combination meter gauges - bad caps

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combination meter gauges - bad caps

Postby rcscott » Sat Apr 05, 2008 11:18 pm

Hi everyone. I've owned a 91 gt-four rc for a bit over a year and have learned a lot from lurking on this board. I've seen a few posts recently about people with tachometer and gauge issues. I had the same problem too and fixed them, so I figured it was time to create an account here.

The problem (for me at least) was caused by blown/leaky capacitors on the circuits that drive the gauge needles. It's easy to fix and should only cost a few $ for someone that can do basic soldering.

Tachometer:
I had problems with my tach needle, most of the time it would work but sometimes it would just drop to 0. Other times, just after starting the car the needle would hover just above 0 but revving the engine hard would barely move the needle to 1k rpm. I removed the cluster from the dash and took the tach gauge out.

The picture below shows the 2 problem capacitors:

Image

You can barely see it in the picture but the terminals of the 2 circled caps look black. This was caused by electrolyte leaking out of the cap. It appears oily when wiped/scraped off with a toothpick. Both of these caps are the same, 10μF 25V 105°C. They have a polarity so make sure you remember which way they are oriented, the caps should have a line printed on one side to designate the negative terminal. When I removed these 2 caps and tested them in a multimeter they couldn't hold a charge and were clearly toast. I soldered on some new caps from Digikey (P/N P11212-ND) and my tach has been working perfectly ever since!


Boost gauge:
Everyone know the factory boost gauge on the Celica is pretty much useless because it can't display absolute values and is generally inaccurate, but it would be nice if it at least moved! This is what my boost gauge circuit looked like when I opened it up:

Image

All of that goo can't be good :wink:

The 2 caps in the image are:
22μF 25V 105°C
47μF 10V 105°C

I couldn't find ones with the same voltage rating, but as long as they are replaced with a cap with the same capacitance, a higher voltage rating shouldn't matter. Here's what I used:

22μF 35V 105°C - Digikey P/N P11230-ND
47μF 25V 105°C - Digikey P/N P10267-ND

My factory boost gauge now shows when I'm in boost or vacuum, although that's about all it can do.

Hope this helps someone, it certainly saved me $300+ on a completely new replacement cluster.
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Postby TomsGT4 » Fri Apr 11, 2008 6:47 pm

This is good, nicely done.
Tom
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Re: combination meter gauges - bad caps

Postby monkninja » Wed Feb 16, 2011 5:13 pm

holy cow! very thorough and impressive! thanks for posting this!
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Re: combination meter gauges - bad caps

Postby 2of81 » Sat Feb 26, 2011 7:56 pm

Damn I had to deal with capicator replacement in my old home stereo now in my gauge cluster!

From what I have read the average life expectancy on a capicator is 20 years.
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Re: combination meter gauges - bad caps

Postby MWP » Sun Feb 27, 2011 11:26 pm

Depends on the quality of the electrolytic capacitor, and its operating conditions.
Cap's that get hot (or are heated by nearby components), and caps that are pushed hard (near max rated voltage) wont last as long.
Also be careful with cheap Chinese caps. They can go bad very quickly.
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Re: combination meter gauges - bad caps

Postby CMS-GT4 » Sun Feb 27, 2011 11:44 pm

So does any other systems in the cluster rely on readings from the stock boost gauge? Can it be removed and not effect the rest of the cluster? I am curious if we could replace the gauge with an aftermarket one like they do in the mr2.
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Re: combination meter gauges - bad caps

Postby 2of81 » Fri Mar 11, 2011 5:32 am

MWP wrote:Depends on the quality of the electrolytic capacitor, and its operating conditions.
Cap's that get hot (or are heated by nearby components), and caps that are pushed hard (near max rated voltage) wont last as long.
Also be careful with cheap Chinese caps. They can go bad very quickly.


Yes, with vintage stereo stuff the whole thing may work with caps out of spec and bad, but it won't sound as it should. Thats what made me say something about 20 years on caps... but look at how old our cars are now.
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Re: combination meter gauges - bad caps

Postby ___Scott___ » Sun Mar 13, 2011 4:00 pm

rcscott wrote:I couldn't find ones with the same voltage rating, but as long as they are replaced with a cap with the same capacitance, a higher voltage rating shouldn't matter. Here's what I used:

22μF 35V 105°C - Digikey P/N P11230-ND
47μF 25V 105°C - Digikey P/N P10267-ND

An arguably better option is to choose ceramic caps. They don't suffer the electrolyte issues an aluminum electrolytic cap does, they are available with very good capacitance vs. temperature curves, and therefore are just more reliable.

Here is one that is a good candidate for consideration:
490-5313-1-ND, CAP CER 22UF 25V X7R 10% 1210

A little creativity may be required to mount it since it doesn't have the leads the original cap had, but it's usually pretty easy to bridge in enough solder to make it work. For the 47uF cap, you can stack two of the 22uF caps. I very strongly suspect that the total of 44uF is within the range of capacitance variation of the original aluminum electrolytic cap.

In general I avoid polar caps, both aluminum electrolytic and tantalum. I especially never use a tantalum cap in an automotive application. I've seen too many of them do a flame-thrower impression to ever spec them in anything again. Aluminum electrolytic caps sometimes offer ESR characteristics that are useful in some filter designs, but mostly I stick to ceramic caps.
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Re: combination meter gauges - bad caps

Postby monkninja » Wed May 09, 2012 12:31 pm

Well I just did this and it fixed my tachometer!!! My needle wouldn't move at all, and all it took were two 30cent capacitors!! Definitely my cheapest part replacement to date!!
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