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Old 12th February 2010, 20:15   #1
FrenchMike
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Default FBH The end of the SAGA ?

MY STORY:

I came upon this Forum 3 years ago after my in tank fuel pump broke.
I found advice here to have my pump quickly and cheaply repaired.

I too also had the strange Fuel Burning Heater (FBH) behaviour caused by the K bus.
(Which I have since disconnected.)

As a regular reader, I have noted lots of threads about FBH issues and in particular
that the PCB was reported as being non repairable.

The cold days made me inclined to study the question. I began by trying to collect information about the circuit diagram etc, (not very easy)

At first I thought the Interface IC bus was the culprit.
I ordered the genuine interface IC bus (ELMOS 10026B) from Hong-Kong,
but one month later, nothing ;they forgot to ship
Meantime, I bought the Riesler interface Bus describe by Keith Alexander .
I discovered than his Interface Bus IC was a (Melexis TH3122) similar
and more easy to get.

Next, I built up a test bench and established communication between my laptop and
the Webasto PCB.
However, there was a combustion air fan error. (running at max speed).
Tracing the PCB ‘tracks’, I discovered than the power Mosfet’driver was always
ON although the Micro bus line concerned was live .The link is in fact a SMD (surface mounted) resistor well hidden under a kind of sticky sealant (looks like meringue.)
The resistor was marked 4.75 kOhms but my multimeter showed infinite !
Strange ,I had rarely seen that before in my professional live.

Anyway, I quickly replaced it and …..everything worked …..

I opened a new thread on the forums to tell the news.

So, the only possible cause, was that the resistors were being attacked by a chemical agent from that paste (meringue).

(can you imagine how many Webastos this may have affected all over the world !!)

I would like to freely publicise this valuable information, in the true spirit of the ‘Forum’ and it’s ethos of sharing information.

Most members will be able to do the work for themselves ( or know a man that can!).
However, I can do the repair for others who don’t feel like tackling the job themselves

TOOLS NEEDED:

Low power soldering iron with thin tip correctly earthed.
Table magnifier,
Solder
SM (surface mounted) resistors 4.7 Kohm ; 47Kohm


PROCEDURE

Extract the PCB from the FBH (5 screws)

Pic 1




Remove that sticky white paste and clean the area to show the resistors.
Take a measurement of them: two 4.75 Kohm and one 47 Kohm.


Pic2




If possible, built a test bench for checking out all the parameters before fitting on car.

Pic3




Results

Pic4




Enjoy your warmer car :lol:

Mike

Last edited by Dragrad; 22nd January 2016 at 01:31..
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Old 12th February 2010, 20:27   #2
BigRuss
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Default

Great work Mike

I will look forward to having a go at the repair, mines fine at the moment (touch wood) but there's quite a few members I know that have faulty ones.

Thanks for sharing your findings.



Russ
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Old 12th February 2010, 20:31   #3
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Default

Quote:
Originally Posted by FrenchMike View Post
MY STORY:

I came upon this Forum 3 years ago after my in tank fuel pump broke.
I found advice here to have my pump quickly and cheaply repaired.

I too also had the strange Fuel Burning Heater (FBH) behaviour caused by the K bus.
(Which I have since disconnected.)

As a regular reader, I have noted lots of threads about FBH issues and in particular
that the PCB was reported as being non repairable.

The cold days made me inclined to study the question. I began by trying to collect information about the circuit diagram etc, (not very easy)

At first I thought the Interface IC bus was the culprit.
I ordered the genuine interface IC bus (ELMOS 10026B) from Hong-Kong,
but one month later, nothing ;they forgot to ship
Meantime, I bought the Riesler interface Bus describe by Keith Alexander .
I discovered than his Interface Bus IC was a (Melexis TH3122) similar
and more easy to get.

Next, I built up a test bench and established communication between my laptop and
the Webasto PCB.
However, there was a combustion air fan error. (running at max speed).
Tracing the PCB ‘tracks’, I discovered than the power Mosfet’driver was always
ON although the Micro bus line concerned was live .The link is in fact a SMD (surface mounted) resistor well hidden under a kind of sticky sealant (looks like meringue.)
The resistor was marked 4.75 kOhms but my multimeter showed infinite !
Strange ,I had rarely seen that before in my professional live.

Anyway, I quickly replaced it and …..everything worked …..

I opened a new thread on the forums to tell the news.
Some members were very interested ; and among them , ‘Simpsora’ who proposed sending me his PCB for testing and, if possible, to repair it
Guess what I found on his one? 3 resistors OPEN circuit (all located under the meringue substance)
So, the only possible cause, was that the resistors were being attacked by a chemical agent from that paste (meringue).

Anyway, the issue has finally been resolved for all of us.
(can you imagine how many Webastos this may have affected all over the world !!)

I would like to freely publicise this valuable information, in the true spirit of the ‘Forum’ and it’s ethos of sharing information.

Most members will be able to do the work for themselves ( or know a man that can!).
However, I can do the repair for others who don’t feel like tackling the job themselves (provided there aren’t too many!)

TOOLS NEEDED:

Low power soldering iron with thin tip correctly earthed.
Table magnifier,
Solder
SM (surface mounted) resistors 4.7 Kohm ; 47Kohm


PROCEDURE

Extract the PCB from the FBH (5 screws)

Pic 1


Remove that sticky white paste and clean the area to show the resistors.
Take a measurement of them: two 4.75 Kohm and one 47 Kohm.

If open, leave them in place and solder the new ones on top of them . (more difficult for the small ones;
I soldered one end and made a thin wire bridge from the other end )

Pic2



If possible, built a test bench for checking out all the parameters before fitting on car.

Pic3



Results

Pic4



Enjoy your warmer car :lol:

Mike

PS: The ELMOS IC arrived today ; But I am happy to have won !
May I take this opportunity to thank French mike for all his work. I would also confirm that his 'how to 'is a genuine and 'solid ' fix for the PCB's . My own one is now working after 4yrs. of being redundant.
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Old 12th February 2010, 21:04   #4
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excellent work there - well done

need to check mine - it starts up but doesnt get hot so will to do some testing and see if i have chance this weekend to see what the fault is
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Old 12th February 2010, 21:09   #5
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So no Semiconductors failed then? Excellent Work Sir !
Hundreds of units must have been scrapped due to these resistors failing.

Amstrad products used to fail for the same reasons...................... The corrosive Glue
I used to repair Amstrad Satellites till 3 AM sometimes as they dropped like flies just after the Guarantee ended


BTW standard 1/4 Watt resistors with legs could probably be used if there is space.
So don't worry about trying to source the exact surface mount components
They will solder on the the SM lands.
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Last edited by Jules; 12th February 2010 at 21:13..
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Old 12th February 2010, 21:30   #6
Rufras
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Frenchmike, this is fantastic news as I found my failed FBH too big as a paperweight and hopeless as an anchor, well done!
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Old 12th February 2010, 22:33   #7
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Default great work .....

fantastic work , people like you are a credit to this site . It just shows that things can be brought back to life , i wonder how many fbh have been scrapped when all was needed was some tlc. This is what this site is all about ....... spot on....
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Old 12th February 2010, 22:44   #8
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this is a remarkable breakthrough, well done !
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Old 12th February 2010, 22:47   #9
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Excellent news Mike well done thanks for sharing the info.I can see Maplins being busy soon

Groover.
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Old 12th February 2010, 22:50   #10
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Really impressive work there, well done. A definite money saver!
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