driving pins on the chip. Examining the schematic, I'm not able to rule out that one or more caps being replaced would suddenly bring the speed needle back to life. No experience, and no documentation on the custom chips. Sorry. If you're not in a hurry, you could get it checked out the same way you did with the 93/94 unit.

--
Art Benstein near Baltimore

"The absence of evidence is not evidence of absence"