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Yamae has already confirmed that he believes that switchers are used in the ECU. The only alternative would be to run directly from the 12 VDC which is unlikely as most of the circuitry is likely to require 5 VDC regulated. Since the 12 VDC will see a wide variation such as when cranking (lower than 12 VDC when starter kicks in and weak battery) or when a load is switched off (starter or other loads disengaging). When I was designing equipment for the automotive environment the specs I had to meet was 6 VDC to 48 VDC. Why 48 VDC? It is not uncommon for wreckers to sometimes use a 48 VDC battery briefly in cold climates to start a car with a dead battery and also the voltage can briefly spike to this level when heavy loads are disconnected. The automotive environment is a tough one. You could use a series regulator but the series transistor would have to dissipate enormous power to maintain steady lower voltage to the chips and other circuitry. I have spoken with Yamae on numerous occasions about his familiarity with the Bode plot to stabilize the ECU power supplies. Of course even series regulators have to be stabilized using the Bode method. I have concluded that some kind of switcher is used in the ECU because large inductors always appear near the caps and between them and the power transistors in this ECU. I can't say what type of switcher is used without seeing the circuit diagram but it is likely a single ended forward converter operating in continuous/discontinuous mode or maybe a flyback converter both of which require an inductor in the circuit. Every power supply has ripple but stability is paramount.
Note about decoupling caps. Yes, they provide a source of power to the chip when the chip circuitry suddenly turns on. When the upstream traces which contain inductance see any change in current they spike upwards in voltage V=L di/dt. Decoupling caps provide that current so spike is minimized. There is a reason also why internal or external traces are next to the ground plane. It is because they provide a distributed source of capacitance to minimize the trace inductance. If an internal trace was found to be open you may not be able to simply use a surface wire to replace it because of the increased inductance it might provide. A missing ground connection however would create "ground bounce" such that one chip communicating with another chip would possibly see this as a signal and fail.
If you treat this system as a transmission line as is done in RF circuitry you find that reflections from the load (chip or other circuitry) are minimized. Therefore an impedance match is insured and no oscillations occur. Almost the same thing just a different way of looking at it. There are reasons also why some sensitive circuitry has its own voltage plane so as to isolate it from noisy loads. To know what the problems are requires knowledge of the schematic and the internal planes layout. Even Yamae was unable to get that from Denso so he had a very difficult time reverse engineering the fixes.
Note about decoupling caps. Yes, they provide a source of power to the chip when the chip circuitry suddenly turns on. When the upstream traces which contain inductance see any change in current they spike upwards in voltage V=L di/dt. Decoupling caps provide that current so spike is minimized. There is a reason also why internal or external traces are next to the ground plane. It is because they provide a distributed source of capacitance to minimize the trace inductance. If an internal trace was found to be open you may not be able to simply use a surface wire to replace it because of the increased inductance it might provide. A missing ground connection however would create "ground bounce" such that one chip communicating with another chip would possibly see this as a signal and fail.
If you treat this system as a transmission line as is done in RF circuitry you find that reflections from the load (chip or other circuitry) are minimized. Therefore an impedance match is insured and no oscillations occur. Almost the same thing just a different way of looking at it. There are reasons also why some sensitive circuitry has its own voltage plane so as to isolate it from noisy loads. To know what the problems are requires knowledge of the schematic and the internal planes layout. Even Yamae was unable to get that from Denso so he had a very difficult time reverse engineering the fixes.
I am not disputing what you say.
However, we don't know what frequency this system operates at (think 1990s computer technology). What we do know is that electrolytic capacitors have a complex impedance characteristic that is subject to variation and hence impossible to predict. That is why, in critical high-frequency applications, other types are specified. Indeed, it is not uncommon for an electrolytic to be found sitting in parallel with a ceramic disc or plate type.
Take a simple 3-terminal voltage regulator IC. Application circuits will show an electrolytic for smoothing, along with 0.1 or 0.22uF ceramic discs for decoupling either side. How many cheap power supplies have you known that have gone unstable, because the designer has not followed the application notes and simply fitted just one electrolytic across the regulator's input (which has then dried out or gone hi-Z)? Quite a lot, probably. But the failing was not due to decoupling with too low an ESR. Just the opposite, in fact.
And, I think that is all we're dealing with here.
However, we don't know what frequency this system operates at (think 1990s computer technology). What we do know is that electrolytic capacitors have a complex impedance characteristic that is subject to variation and hence impossible to predict. That is why, in critical high-frequency applications, other types are specified. Indeed, it is not uncommon for an electrolytic to be found sitting in parallel with a ceramic disc or plate type.
Take a simple 3-terminal voltage regulator IC. Application circuits will show an electrolytic for smoothing, along with 0.1 or 0.22uF ceramic discs for decoupling either side. How many cheap power supplies have you known that have gone unstable, because the designer has not followed the application notes and simply fitted just one electrolytic across the regulator's input (which has then dried out or gone hi-Z)? Quite a lot, probably. But the failing was not due to decoupling with too low an ESR. Just the opposite, in fact.
And, I think that is all we're dealing with here.
I think you are confusing stability with decoupling. The switcher uses the electrolytic capacitor as part of the filter to obtain the output voltage with acceptable ripple. The capacitor could be an ideal one with zero ESR from zero HZ to infinite frequency and the power supply might still be unstable without a compensating feedback network. It is more complicated than just decoupling. In a switcher the output voltage is fed back to the input of a difference amplifier where corrections are made to the output voltage for all line and load changes. If the corrections are such that they cause the output to increase when it should be decreasing you no longer have a power supply but you now have an oscillator. A feedback compensation network is incorporated in the feedback loop to insure that acceptable gain and phase margin are obtained. The clock frequencies used in the digital circuitry are generally much higher than those in the switcher no matter what vintage we are talking about. When I was designing switchers in1966 the highest frequency used then was about 100KHZ. As digital circutitry has evolved the need for ever smaller supplies have changed the need for switchers that can respond better to the higher digital clock frequencies. Even today's switchers that operate in the MHZ range cannot provide a low enough impedance at the frequencies of the digital clock frequencies hence the need for decoupling. The caps that are failing in the ECU are not just drying out but the corrosive nature of the electrolyte is getting past the seals, forming conductive paths that short out the cap, damaging the surface traces and sometimes destroying the internal planes.
Since a linear regulator contains a feedback loop to regulate the output voltage it too can become unstable even if supplying a steady load. Check out this app note for instability in a LDO: rohmfs.rohm.com/en/products/databook/applinote/ic/power/linear_regulator/linearreg_easy_stability_app-e.pdf
I think you are confusing stability with decoupling. The switcher uses the electrolytic capacitor as part of the filter to obtain the output voltage with acceptable ripple. The capacitor could be an ideal one with zero ESR from zero HZ to infinite frequency and the power supply might still be unstable without a compensating feedback network. It is more complicated than just decoupling. In a switcher the output voltage is fed back to the input of a difference amplifier where corrections are made to the output voltage for all line and load changes. If the corrections are such that they cause the output to increase when it should be decreasing you no longer have a power supply but you now have an oscillator. A feedback compensation network is incorporated in the feedback loop to insure that acceptable gain and phase margin are obtained. The clock frequencies used in the digital circuitry are generally much higher than those in the switcher no matter what vintage we are talking about. When I was designing switchers in1966 the highest frequency used then was about 100KHZ. As digital circutitry has evolved the need for ever smaller supplies have changed the need for switchers that can respond better to the higher digital clock frequencies. Even today's switchers that operate in the MHZ range cannot provide a low enough impedance at the frequencies of the digital clock frequencies hence the need for decoupling. The caps that are failing in the ECU are not just drying out but the corrosive nature of the electrolyte is getting past the seals, forming conductive paths that short out the cap, damaging the surface traces and sometimes destroying the internal planes.
Since a linear regulator contains a feedback loop to regulate the output voltage it too can become unstable even if supplying a steady load. Check out this app note for instability in a LDO: rohmfs.rohm.com/en/products/databook/applinote/ic/power/linear_regulator/linearreg_easy_stability_app-e.pdf
Thank you sir for what you have written.
I shall read and assimilate!
Best,
Rich
Last edited by VolumeToo; 11-27-19 at 01:41 PM.
Reason: Line spacing
Looking to Diagnose Possiblee EMC Before Spending $s
I am new to Club Lexus so first Hi!
I am tyring to find the correct thread for my problem and I am wodnering if this is it. I have an 1995 LS400 with 157,000km on the clock (that under 100k miles). Today it was slow to start, cranked strongly, but took a few turns more than usual. When on the road the hi-fi started to drop in and out then died. At the same time I lost engine power. The engine wold not rev, but could maintain possibly 1800rpm. Hard to tell beucase the tacho and the speedo were reading very low and irratic. It limped home at around 40kph (25mph?). It would not engage park and reverse, I had to use the manual lock. When it was limping home, all the dash warning lights would all come on intermitantly even though the engine was running. Forward gear changes appeared normal, but hard to tell at low speeds that don't engage all gears.
Once switched off the car would not re-start. Things that stopped working and won't restart, include the start motor, windows and telescopic steering motors and switches, hi-fi and air conditioning. Interior lights, remote central locking warning dash lights on key turn all work. Once you turn the key to start, there is no sound from the starter and the warning lights stay on but go dull.
I am unfamiliar with LS's electronics and am not that knowledgeable with elecornics, but this looks like mutliple system failures and not just the EMC. However, so many thigns are linked ont he LS I can't be sure which system(s).
I am tyring to find the correct thread for my problem and I am wodnering if this is it. I have an 1995 LS400 with 157,000km on the clock (that under 100k miles). Today it was slow to start, cranked strongly, but took a few turns more than usual. When on the road the hi-fi started to drop in and out then died. At the same time I lost engine power. The engine wold not rev, but could maintain possibly 1800rpm. Hard to tell beucase the tacho and the speedo were reading very low and irratic. It limped home at around 40kph (25mph?). It would not engage park and reverse, I had to use the manual lock. When it was limping home, all the dash warning lights would all come on intermitantly even though the engine was running. Forward gear changes appeared normal, but hard to tell at low speeds that don't engage all gears.
Once switched off the car would not re-start. Things that stopped working and won't restart, include the start motor, windows and telescopic steering motors and switches, hi-fi and air conditioning. Interior lights, remote central locking warning dash lights on key turn all work. Once you turn the key to start, there is no sound from the starter and the warning lights stay on but go dull.
I am unfamiliar with LS's electronics and am not that knowledgeable with elecornics, but this looks like mutliple system failures and not just the EMC. However, so many thigns are linked ont he LS I can't be sure which system(s).
Does this problem sound familair to anyone?
I would start with checking your battery. It could be weak. Turn on your headlights and hit the starter. If the lights go out or become very dim it is probably a shorted or weak cell in your battery. You could have a dead alternator and not getting any charge to your battery. If you have a voltmeter you could check the battery voltage and it should be at least 12.6 VDC. Get someone to charge the battery then if it starts OK and runs take it to an auto parts store where they can test your battery and alternator.
If OK some of the symptoms sound like a bad ECU but probably not. If your car had been running fine until you turned it off but wouldn't restart it could be the crankshaft position sensor is bad.
I am tyring to find the correct thread for my problem and I am wodnering if this is it. I have an 1995 LS400 with 157,000km on the clock (that under 100k miles). Today it was slow to start, cranked strongly, but took a few turns more than usual. When on the road the hi-fi started to drop in and out then died. At the same time I lost engine power. The engine wold not rev, but could maintain possibly 1800rpm. Hard to tell beucase the tacho and the speedo were reading very low and irratic. It limped home at around 40kph (25mph?). It would not engage park and reverse, I had to use the manual lock. When it was limping home, all the dash warning lights would all come on intermitantly even though the engine was running. Forward gear changes appeared normal, but hard to tell at low speeds that don't engage all gears.
Once switched off the car would not re-start. Things that stopped working and won't restart, include the start motor, windows and telescopic steering motors and switches, hi-fi and air conditioning. Interior lights, remote central locking warning dash lights on key turn all work. Once you turn the key to start, there is no sound from the starter and the warning lights stay on but go dull.
I am unfamiliar with LS's electronics and am not that knowledgeable with elecornics, but this looks like mutliple system failures and not just the EMC. However, so many thigns are linked ont he LS I can't be sure which system(s).
Does this problem sound familair to anyone?
Sounds like the alternator is finally dead or the alternator fuse is open. I'd simply start to check the alternator measuring the generating voltage at the battery posts after charging the battery using a battery charger.
I also will check the power steering pump to see the PSF leakage on to the alternator. This problem is quite common among old LS400 and Celsiors other than those ECU capacitors leak.
Found a multi-meter. The battery is reading 9.3 amps and when charged 12.4 volts (slightly low). I find out tommorrow if it starts. i guess if it does, the next thing on the list to check is the steering pump and if that's leaking the alternator. Hopefully it's not the ECU but that's for tommorow to figure out. Again, thanks kindly for your responses
Hey folks, just discovered my ECU has dead caps in it over in a separate thread. Quick question: The car is a 1993 LS400. The ECU is marked December 14, 1992. Do I order the 1992 or 1993 capacitor set?
Found a multi-meter. The battery is reading 9.3 amps and when charged 12.4 volts (slightly low). I find out tommorrow if it starts. i guess if it does, the next thing on the list to check is the steering pump and if that's leaking the alternator. Hopefully it's not the ECU but that's for tommorow to figure out. Again, thanks kindly for your responses
Is the 9.3 amps the charging current? The battery voltage is low; Is that voltage the value you read while on the charger? The current going to loads on the car should not be anywhere near 9.3 amps. I would disconnect the ground post cable from the battery but with the charger still connected to the battery post just to be sure. When the battery is fully charged the charge current should drop to a low value and the battery should show at least 12.6 volts. Most chargers automatically drop to a low trickle current value to keep it fully charged.
Hi Gumyguy, thanks for your reply. 9.3 Volts it what the battery measured when the car stopped and had no power to restart. 12.6 Volts was what it measured after removing the battery and charging it out of the car, I left it on trickle charge for another 12 hours the voltage came up toi 13.3V. When re-installed in the car, everything worked and the car operated well. I drove it for 6km and then, with the engine operating, I tested the volts which showed 11.5 Volts. The reading not alter with increased RPM, it also stayed the same when i turned off the engine. I am assuming I have a dead alternator, and I think the culpret is the power steering pump Next job is to get m hands drity I guess!
Alternator is bad. Get your local auto parts store to test alternator for sure. Power steering pump may be leaking pump fluid on the alternator which will cause the alternator windings to fail. Yamae has spoken so I believe him. There is also a reservoir where the PS fluid is added that sits directly over the alternator I think. Whenever the pump is activated by turning the steering wheel there is a valve that causes the engine to apply power to overcome the load placed on the engine. This valve is expensive so I replaced it with a plug and now no more leakage. There is a thread on this somewhere on the forum that details the thread size of a bolt that is put in place of the valve. I did it to my '94 about 3 years ago so the details are somewhat fuzzy in my mind. No more leakage and not a noticeable change on the engine due to eliminating this function.
I have a 94 ls400 and shes in the position where she cranks n starts but dies right away. Wont even hold the idle for .5 seconds. After replacing a few things, like the ect, the car would jump back into safe mode within a week or 2. So today i pulled out my ecu/ecm and found the connection of these 2 caps not looking like the rest and was wondering if they need to be replaced? Sorry about the terrible pics, my phone is the best camera i have. 😅
11-22-19, 12:37 PM
Switching regulators
Next job is to get m hands drity I guess!
