Any ideas on this??

porscheEH! · 03-29-2008, 09:35 AM

I've taken my tach apart because it only works intermitently. I have read that changing the electrolytic capacitors is the fix. I am not sure where they are though? the one silver can shaped one looks like one but it has no markings in uF to tell me it is or not, and there is another red plastic canister on the other side with no markings. There are also 2 green flat what look like capicitors in there too. also is there 2 of these elctrolytic capcitors or just one i need to change?

I have tried many other porsche forums but none seems to know anything about this tach or what capitors to change.

It's from my 1983 944

Anyone have any ideas here?

944 boy · 03-29-2008, 10:58 AM

I can see quite a number of capacitors. The two green may be your best bet. I will dig through the manual to see if it says anything. This is the first I have heard of this fix.

onZedge · 03-29-2008, 12:14 PM

Why are you convinced it's the tach? Did you swap it out with a known working one?

HondaDustR · 03-29-2008, 01:28 PM

The round silver can-shaped part in the two top photos is definitely an electrolytic capacitor. I'm about 99% sure the dark red can is also an electrolytic cap.

There are a few other types of capacitors on there as well, but those two are the only electrolytic parts I can see. If you do replace them, be sure to get the polarity right, or you'll have an in-dash explosion.

porscheEH! · 03-29-2008, 01:49 PM

I know it's the Tach because when i tap on the dash it starts working again for a while. I checked all connections and cleaned plug wires at back of tach. Also probed for voltages and signal with a multimeter at the plug and all was OK.

If your absolutely sure those cans are them then I'll replace them. I don't know where I'm going to get them from with any known markings on them. the silver one has 47/16 FRAKO written on it and a positive sign on one side for polarity and the red one has 47/16 PE EK and ROE in the middle also with polarity marked. Doesn't have voltage, tolerance or Capacitance on ether of them.

I googled the 47/16 and it came up with capacitors but there are many many different kinds of 47/16

Maybe your booK will have something about them?

944 boy · 03-29-2008, 02:38 PM

I couldn't find specifics on the early gauges themselves. Porsche's answer to a flakey gauge is to replace it. If you have or can borrow a multimeter that reads capacitance you might be able to get a reading of what it is. As for voltage and tolerance, get the highest tolerance you find that is reasonable and same with the voltage. The best would be to read the spec sheets and match physical can size.

possibly? http://www.studiosoundelectronics.com/caps.htm

HondaDustR · 03-29-2008, 02:45 PM

Yeah, I betcha they're 47 uf/16v, which are standard specs for electrolytic caps. You could find those at any Radio Shack. Be aware that capacitor technology has come a ways since the '80s, and a 47uf/16v cap today is most likely going to be a bit smaller than those. What's there to lose? You probably can't hurt anything by not having an exact capacitor installed (they're probably just for noise filtering), and it's not going to "not work" any worse from it.

Those early electrolytic caps are very prone to drying out and malfunctioning with age.

porscheEH! · 03-29-2008, 08:31 PM

I tried to take the gauge face off but the needles don't want to come off. i'll just have to unsotter the capacitors with it on. I'll make a trip to The Source and see if they can get me some. Thanks dudes for the awsome help!

Outback Porsche · 03-29-2008, 11:52 PM

I too see lots of capacitors.

It's 100% certain that the silver can is an electrolytic, and most likely 47uF 16V. The red one is not certain. What is definite is that it's in a Bakelite case, and no longer a common component case. It's possible that it is an Al electrolytic, but it is also possible it's a Mica/Plastic Film capacitor (and more than one cap inside it - similar to a starter for a fluro light). You may get away with replacing it with an Al electrolytic.

The tin can looks to be in good shape (they distort and/or leak when they've gone bad) and the Bakelite packages are normally long life capacitors. My next step would be to take the assembly apart and reflow the solder joints.

A bad joint will give you intermittent operation - a bad cap usually won't be intermittent.

Cheers,
Jeff

porscheEH! · 03-30-2008, 07:31 AM

hmm so your saying a bad capacitor is not intermittent? Well it may have another problem then. I wish i could just buy another one, but i can't find any. Ebay hasn't shown one in a very long time. Would be just easier to buy another one that works properly.

Anyone know where i could snag a early 944 tach?

porscheEH! · 03-30-2008, 07:35 AM

i also just remebered that when it did work it somtimes would read incorrectly, i'd tap the dash and it would go back to reading correctly or stop working at all. What would cause the tach to read incorrect RPM? it could be linked to it's intermittent operation.

Buddy · 03-30-2008, 09:26 AM

What color are the numbers on the tach face?

I'm pretty sure I have both a yellow number and white number somewhere that are just taking up space.

porscheEH! · 03-30-2008, 09:31 AM

Yellow number on my early style instruments. If you'd like to part with it, would be much appreciated! You want any $$ for it? and i can pay shipping. Do you know if it works alright?

Buddy · 03-30-2008, 10:01 AM

$25 for it, plus shipping. Yes, it worked fine when removed.

Dantilla · 03-30-2008, 11:38 AM

My tach is also intermittant. I've always assumed that I have a bad ground somewhere.

The car is a race car. I know where redline is on the speedometer for when the tach decides to take a rest. I don't shift until hitting the rev limiter anyway, so I haven't looked for the bad ground yet.

Maybe I'll swap in another early tach I've got laying around here somewhere and see what happens.

porscheEH! · 03-30-2008, 01:31 PM

Shipping would be to L0K 2B0 Canada. Do you have PayPal?

Outback Porsche · 03-30-2008, 02:57 PM

Now that you have a contingency plan, in that you have the option of getting another tacho, I'd still go with pulling it apart (maybe that's why I'm an electronics technician).

It sounds like there's more than one fault;

1. It's intermittent, and
2. It reads false when working.

The reading false problem will be a bad component/s, and considering the age of the tacho, it's probably a good precaution to swap out the electrolytic cap. You won't know it's bad for sure until you measure it, but yes, they do dry out with age and change value. A tell tale sign of this is that when you have it of the board and look at it's underneath, the plastic end cap inside it will have receded a little.

And seeing that you have to pull it apart and desolder the cap to do this, I'd hit all the other solder joints at the same time.

Who knows, you may get lucky.

Cheers,
Jeff

Buddy · 03-30-2008, 04:06 PM

Quote:

Originally Posted by porscheEH!

Shipping would be to L0K 2B0 Canada. Do you have PayPal?

Yes, paypal is fine.

I'll pm you the info.

I just dug it out of storage and it's in very nice condition, plexi is good but the little black nipple on the plexi is missing. You can swap yours in if you still have it.

EDIT* I answered your Rennlist post also.

porscheEH! · 03-30-2008, 05:17 PM

I have the glass and black nipple. Hopefully yours isn't on the way out too lol there the same age lol

Buddy · 04-06-2008, 08:19 PM

pm sent.