therossinator

What would be some of the concerns for opting for a larger capacitance capacitor? Could this improve performance/range? Improve longevity? Or does it have potential to damage other circuitry?

Novice

Since this related to RF, very likely the capacity is part of the inductor-capacitor network (or LC network) which the Inductance and Capacitance values results in a resonance frequency for RFor pulsing purpose.
- btw. those light blue plastic thingies with a black plastic screw in the middle, not far from the smaller capacitor, are the inductors.

(Unlikely a capacitor for filtering AC noise) ref: https://en.wikipedia.org/wiki/LC_circuit

You are better off stay with the as designed by thee electrical engineers.

Jay777

Agreed. One has to assume the original designers knew what they were doing when they spec'd the components. Not to say there aren't better choices 20 years later but without a schematic to confirm its function, the safest approach is to replace the .47uF with a part of the same type, size, voltage rating, etc. If we can confirm the cap is used for high-frequency bypass on the receiver's supply rail (as conjectured) the best choice would actually be a be a monolithic ceramic: lower ESR, ESL, non-polarized, no dielectric loss, etc. All good. It might even yield marginally better FOB range. We'll have to wait for someone to give it a try. If anyone's interested i can suggest a part.

JPS

Loren knows his stuff, and it seems he's just suggesting a better version of the same cap. I'm going with his suggestion.

s2racer

OMG...Jay777 is a genius! So my fob would lock and unlock by standing next to the driver's door and holding the button for 3-5 seconds (24 inches away). Following Jay's suggestion to replace the diodes (Jay did the soldering to ensure it being properly done), I now have a range of 25-30 feet on my initial tests. No longer will I fear being locked out in the far corner of a dark and stormy parking lot

Thanks Jay....what a great fix.

Marc

Jay777

Great news Marc! Thanks for the update!

ed devinney

Thanks very much for this info, Jay! I just did the tantalum .47µF + electrolytic 330µF repair to my Steuergerät Wgfahrsperre, and it seems to work quite nicely. Too lazy to A/B tantalum vs electrolytic .47µF, but suspect that you won't go wrong with either component type.

Important note if you go tantalum: aluminum electrolytics are marked on the (-) side, tantalums on (+), and polarity is important so don't just plug the tantulum in. The board is clearly marked for (+) once you get the old caps off.

Jay777

Ed- great news.
Back in Sept I had my Immo out working on an Immobilizer bypass so took the opportunity to take a closer look at how the . 47 cap was used, and whether or not a different value (or type) would increase range even further. Short answer: no. I evaluated aluminum electrolytic, ceramic and tantalum caps from 0.1 to 10 uF and found no repeatable difference. Turns out the cap isn’t a high frequency bypass cap as was originally suspected, but part of a low frequency filter used to smooth the demodulated bit stream (containing the FOB code) out of the RF receiver. While it’s a critical part of the signal path, virtually any cap in the world will do the job, from the cheapest electrolytic (as was used) to the best money could buy. Why they chose a cheap, thru-hole electrolytic, with known failure modes, instead of a surface mount ceramic (used elsewhere on the board) is a bit odd. It’s possible that back in the early 90’s when the Immo was designed, SMT ceramics weren’t available in values that high, I just don’t recall. At any rate, knowing now how it’s used, the best replacement is any run-of-the-mill, thru hole, 0.47 ceramic, which is what I put in mine. It will never leak or dry out and being non-polarized can’t be installed backwards.

BTW, the FOB and receiver are capable of ranges in excess of 100 ft when bench-tested outside the car under ideal conditions. Small changes in orientation, proximity to other objects, how close the FOB is held to the body, etc., changed the range dramatically - typical for 300+ MHz, low power data links.

Jay777

For those considering the mod, here's the new recommended parts list:

0.47uF Ceramic: Digikey PN 445-181161 (TDK FA26X7R1H474KNU00) Single piece price: $0.43. This is a radial lead, non-polarized, thru hole part with the same 5mm lead spacing as the original part. Install in either direction.

330uF Electrolytic: Digikey P/N493-13140 (Nichicon UBW1A331MPD1TD. Single piece price: $1.14

If you've already used the OEM-type electrolytic, don't worry, you're good for another 10 to 15 years.

ed devinney

Or maybe longer. I bought my first 993 used but near new (2 years, 7700 miles) and the remote locks *never* had the kind of range they do now.

Paseb

These parts to get better reach with the fob?

Where can i purchase them online?

Thx for the help

Jay777

The .47 is the one that will improve FOB range (assuming you're not already in the 30 to 50 ft range). The other is a "while you're in there" thing. The one immo I actually had the opportunity to measure the old ones caps from (see post #75) showed that both were severely degraded.

Parts can be purchased online here. If you have any problems getting the parts, PM me, I'll drop a few in an envelop for you.

Paseb

So 1of each per key fob?

I just have to install them and voila?

Do i need to do something to the immo?

Jay777

The parts are installed in the immo. No mods to the FOBs. It's explained at the top of the thread.

Sagres74

Although this may or may not be common knowledge, cleaning the battery terminals with some Deoxit will do wonders to extend the FOB's range.

Back story: recently noticed a serious decrease in my range. I.e. I had to be right next to my driver's door to arm or disarm the system. I opened the FOB, tested the battery showing great results, then thoroughly cleaned the terminals, including the connecting points on the PCB, with Deoxit. The results are outstanding: I can now arm and disarm from over 15ft away.