ECU ignition output transistors

[grober]

Came across some useful discussions on the replacement of ignition output transistors for engine ECU's which I posted on another forum. Might be of help to some folks on here/

There's a detailed discussion here BimmerNut.com Forums

It's a bit mixed but summarising what is said

the transistor you're looking for is an NPN Darlington with (IIRC) 20A Icmax, and something like 100-200V Vcemax

Pay attention to the characteristic "diode forward voltage" - this is the voltage that has to be overcome in order to turn transistor on. The value of 2.5V listed for these transistors is around the point at which logical "0" turns into "1" for integrated circuits. This is what we have here - a chip controls these transistors sending out logical "1" in sequential manner. Values below this voltage - say common .7 for ordinary transistors is no good, since it can be overcome by logical "0" which is not desirable.

The transistor suggested by Dieselman the BU931 would appear to fit the bill. Available here. STMICROELECTRONICS|BU931-T|DARLINGTON TRANSISTOR, TO-220 | Farnell United Kingdom
If I remember correctly the transistors are glued to their heat sink and that page also lists a suitable adhesive

the transistor spec sheet is here
http://www.st.com/stonline/products/literature/ds/1004.pdf
note the transistor is available in alternative packages but you probably need the TO-247 one

I have not tried these myself so cannot guarantee suitability or that they won't damage the rest of the ECU. So read the thread and AT YOUR OWN RISK-----------------!!!!

p.s. Don't know if this "technology" would apply to 90's cars rather than the most up to date models or not but given they are often just switching to ground ???


So if you have an old ECU with knackered output transistors and you fancy your chances with a soldering iron--------???????????

 

[Algoritmus]

Hi Grober,

I have ordered the transitors and disassembled the ECU to see how difficult to replace the transistors. I dont think it will be a big deal.

Required tools: TX10 torx, ECU

Remove the front cover of ECU, unscrew the 7 torx screw

 

[Algoritmus]

Remove transistor securing metal thingy. The transistors behind the blue panel
See the two clip on the side:

Lift up gently on the sides, use a flat screwdriver

and the other side as well

The removed metal thingy. You can see this metal thingy can hold down 3 transistor, but here we have only 2 because this ECU is for 4 cyl. engine.

And the transistors (there is room for an other one on the left)

Now you can remove the bottom cover (only after removed the metal thingy otherwise you can damage the PCB !!!!!). Undo the 9 screw...

The bottom of PCB:

and the legs of the 2 transistor. There are plenty of room to soldering :bannana:

....to be continued...

 

[Dieselman]

Any pictures?

I've not done a Mercedes ignition unit but did use the aforementioned transistor to repair a Fiat one many moons ago.

New unit £65, new transistor £3.

It's pretty well always the output transistor blows as that is doing all the heavy duty work so get hot.
Be advised to change the coils as well in case they are creating excess load.

 

[Algoritmus]

Of course I have ordered the wrong parts .....I mean the right parts but with wrong packaging....TO-220 IS WRONG. The right is as Grober mentioned is: TO-247, because the first one is too small (leg distance etc.)

But reordered the right transistors: 14 pounds....so far so good

 

[Algoritmus]

Where are the pictures ??????

 

[grober]

Where are the pictures ??????

Since this is a very interesting thread try to persevere with posting the pictures. This can be done in two ways by hosting the pictures elsewhere e.g. Flickr or a similar photo hosting site Welcome to Flickr - Photo Sharing and posting a link to them. [ there is no limit to the image file size but has to be of reasonable dimensions to fit on most folks screens] or by attaching the jpeg files to your post - explained here http://www.mbclub.co.uk/forums/howto/5722-howto-attach-pictures-post.html you should also be aware that there is a limit to the size of jpeg you can attach so you may have to use some form of image compression programme like Microsoft Office Picture Manager- [there are other free ones out there]on the original digital camera images which are typically several Mbytes.
Here is an attached image of a table of the maximum attachment file sizes. Its called attsize.jpg and its 55.4KB -well below the 227KB limit for jpg files.

 

[grober]

I should add that as Dieselman has helpfully reminded us quite frequently these ECU ignition out transistors overheat due to problems with the ignition coils or their low tension supply wiring from the ECU to the coils themselves. This is often due to thermal stress causing wiring insulation breakdown or bad connections in the ECU plug. After you repair the ECU it would be a pity if that work was wasted by the original fault causing a second failure. Have a good look at the wiring and check the coils since they are a very common failure on that engine. One coil fires 1 and 4 and the other 2 and 3 plugs. If there is evidence of coil failure replace it.

 

[Dieselman]

EDIT:

Deleting as the O/p has now sorted their picture links as well.

 

[Algoritmus]

I have uploded the pics to flickr but I am unable to insert.....

I have got a "broken sheet

" icon instead of the picture when I insert it....

 

[Algoritmus]

it is a magic.....now i can see all the pictures....

 

[Stratman]

Still not seeing the pictures here from Algoritmus, only the little red X, but I do see Grober's attsize.jpg.

 

[barry platt]

emission cleaning with wynns

Does anyone know if it is advisable to put Wynns diesel cleaner DIRECTLY into the fuel filter? If not, what are the consequences?

 

[Algoritmus]

Still not seeing the pictures here from Algoritmus, only the little red X, but I do see Grober's attsize.jpg.

ohhh crap....then I dont know....sorry....

check the pics here:

12 (640x383) | Flickr - Photo Sharing!

I have no better idea ATM

 

[grober]

ohhh crap....then I dont know....sorry....

check the pics here:

12 (640x383) | Flickr - Photo Sharing!

I have no better idea ATM

That link you posted certainly works. I guess interested forum members can follow progress that way so keep posting those pics on Flickr.

 

[Algoritmus]

I make some comments on flickr for the pics...

 

[Algoritmus]

Just a little update: the spare transistors arrived yesterday.

Today will be the big day

 

[Algoritmus]

Finally. Job done. See pictures on Flickr.http://www.flickr.com/photos/algoritmus/5570175869/ http://www.flickr.com/photos/algoritmus/sets/72157626377960796/

I am going to test it tomorrow, then update the post.

Fingers crossed.

 

[Algoritmus]

ECU is back its place.

Good news: The car is still working.
Bad news: Still no good. No improvement.

Next step will be to replace the ignition coil.

How can I access them ? Can I just unscrew the buterfly valve unit from the intake ?

Any advice is welcome.....

 

[kth286]

it is more simple than that.

I am away this weekend but I have spares galore for your to use to do diagnostic tests without having to purchase items.

if you are in a position to wait until next week you can come over and we can do some tests.