VN05N removal (she's alive!)

deian · Unread post by **deian** » 30 Dec 2009, 14:12

Hi people,

Right, I got the bits from RS components this morning, so off I went to fetch the Hydractive ECU from the car, I snipped the contacts off the old VN05N and carefully soldered them all out, hopefully I haven't transfered too much heat into the resistors next to some of the connectors.

But getting the actual transistors off the 'wings' (as i call them) is another thing.

Here is a picture:

A few question, not sure if anyone has attempted this job before, but here goes. What on earth is holding the underside of the vn05n's to the board? I doubt it's thermal glue, I thought it was solder, and now i'm thinking it's not even super glue, but more like metal cement of some type.

What is the purpose of putting the back onto the 'wing', does this make some kind of earth connection with the rest of the board via copper rings that hold the 'wing' to the main board, or is it simply there for cooling purposes (doubtful as there is no heatsink of any kind).

Seriously, i've been with all sorts of tools, big screwdrivers, pliers, chisels, hammer (carefully), but nooooo the second one won't come off! I managed to get the first one off by bending it up backwards until it snapped... you can see the how burned and secure it was to the board.

Has anyone got any ideas on how to remove the other transistor and clean the bottom the plate. I am thinking to grind it down the broken transistor down with a dremel and carefully sand the gluey/cement off until it's shiny like the middle bit.

Many thanks!

Unread post by **Peter.N.** » 30 Dec 2009, 14:21

They are soldered to the PCB a short application of a very hot soldering iron will remove them. The only benificial effect of the solder pad is as a heat sink and to hold them still of course, if not firmly fixed, vibration will likely fracture the connections.

Peter

deian · Unread post by **deian** » 30 Dec 2009, 14:29

ahh thats why then, my soldering iron is only 25watt so it loses heat quickly if it's on something cold for long, my dad has bigger one that.

so what is holding the transistor to the board then? it's not solder surely?

and also, how well do I need to attach the new transistors to the back, could i use thermal glue?

HDI · Unread post by **HDI** » 30 Dec 2009, 14:30

It looks like that fiberglass bracket is used as a heatsink !! You could used epoxy resin to fix the new tranny's , I think I would try to use a piece of aluminium to act as a better heatsink. Then you would have the problem of isolating it though. Or , you could attach a piece of aluminium on top of the fiberglass , then attach the tranny's to that , if space allows.

deian · Unread post by **deian** » 30 Dec 2009, 14:53

thats what i thought, but surely the fibreglass isn't a good heatsink?

i like the idea of using foil, i don't think the board carries the earth to the main board, it's just there to dissipate the heat, so i may just use thermal glue if i can finish the resin board down smoothly

HDI · Unread post by **HDI** » 30 Dec 2009, 15:22

deian wrote:thats what i thought, but surely the fibreglass isn't a good heatsink?

Totally agree , but it's surprising the lengths manufacturers deploy to reduce a price by a few pence !!

Kowalski · Unread post by **Kowalski** » 30 Dec 2009, 16:00

deian wrote:thats what i thought, but surely the fibreglass isn't a good heatsink?

Its a better heatsink than nothing.

This ECU goes inside a sealed enclosure with no airflow into or out of it, so a finned heatsink is of little benefit, the heat has to go through the PCB into the casing. If it was producing a load of heat, I'd expect it to mount onto a piece of aluminium or direct to the enclosure, which would be metal (probably aluminium).

deian · Unread post by **deian** » 30 Dec 2009, 16:16

I suppose so, at least it's away from the rest of the main board.

A good soldering iron did the job of getting it off, I suupose i don't need to worry too much about solder heat with these transistors but less is better of course.

Trickiest part is bending the legs to make sure the back of the transistor sit's nicely against the back of the wing as well having the legs come through enough the other side, they aren't very long legs tbh.

I also try to make sure i'm not creating any new un-needed contacts by soldering the new legs, that would be bad news.

Thanks for the help so far.

deian · Unread post by **deian** » 30 Dec 2009, 17:33

Finally, here is naked wing, that was all solder, how they managed to weld that on so firmly and flat is beyond me (probably a machine):

Notice the drilled holes ready for the new transistors

The legs are a proper pain to bend, they have to be exact and if they are out by 1mm the back won't bend flat onto the wing.

Job done, I know i know i know, it's not tidy...

I had to use a lot of solder to hold the backs down, they may reopen/move under heat, so I don't expect this to be a permanent fix, I just want to see if it is at all possible to make it work, if it does and for however long it holds good, I have spare VN05N's here so I can do a better job next time.

Here's the underside:

Again, soldering isn't great... at all. But it should work. While it's away getting it's memory cleared I will put new do the diodes on the car. I have a hundred here, i'll grab ten, use two, so if anyone wants some, pm me, i'll gladly send anyone a few for free in an envelope (they're only 4p each). What am I going to do with a hundred!??!?

Unread post by **CitroJim** » 30 Dec 2009, 17:47

Good work Dei!

I was going to suggest a small gas soldering iron (using it as a baby blowtorch) but the big iron worked. I've a huge 125W one for these kind of jobs...

Fingers crossed it all works now....

deian wrote:What am I going to do with a hundred!??!?

Fix fifty Hydractive Xantias or 33 and a third of an Activa!

deian · Unread post by **deian** » 30 Dec 2009, 17:59

Took me a few hours of time and shaky hands to these 'two'.

I take it it's un-likely to work without a memory clear? Or is there the slightest chance?

Will get it checked anyway just to see what the lexia says about it.

Unread post by **CitroJim** » 30 Dec 2009, 18:26

Yes, it should do something Dei, even before being reset. All will happen is for each fault logged, it will use a default value and disregard the relevant sensor input.

If nothing more, you should hear the electrovalves humming with a door open and the engine not running... That will prove basic functionality.

DickieG · Unread post by **DickieG** » 30 Dec 2009, 18:43

Well done

when I did this repair on my HDi I can't recall whether the ECU burst into life before it was cleared by the Lexia, I do however recall that the ECU had recorded every fault code possible! Since I did the repair its been working perfectly.

XantiaMan · Unread post by **XantiaMan** » 30 Dec 2009, 19:27

CitroJim wrote:
If nothing more, you should hear the electrovalves humming with a door open and the engine not running... That will prove basic functionality.

Is that a definitive test that all is well with the electrovalves? Mine still buzz, but it did throw a code for the front one, if you remember? Possible it did this because i undone the multiplug with engine running when diagnosing a noise.

deian · Unread post by **deian** » 30 Dec 2009, 19:59

I will excitedly give it a whirl tomorrow, i'll be interested to know what faults it will throw up, as richard said, probably every single one of them,

out of curiosity richard, was your job tidier than mine? or is mine tidier (doubtful), because if yours worked and the soldering was similar to mine then i have a chance don't i

will wait till the new year before sending it off to richard, i will throw in some diodes, i have plenty left so again, if anyone needs any let me know, for free of course

IF it fails I will just put some soft SX spheres on the car! Fingers x'd.