cars ecu has gone wrong again :(

Mosser · Post by **Mosser** » 16 Mar 2007, 14:34

Over the last few days i have covered about 400 miles, and the first 1-200 were perfect, no hesitation, no high idle and no cutting out,

But since yesterday the car has slowly been misfiring, idling high randomly, and yesterday it cut out on me comming home and wouldnt restart until i unplugged and replugged in the ecu, it ran badly on the way home and i parked it and it hasnt started since,

But!, i have now noticed that all the cmos chips on the board only have a 1.2-1.3volt feed, when these are 5volt devices, I artificially raised the 5 volt line inside the ecu with my mobile phone battery and a few bits of wire and it all sprang into life again, so now i have to find out where it gets its 5v power supply from for the chips in the ECU, and what has gone wrong to stop it working

Off i go again on my fault finding mission !!

Post by **Peter.N.** » 16 Mar 2007, 14:52

You'r a braver man than me and I was TV engineer!

Post by **CitroJim** » 16 Mar 2007, 15:03

I could do with you in my workshop Mosser

I'd think there would be a voltage regulator on the ECU PCB to supply the ICs, one of the 78XX family at a guess. They're normally pretty reliable though. More dry joints perhaps?

Can you see any electrolytic capacitors around the ECU? They are incredibly unreliable, especially in hot conditions and always worth replacing.

Best of luck again with this Mosser. Looks like you're not far off the solution

Mosser · Post by **Mosser** » 16 Mar 2007, 17:17

Lol !, I think i have more than enough work with this ECU at the moment!, but i'm not giving up now!

I really cannot figure out where it gets its 5v feed from at all, all the chips are interlinked on their Vcc pins as you would expect, and some of the logic chips with enable inputs are permanently tied to Vcc too, I assume this is so they are always on

But there is no 78xx series logic on this board, nearly all surface mount stuff

Could a TIP32B chip be used as a 5 volt regulator ?, this is its data sheet and it looks feasible to me http://www.ortodoxism.ro/datasheets/stm ... s/4137.pdf

Post by **CitroJim** » 16 Mar 2007, 17:31

It could be as the TIP32 does not look meaty enough to drive 4 injectors or the coil. Look at where the collector and emitter go and then the base. If it is a regulator, I'd expect the base to go off eventually to an op-amp acting as a differential amplifier with a zener reference on one of its imputs if it is acting a linear regulator.

The Vcc supply will be well regulated by some means because the massive voltage fluctuations from the battery would not allow a simple shunt zener set-up to work nearly well enough. I hope they have not gone really hi-tech and used a "chopper" type regulator as they ar a right pain to fault-find around.

Are you 100% sure that the microprocessor should be working at 5V Mosser? many do work at very low voltages. 3.3V is a very common sort of voltage for these devices.

Is there any chance you could take some really high-definition photos of the ECU? Both sides of board if possible. That may help identify any likely suspects.

Mosser · Post by **Mosser** » 16 Mar 2007, 18:02

There is a 3.3V and 5V version of the 68xx series microprocessors, mine is the HC version that requires a 5 volt feed to work, and tracing it round, it is directly linked to the 27c512 on pin 28 which requires a 5 volt feed as well

It does look like the TIP32 is being used as a regulator as one of its pins goes off to a huge motorola 212s74 w98 zener diode, but i cant find out any information on this diode at all

we are also bordering on my limits of understanding the power supply circuitry now as well !!, and i'm wondering if it would simply be easier for me to get an off the shelf 5v regulator and put it in circuit myself to supplement whatever in this ecu is failing ?, i have a nice meaty 12V feed comming in that i could tap off of, and there's an 80 omh resistance between 5V and GND so i am thinking its only using about 60Ma ?, so a 2 amp regulator should be more than enough for the job ?

What do you think ?

Post by **CitroJim** » 16 Mar 2007, 22:24

It has to be worth a go Mosser! I'd be tempted to isolate the 5V rail from the TIP32 and use a standard 7805 regulator on a decent heatsink to supply 5V. The standard 7805 is good for an amp with a decent heatsink and this will be more than adequate.

Before you do that though, check the TIP32 and it's associated components, especially any electrolytics that may be around it. It is a common transistor. Which of it's pins goes off to the huge zener? This zener may be acting as a "crowbar" protector. I found one reference on a google search suggesting this in an Magnetti Marelli ECU..

Hello everybody, need to replace this protection component from MM IAW ECU,
labeled 212S74 510 (pictute attached). I Think it´s an Overvoltage supressor
diode. Dou you know a comercial substitute or electrical parameters to find one
(Vbrakdown, Power disipation, etc)
[/url]

He never got an answer

. If indeed it is between collector (or emitter) and chassis (-ve) this'll be what it is and is worth a check too. If this zener is breaking down it'll drag down the 5V rail badly or, it may be doing it's job and protecting the processor because the TIP32 has failed and the 5V rail is too high. It is a chicken and egg situation now. Is it the Zener or the regulator circuit? Best way to check is to either substitute the Zener with another beefy 5.6V Zener or disconnect it and the circuitry downwind (to prevent damage to it if the voltage is high) and then measure the voltage coming out of the regulator. If it were me, I'd replace the Zener and the TIP32 plus any suspects around it and go from there.

If this does not work, or proves inconclusive, then go ahead and rig up a 7805 regulator. These overvoltage protect themselves quite well so the Zener would not be needed. Note that the 7805 must have some small value (.01uF disc ceramic) decoupling capacitors between its input and output pins and chassis to prevent it going unstable.

In testing the existing regulator, take extreme care not to let anything downwind of the 5V rail get subject to excess voltage. They don't like it up 'em and it would be a shame to kill anything at this stage.

Best of luck Mosser and keep us posted 8)

AndersDK · Post by **AndersDK** » 16 Mar 2007, 23:31

Are you familiar with the pwr transistor buffered 7805 regulator setup ?
The circuit where you sense the current into the 7805 and then opens the base-emitter on a parallel coupled transistor - over the 7805.

This would require a PNP pwr transistor :
emitter on +12V and high side of cs resistor
base on lo side of cs resistor and 7805 input
collector on 7805 output and 5V line
I'm pretty certain you'll find a 78L05 in smd housing near the TIP32B.
Note that recent generation voltage regs have come out in numerous new versions with improved parameters.
- and possibly with a dry solder pad

I agree the weird part no on the zener sounds as a gross fault crowbar protector.

Problems using a 7805 series device is their inherent overtemp shutdown property, which I dont believe is 100% upto the working temp range requirements of cars (-40 - +125).

Mosser · Post by **Mosser** » 17 Mar 2007, 00:02

Blimey !, you two have given me a lot to think about and consider now !!,

One thing i do find strange, is that i cannot find a decent power feed to the ECU ?, I'm assuming it will have a beefy 12v feed to it on one of its pins, but i simply cannot find it, the earth is double across pins 17 & 34 of the ECU connector, but there doesnt appear to be any dedicated 12v feed ?, where i thought it would be, turned out to be the evap purge circuit, and it doesnt stay live all the time, and now its got me wondering if all of these problems arent down to a supply fault into the ecu ?, if could be something silly like a broken wire inside the insulation !!, I actually tracked down and fixed just such a problem in the bloke across the road from me's car only a month ago where the engine would move on its mountings and flex the wiring loom and break the contact to the ignition, so the engine would die, then the engine would return to normal position and start up again and so on, it just kangarood down the road !!, i had most of his wiring loom out stretching and testing continuity of his wires for 2 days !! and i am now wondering if i am overlooking something really stupidly simple that i should have spotted weeks ago,

Trouble is that there are no circuit diagrams showing a dedicated 12v feed into a magnetti mareli 8P ecu that i can find, so i dont know where to look for it ?

Mosser · Post by **Mosser** » 17 Mar 2007, 00:18

Anders,

there is a transistor marked D1760 on my board with the middle pin cut, but the heatsink soldered to the board and commoned to the middle pin that leads directly from the base pin of the TIP32, and my knowledge of these circuit setups in way less than both of you two and i dont fully understand how it works,

I have done hours of searching for more info in this D1760 chip, but turned up nothing on it ?

dnsey · Post by **dnsey** » 17 Mar 2007, 08:22

2SD1760?
Difficult to be sure without more information, but seems a likely candidate.

Post by **CitroJim** » 17 Mar 2007, 08:30

Here is the data on the 2SD1760 It is common for the package to not have the 2S bit printed to save space.

http://www.rohm.com/products/databook/t ... sd1760.pdf

The middle pin is the collector and is commoned to the heatsink tab. If the tab goes to the base of the TIP32 then the 2SD1760 appears to be the driver for the TIP32. Where does the base of the 2SD1760 appear to go to?

Mosser · Post by **Mosser** » 17 Mar 2007, 09:56

The collector (centre pin) of the D1760 goes to the base (left pin) of the TIP32

The emitter (right pin) of the TIP32 goes to pin 35 of the main ECU connector, and I am thinking that this should be the ~12v input to this power supply circuit, and there is zero volts comming into the ecu on this pin ??, this is whats making me think that this isnt even an ECU problem now ?

The collector (centre pin) of the TIP32 is connected to the 5 volt input to all the chips, I couldnt see the physical connection as the tracks go under too many chips to be able to trace it, but there is zero resistance between the tip32 collector and the 5v rail

The big zener diode has its cathode (stripe side) connected to the emitter (right pin) of the TIP32, the other side goes to the ground rail on the board

We are running beyond my knowledge of power supplies now as i always used separate or potted psu's that always got replaced rather than repaired, we only dealt with the logic side and reflow work once the fault was identified, i am wishing i was more inquisitive now when i was working as Harris semiconductors now !!

Mosser · Post by **Mosser** » 17 Mar 2007, 11:13

So, it doesnt look like pin 35 of the ECU is its 12v input either, as it links directly to pins 1&9 on the multi function fuel ign relay, and it only appears to provide power to pin 35 if the ecu has grounded its ecu pin 4, and i cant see how it can do this without power coming in on pin 35 to provide 12v to the regulator circuit which in turn provides 5v to the chips to allows them to run !!, its like a chicken and egg situation !, you need 5v for the logic to operate to turn the 5v regulator circuit on !!

This isnt making any sense at the moment, and i need to go back over the circuit diagrams to find out exactly where the ecu gets its power from

Post by **philhoward** » 17 Mar 2007, 11:39

There will probably be only a small 12V feed to the ECU, as 99.9% of ECUs work by grounding the negative of any current drawing devices (like injectors, coils.etc). It is highly feasible that 12V isn't used inside the ECU at all as the logic will work at 5V. 50-60mA is about all the processing electronics need.

The "wakeup" circuit is most electronics is a most complex affair, and more like analogue that digital electronics most of the time. It is common for the supply input to go through an inrush resistor first (and probably a diode to protect against reverse connection), so it does appear that its a chicken and egg trick! Try doing a diode check between any possible 12V feed and the regulator input - It might read a little high, but that'll be the inrush resistor (if fitted). You could see a double drop if more than one diode is used!

I've had to rapidly relearn power supply circuits after taking on a new role at work (digitally controlled battery chargers) - its about 15 years since I did this at Uni and forgotten the lot! The ones i'm re-learning about use an inrush resistor to feed a "wake-up" circuit, that then energises a bypass circuit for the inrush resistor to allow the main electronics to wake up. Static measurements make no sense on these either...as it uses an opamp to generate the wake up voltage!