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80 HP 912UL will not start

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2 years 10 months ago #9872 by Mark Kyle
Mark Kyle replied the topic: 80 HP 912UL will not start
Would help if I put my email address there wouldn't it


kylecom@tpg.com.au


Mark

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2 years 10 months ago #9873 by Kevin Stewart
Kevin Stewart replied the topic: 80 HP 912UL will not start
Mark & Daniel,

I have a circuit diagram that I have drawn from disassembling a faulty unit. I have done a double-sided PCB layout and a parts list. I have also found the faults in this particular unit.

It took me considerable time and effort to obtain this information and I am slightly nervous about giving this knowledge away so that others reading this forum can profit from my hard work.

That said I am happy to share with the Rotax community to allow owners to save themselves some money.

Not everyone is going to be able to repair these as some specialist skills and equipment will be required and very few will have a test fixture to verify the amplitude thresholds of the timing switch-over points and the impedance limits of the ignition disable circuit.

I do not know what the rules are regarding this type of repair. I guess they will vary from country to country. There may be liability issues for anyone repairing one of these units who cannot demonstrate that they followed some kind of process similar to the manufacturer. Even then the cost of defending any legal action would probably kill you financially.

In many ways it would be cheaper and safer just to build new units. I reckon the cost would be less than 100USD each.

I will ponder what best to do and let you know.

Kevin

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2 years 10 months ago - 2 years 10 months ago #9874 by Mark Kyle
Mark Kyle replied the topic: 80 HP 912UL will not start
Hi Kevin

We have done exactly the same thing. The difference is we are not trying to repair faulty modules. We aim to improve the unit to overspec the parts and improve the reliability of the modules. The intention was not to market them to the world but to be able to replace faulty units amongst the group of flyers we have here down under. I am fully aware of the legal responsibilities and what can happen so obviously we don't want to open that can of worms. The replacement cost of the modules here is outrageous and as you say even with upgraded components about 100 bucks to make one for yourself. A few of us have been deeply involved in the electronics game here for decades and have a lot of experience in design and manufacturing so doing layouts and getting boards made is a no brainer. I just want to check that we do have the schematic correct. The one we have done is for the non softstart version. Its funny that the softstart versions do not seem to fail infact we have been scouring australia and also overseas and don't seem to be able to find anyone with a dead one.
My rotax has the sofstart version which also has different parts installed on the engine to allow it to be used but it would be nice to make a unit that can be selected to be either non softstart or softstart versions.

Please email me direct and I can send you what we have done. The schematic is done in Eagle 6.6 format a sharing of information would help everyone I would think. We are looking at NOT mounting the units on the engine as it is not a good place for it with heat and vibration especially seeing the electrolytics in the unit are only 85 deg which I find astounding to design it like that especially where it is mounted.

Mark
Last Edit: 2 years 10 months ago by Mark Kyle. Reason: typo

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2 years 10 months ago #9875 by Mark Kyle
Mark Kyle replied the topic: 80 HP 912UL will not start
The non softstart units are made by Ducati I am told but not confirmed as there is nothing written on my modules in the aircraft that the softstart versions are made by Motorini but have not confirmed this

Mark

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2 years 10 months ago #9876 by Kevin Stewart
Kevin Stewart replied the topic: 80 HP 912UL will not start
I received information yesterday that suggests there may be a pair of faulty modules incorporating the soft start circuit.

Ironically the problem doesn't seem to be with the two electrolytics (which I suspected) but with the SMT components on the back of the board. There is an interesting mix of MELF and chip passives. The layout is very primitive and as a professional I would say not very good for a part requiring high availability.

It would be easy to upgrade some of the parts but without having access to the production test specification there would be a certain amount of work that would have to be done to determine the test limits.

I'll send you an email.

Kevin

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2 years 4 months ago - 2 years 4 months ago #11086 by Andy Fell
Andy Fell replied the topic: 80 HP 912UL will not start
Hi Guys,

I just joined this forum having read a lot about this module problem.

I have an 80hp circa 2006 and hey guess what!! Here in the UK we are suffering the same issues with modules of around this age.

So as an electronics engineer myself I thought I'd see if I could find the fix. As noted though, they're potted up and pretty much impossible to figure out without a lot of hard work..

Did you guys ever figure it out? the Carmo electronics guys in the Netherlands are cutting out the back, doing 'something' on the back of the PCB and then re-potting it... though I haven't figured out exact what it is that they do, it sounds simple! Rumour is of replacing capacitors, but I don't know how true this is. I was wondering if the main 'discharge' cap is getting weak but then it's difficult to see how they could replace this in the small amount of space available on the back.. Maybe it's just a cracked ceramic capacitor end cap...

Please share your thoughts. A group of us are quite keen to figure out a DIY fix, as Rotax seem to be ripping us off with the cost of new modules!

Thanks
Andy
Last Edit: 2 years 4 months ago by Andy Fell.

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2 years 4 months ago - 2 years 4 months ago #11088 by Kevin Stewart
Kevin Stewart replied the topic: 80 HP 912UL will not start
Sounds like it's time to share...

I think a collaborative effort is needed to resolve this expensive problem.

I have done some work already but run out of time to do any more at the moment.

Here is a link to some of the information that I have:

Rotax Ignition Module Files

If the back of the case is being opened up to replace components then it is the SMT parts mounted on the back of the board. If someone knows the location then the the photos that I took of the back of the board will show the likely candidates.

I took all of the caps off and measured them on a bridge so I know the values. I don't know the voltage ratings but the package size is a reasonable guide. The BOM contains my best guess at some of the parts. The FN indicates a Farnell Components part number.

If anyone needs any further info I have CAD files in Proteus format but I can create Gerber files for the layout if someone wants to make a new board. I have found a cheap source of the connectors if they are needed too.

De-potting the whole board is very time consuming but using something like a Dremell to cut a window in the case and then just remove the potting from that area is far more practical. The components can then be replaced and the hole repotted to finish the job. Given the nature of the repair it needs to be done by someone who has worked on SMT boards otherwise the repair will not be reliable.

I have suitable equipment at work and I am happy to replace components if someone can identify what needs to be changed. I can carry out the work for free on the understanding that the unit is to be used for test purposes only.

Kevin
Last Edit: 2 years 4 months ago by Kevin Stewart.
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2 years 4 months ago - 2 years 4 months ago #11089 by Andy Fell
Andy Fell replied the topic: 80 HP 912UL will not start
That's great, Kevin. thanks for sharing that, I see you've put a lot of effort into it!

So we know that it's possible to repair these units without removing any potting - by doing something on the back. What that is yet I don't know, but pilots here who've been using the Carmo guys in the Netherlands have been happy with the repair and reporting things are all ok.

That said, they still charge quite a lot for their secret :-) there seems to be a magic fix though.


rgds
Andy

Kevin Stewart wrote: Sounds like it's time to share...

I think a collaborative effort is needed to resolve this expensive problem.

I have done some work already but run out of time to do any more at the moment.

Here is a link to some of the information that I have:

Rotax Ignition Module Files

If the back of the case is being opened up to replace components then it is the SMT parts mounted on the back of the board. If someone knows the location then the the photos that I took of the back of the board will show the likely candidates.

I took all of the caps off and measured them on a bridge so I know the values. I don't know the voltage ratings but the package size is a reasonable guide. The BOM contains my best guess at some of the parts. The FN indicates a Farnell Components part number.

If anyone needs any further info I have CAD files in Proteus format but I can create Gerber files for the layout if someone wants to make a new board. I have found a cheap source of the connectors if they are needed too.

De-potting the whole board is very time consuming but using something like a Dremell to cut a window in the case and then just remove the potting from that area is far more practical. The components can then be replaced and the hole repotted to finish the job. Given the nature of the repair it needs to be done by someone who has worked on SMT boards otherwise the repair will not be reliable.

I have suitable equipment at work and I am happy to replace components if someone can identify what needs to be changed. I can carry out the work for free on the understanding that the unit is to be used for test purposes only.

Kevin

Last Edit: 2 years 4 months ago by Andy Fell.

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2 years 4 months ago - 2 years 4 months ago #11090 by Andy Fell
Andy Fell replied the topic: 80 HP 912UL will not start
PS. Thread on UK microlight forum here (I'm Wobblewing)

www.microlightforum.com/showthread.php?1...tails-where-replaced
Last Edit: 2 years 4 months ago by Andy Fell.

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2 years 4 months ago #11091 by Andy Fell
Andy Fell replied the topic: 80 HP 912UL will not start
I thought it might be the 47uF electrolytics, going off with the heat/vibes - maybe a ceramic cap on the back there to parallel with the pads for this component might help the trigger cct. Not sure if it's the trigger circuit not triggering, or if it's just lack of energy being delivered from the main storage cap.

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2 years 4 months ago #11092 by Mark Kyle
Mark Kyle replied the topic: 80 HP 912UL will not start
The 2uF large cap seems to die. I have found them as low as .5uf and regularly down at 1 and 1.3uF. This is the first place I would start as you cant get enough energy for the firing.
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2 years 4 months ago #11093 by Mark Kyle
Mark Kyle replied the topic: 80 HP 912UL will not start
By the way I am still trying to chase one of the new style ignition units that have the soft start option in them that have failed so I can have a look at them. There certainly seems to be no failures here in OZ that I can track down and very few if any world wide. The new Motorini version certainly seems to be bullet proof so far. I dont want to pull one from my aircraft and pull it apart to look at it...they are way too expensive here.

So again if anyone knows of the later motorini versions that someone has that is no good please contact me. kylecom@tpg.com.au

Mark

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2 years 4 months ago - 2 years 4 months ago #11095 by Andy Fell
Andy Fell replied the topic: 80 HP 912UL will not start

Mark Kyle wrote: The 2uF large cap seems to die. I have found them as low as .5uf and regularly down at 1 and 1.3uF. This is the first place I would start as you cant get enough energy for the firing.


Yeah I wondered that too. though if you wanted to add another one on the back and re-pot it to a smooth/flush finish (as they are doing at Carmo) it's tricky to see how you could get another, say 1uF@400V, cap to fit in there.

It might just be worth a try though, just to see if it works.. then worry about being able to fit it in later :-)
Last Edit: 2 years 4 months ago by Andy Fell.

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2 years 4 months ago #11096 by Andy Fell
Andy Fell replied the topic: 80 HP 912UL will not start
How about stick one of these on the back in parallel with the energy storage cap?

www.digikey.co.uk/product-detail/en/C575...45-6841-2-ND/2616427

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2 years 4 months ago #11097 by Mark Kyle
Mark Kyle replied the topic: 80 HP 912UL will not start
You could do that but the original will keep dying and will continue to lose its capacity. Not sure how those ceramics would hold up to the circuit design. The version I am looking at making will have that larger 2uF changeable so it can be easily replaced

Mark

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2 years 4 months ago - 2 years 4 months ago #11098 by Andy Fell
Andy Fell replied the topic: 80 HP 912UL will not start
Yep.. If the original is 2uF though, actually you'd only need a couple of those ceramics there. They can crack of course, but since we then know what to change, it shouldn't be such a big deal? It would certainly be a very low cost fix and get us going again.

As long as the original doesn't go short circuit, it shouldn't be an issue?
Would there be another issue with using a ceramic on the back in parallel with the big storage cap??

I would imagine if putting too much capacitance in parallel then there wouldn't be enough time to charge it up to enough volts before the trigger coil trips it (it's all working quite fast as far as I can work out from the coil arrangement in the rotax documentation)... so there'll be a sweet spot.

Boosting this storage cap makes sense, based on evidence so far of how these die in the field and the measurements you've made down to 0.5uF. Sounds like a good bet to me.



Mark Kyle wrote: You could do that but the original will keep dying and will continue to lose its capacity. Not sure how those ceramics would hold up to the circuit design. The version I am looking at making will have that larger 2uF changeable so it can be easily replaced

Mark

Last Edit: 2 years 4 months ago by Andy Fell.

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2 years 4 months ago #11106 by Andy Fell
Andy Fell replied the topic: 80 HP 912UL will not start
Have you seen any drop in capacitance for the 47uF electrolytics?

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2 years 4 months ago #11115 by Kevin Stewart
Kevin Stewart replied the topic: 80 HP 912UL will not start
The unit that I took apart had a bad solder joint on the end of one of the power resistors and the small SMT transistor on the back was faulty.

All the capacitors measured OK. When I first took it apart I convinced myself that the problem was likely to be the electrolytics but they both measured OK with a low ESR. The main 400V cap measured OK.

I exercised the trigger circuits and recorded some scope traces. I contemplated building a test fixture to run it up properly but other commitments got in the way ;-)

I would be interested to see a photo of the back of one of the units that has been repaired to see what area they were working in.

Kevin

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2 years 4 months ago #11117 by Andy Fell
Andy Fell replied the topic: 80 HP 912UL will not start
I'd imagined that the fault was common across all failed units, as is often the way... but if not, this would make things a little more complex :-)

Unfortunately I don't have a repaired one to look at. But I know that the back gets cut out, a repair is done and the back is re-potted... There is no resultant bulge in the back, so nothing big is being added.

I'm almost tempted to send mine off to find out... but it's all black potting, so would need to x-ray it.

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2 years 4 months ago #11118 by Andy Fell
Andy Fell replied the topic: 80 HP 912UL will not start
Do you know if the units supplied these days are exactly the same design? Is it an age they get to when they fail, or has the design been updated and improved the failure rate?

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