Rats! Two mistakes in as many days. Guess I'm really slipping. Sorry again, Ralf......I'm not an engineer. Try to be helpful and then go off and mislead folks into potentially dangerous situations like capacitor explosions. Reckon I'd better reconsider offering up advice here. As to the risks of governor repair, I guess I drew my conclusions from a statistically invalid sample of one--mine. Ran the darn thing for about three years with my caps in backwards. Too cheap to buy new ones so I just turned 'em around and kept going another 86,000 miles. Guess one of these days I ought to replace 'em just to avoid a breakdown somewhere and have to limp home. Good idea on the alternate types of caps--I couldn't find any other kind back then that would fit in that tiny space. Probably can now, what with everything getting smaller, so if y'all find any non-polarized cap that can be squeezed into that space, should work just fine and last a long time and you won't have to worry about installing 'em backwards :-) Regarding the risk of heat, fire, and explosion...I was never able to get more than about 15 milliamps out of that AC alternator (speed sensor) that eventually feeds those caps. Considering that the signal gets fed through the throttle position sensor and then through a full-wave bridge rectifier and a series dropping resistor before being applied across the two caps in question (with a series smoothing resistor between 'em) to smooth out the last remaining pulses riding on that mostly speed-and-throttle dependant 0-20Volt or so DC signal, there ain' much left to produce heat. For the record, that signal then gets applied to the input of both op-amp comparators which compare it to a fixed Zener- reference voltage before, in the classic Op-Amp Configured as a Comparator style, and at the appropriate shift point, the comparator removes the bias from the base of the appropriate TIP-42C pass transistor that then unsaturates, removing drive current (unfiltered, direct from the 12 v supply, and without antispiking diodes, can you believe it!!) from the associated shift solenoid, causing the transmission to shift. Whew! Sounds a bit Rube Goldbergish, eh? Today, we'd just use a PIC microprocessor and it's internal A/D converters to read vehicle speed and throttle position separately, calculate the shift points, build in a little hysteresis loop in the program to make the upshift and downshift points a couple three-or-five MPH apart (upshift/downshift points are supposed to be different and we SURE don't want the classic closed-loop servo control "chatter" at the shift points), and drive the solenoids via a couple pass transistors from the PIC's parallel I/O ports. Much simpler, truly a digital computer, could also have a programmable shift point / performance curve via the PIC's on-board serial I/O port using your laptop computer to set them wherever you want, and it would all fit in half the space of the original board leaving plenty of room for whatever filter caps and varistors would be needed to give a good, clean, safe DC supply. And look entirely stock, to boot. Wouldn't be a bad idea at that-- and you could modify the shift points when you drop in DMC's high-performance engine to take advantage of it's added HP and desirable shift point changes. Been thinking about building such a thing but I just haven't had the time. With my record of late I probably couldn't get the darn thing to work anyway. Anyway, I always figured that if those two caps ever shorted out from natural failures or from installing them backwards it would just take the speed/throttle position signal to ground through the two aforementioned resistors. Those resistors would, if my Thevenin nodal current calculations are correct, limit the maximum possible signal current (i.e., at full 114 or so MPH vehicle speed in third gear) to about half a milliamp through one cap and even less through the other. Wouldn't have guessed that a half a milliamp could cause enough heat to make anything explode, but even if it would, at sustained100+ MPH we might well deserve it. Shoot, just occurred to me, I could even measure the short circuit current at that very point by just placing a milliammeter in series with the throttle kickdown switch and jam the accelerator pedal to the floor. If you have the car at full throttle (regardless of speed), that's exactly what the kickdown microswitch is doing-- it literally shorts out the vehicle speed and throttle position signal completely at that very junction and causes the transmission to downshift. In non-Engineering terms, the Governor no longer has a signal to reference, so it just gives up, so to speak, and the car downshifts. Guess that means that if either cap ever shorts out on it's own, the car would limp home stuck in first gear. 'Course with that second resistor between the two caps, depending on which cap shorted it might just limp back shifting back and forth between first and second. Wouldn't want to drive it that way for long, might make the whole transmission explode. Now in all fairness, if those caps in question had anything to do with filtering/smoothing the car's 12VDC supply voltage, in the manner that most electrolytics are used in automobile electronics, and which a reader of the years-long Governor Computer thread would very likely assume from all the discussions about them failing from inductive kickback /counter EMF off of jump starts and the like (I suspect you assumed this too, Ralf), then I'd agree completely on the risk of shorts, heat and explosion from improperly installed capacitors. I rather suspect that the very lack of such supply filtering on the Governor's DC supply lines may well contribute the Governors checkered performance reputation, but then on the other hand the lack of such caps saves it from more consequential damage should they go and decide to short out on their own, even without the misfortune of being installed backwards. In my experience these guys tend to fail shorted when used in DC supply filtering applications-- often entirely on their own volition, without being provoked by things us humans do like installing the car battery backwards, jump starting, overcranking, and other electrical maladies. Those Siemens comparators seem remarkably tolerant of unfiltered DC supplies. Spec sheets show a wide VCC / VDD range with excellent differential balance characteristics, guess that's why. It's certainly why I've never found a drop-in replacement for 'em, but luckily (and unexpectedly) have never needed to since they don't seem to fail. Protecting us all from the consequences of component failure is, I reckon, one of the reasons they put fuses on radios and governor computers. So, my apologies for omitting details like the governor's small-signal use of these caps and indirectly causing undue alarm amongst fellow intrepid Governor experimenters. And Ralf is completely correct that if you ever do install one backwards you should discard it, not re-use it. Reverse voltage, even at low currents, will usually damage them. Farewell. Mark Hershey Sr.Director, Engineering Advanced Product Planning and Development Group Intecom, Inc. Addison, TX. ----- Original Message ----- From: "Ralf Philipp" <doc.brown@xxxx> To: <dmcnews@xxxxxxxxxxxxxxx> Sent: Wednesday, February 07, 2001 11:46 AM Subject: Re: [DML] Auto trans governor problems > > > > Possible you installed the caps backwards but the Tantalums would probably > > tolerate and work OK anyway, at least for awhile. Wouldn't likely be > > intermittent. The black rubber seals were the positive end. > > > No, no, no!!! > > If you install Tantalums backwards then they will definitely go bad. They > WILL get hot, and they might even explode. (snipped right about here, and so was this message :-)