A different CDTi fan problem

[RayH]

Originally Posted by SD1too

You're doing a great diagnostic job Ray.

Simon

I get by with a lot of help from my friends
To paraphrase some old band

[FrenchMike]

Hi Guys,

The IC is a quadruple comparator (simply) LM 2901

Upload the datasheet and try to build up the drawing around .
It could help

Mike

[RayH]

Originally Posted by FrenchMike

Hi Guys,

The IC is a quadruple comparator (simply) LM 2901

Upload the datasheet and try to build up the drawing around .
It could help

Mike

Thanks Mike but I think I'll need to leave that bit to someone else
Quite happy to send you a non-working board when I've finished though if you are interested.

Ray

[FrenchMike]

Originally Posted by RayH

Thanks Mike but I think I'll need to leave that bit to someone else
Quite happy to send you a non-working board when I've finished though if you are interested.

Ray

No prob Ray,curious to know what component fails on these PCBs ....

Mike

[RayH]

Right then gents I think we have done it

Looked closely at the two boards this morning and, apart from the five components that were removed, I not convinced there weren't some other differences. However, I decided on the adventurous approach and removed said five components!

Tested off car tuned on AC - HIGH SPEED

Remained logical and checked relays, only one was closing now - excellent - but not the one currently wired to resistor, so they needed reversing. This is an extra bit of work for later as it involves extending that lead.
Reversed leads - slow speed.

Next step, bridge trinary, no effect at all, so joined thin grey to red/blue and retest - yes! High speed.

Final test with AC off remove connector to coolant sensor - high speed again, with fan continuing to run with ignition off until sensor re-connected.

Needs a bit or wiring tidied up and refitting but more than happy this afternoon

I'm still trying to get my head around what MAY have happened in the past as clearly some work, or at least investigation, has been done previously. One of the release tabs on the main connectors in the wing is snapped. We will probably never know.

Once again thanks for all your help.

Ray

[SD1too]

Well done Ray!

I remain rather confused about all the PCBs you've had though. Was the original, which didn't work, the 2 speed type with removed components? If so, then it looks like the problem was getting the grey wire from the trinary switch in the right place and transposing the relay contact heavy duty wires. Have I got that right?

Out of interest, which colour is now in the resistor circuit, red or grey?

Simon

[RayH]

Originally Posted by SD1too

Well done Ray!

I remain rather confused about all the PCBs you've had though. Was the original, which didn't work, the 2 speed type with removed components? If so, then it looks like the problem was getting the grey wire from the trinary switch in the right place and transposing the relay contact heavy duty wires. Have I got that right?

Out of interest, which colour is now in the resistor circuit, red or grey?

Simon

Thanks Simon

You are confused? What about me?

My original is here http://1drv.ms/1MDzEdP and this is the same as Steve's picture in post #41. Which would appear to be 3 speed with components removed but I can't say with certainty as I haven't actually seen a 3 speed PCB, although the signs are that it is.

The problem was not just reversing the red and grey wires, this had been tried following advice from Steve, but with the five "additional" components both relays were being energised together.

The thin grey wire, from the trinary, did not activate the fan in the position pictured above. I am inclined to think that it wouldn't have done so on my original board

The final, working, setup looks like the second picture in post #39 but it would not work correctly whilst those five components were in place.

I could be barking up the wrong tree, in the wrong forest even, but based on what I have seen I can imagine the following scenario.

2 speed fan introduced and PCB is modified (by component removal). The wiring loom is also modified by linking grey and red/blue.
At some point, either in production or a later attempted repair, a modified PCB is fitted to an unmodified loom.
Providing the fan grey and red are correct on the relays the only bit missing would be the trinary over pressure link.

I come along and find no fan function at all due to PCB failure and obtain a replacement. However this has not been modified so would presumably operate normally in a 3 speed setup?

The rest as they say ...........

I'm wondering if anyone else has tried to replace the PCB and ended up with peculiar results and possibly not noticed them.

Unless they tested it they would be unlikely to notice the trinary over pressure function was not working and possibly they may not be aware the fan was running at full speed with AC on. It may even have been put down to "It's working properly now, you can hear it!"

I hope that hasn't muddied the waters even more Simon

Incidentally, I have arranged with French Mike to send him the failed board. So we may hear more about this in the future.

[SD1too]

Thanks for your reply Ray. No, you haven't muddied the waters further. I think that you've come up with a very believable explanation.

Your experience is the best example yet of the folly of manufacturers pursuing technically sophisticated solutions when the traditional simpler principles would work just as well and be a whole lot more reliable. I mean, creating a PWM signal which they knew would be outside the expertise of dealers and has to be decoded by another circuit which no-one understands and is placed in a hostile environment for delicate electronics. All this just to trigger a couple of relays! It's madness. The petrol engine design achieves the same ends without the unreliability and mystery of the PWM circuit. As for splicing the trinary switched earth into the PWM input; well, that has all the hallmarks of a design bodge. What a mess!

Incidentally, I have arranged with French Mike to send him the failed board. So we may hear more about this in the future.

I hope so. The more we learn about this the better.

Simon

[RayH]

Originally Posted by SD1too

Thanks for your reply Ray. No, you haven't muddied the waters further. I think that you've come up with a very believable explanation.

Your experience is the best example yet of the folly of manufacturers pursuing technically sophisticated solutions when the traditional simpler principles would work just as well and be a whole lot more reliable. I mean, creating a PWM signal which they knew would be outside the expertise of dealers and has to be decoded by another circuit which no-one understands and is placed in a hostile environment for delicate electronics. All this just to trigger a couple of relays! It's madness. The petrol engine design achieves the same ends without the unreliability and mystery of the PWM circuit. As for splicing the trinary switched earth into the PWM input; well, that has all the hallmarks of a design bodge. What a mess!

I hope so. The more we learn about this the better.

Simon

I also wondered why it was so complicated compared to the petrol versions.
A couple of control wires to the relays and that would have been it, hey-ho as you say madness!

Once again thanks to everyone here for giving advice, and letting me bounce ideas off them.

Ray

[Jules]

The PWM PCB's are susceptible to damage when removing them from the relays.
No matter how careful and gradually they are removed from the tight fitting relay terminals odd faults can occur after refitting.

My guess is that the delicate surface mount components can get cracked or a solder joint broken.

The other theory is that one of the IC's is actually static sensitive and unless full SSD procedures are carried out, the board will be damaged just by touching it


This is why we don't recommend diesel owners change the relays until a reliable source of spare PCB's is found.

The 100 or so boards I had from Longbridge have all been used up so they are like hens teeth now.