Author Topic: Reverse engineering the Bosch K-Jet ignition module  (Read 23194 times)

ptashek

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #15 on: 06 July 2015, 06:39 AM »
http://gallery.w116.org/dl/42257-1/w116_im_v_DJ.ps

I do have a .sch somewhere (gEDA) but that will take forever to find.

Thanks. I'm in no rush :)
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

jimmyricket

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #16 on: 06 July 2015, 01:59 PM »
Can I just say how utterly epic this is. I'd love to help, learn where possible as I think this is a skill that classic car owners will soon be learning how to do in years to come.

ptashek

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #17 on: 07 July 2015, 05:13 AM »
Can I just say how utterly epic this is. I'd love to help, learn where possible as I think this is a skill that classic car owners will soon be learning how to do in years to come.

It will most certainly be a string of epic failures before I get something that works :)
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

markb

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #18 on: 07 July 2015, 02:00 PM »
I'm a bit of a newbie here, but I've owned a ‘79 450SEL daily-driver for 20 years or so... lucky me, my mechanic is one of my best friends. Unlucky me, he recently retired. I've always dealt with the light-weight and cosmetic stuff anyway, but now I'm having to roll up my sleeves (I did rebuild a climate control servo from spares about 15 years ago, and it still works!). I've had a nagging problem with my ignition, but I'll save that for a another post (and as we all know.. rust never sleeps!...)

Anyway, I've had a consulting business doing PCB layouts for electronics companies 30 years now (www[dot]Lumagraph[dot]net), but semi-retired lately (giving me more time to work on my 450.. and my old house!). At the cost of these units.. and what you've accomplished so far.. are you considering creating a replacement PCB? If so, if you need any help with the schematic and/or layout, I'd be glad to do it (although you probably have it under control.. and why would you want to hand off the fun part?! ;-) ). Would there be any copyright issues? Just asking!

I have a CadStar workstation, a CAD system that was grandfathered by the UK based Racal-Redac system, and still written and supported out of Bristol UK. As an aside, they have a freeware version called CadStar Express which is limited to 300 pins/50 components, which this design looks to be within. I don't know much about the gEDA system, but CadStar can handle everything from schematic to layout to bom/assembly. Of course, sourcing parts and prototyping.. and getting it to work are the bigger unknowns. Anybody want to tackle that cruise control amp :-o...?

I'm not an electrical engineer, but have done a lot of PCB layouts, and occasionally deal with fabrication and assembly subs. It looks like you and Djenka have done a lot of the hard (preliminary) work. I've gotta say, you're brave souls.. and better judges of what it would take to make this work. My analog hat's off to you.
Mark
1979 450SEL. 209k, 20+ year daily driver.
1969 Citroen DS21 Wagon. Long ago and far away, but still amazed.
1956 MGA. Dismantled 1984. Saving for my first born son (nyd!).

djenka018

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #19 on: 11 July 2015, 06:35 PM »
There's no need to reengineer these.
When they fail your engine stops and hardly any further damage to the pcb. Maybe it is.a good idea to get one or two spare even if they are faulty.
In my experience, hardly anything fails past the main switching transistor and it used to be a very common component in SMPS for tv's during crt era (i think it was BU326). I've repaired perhaps 20 of these and usual culprit was deteriorating heat sink compound leading into overheating.

Bottom line plenty a options with modern variants if originality is not an issue
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ptashek

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #20 on: 11 July 2015, 08:03 PM »
I've finally put the schematic together with current component equivalents, and have ran a few simulations. Well, we have spark gents:

(higher res after click)


This is simulated spark at ~780rpm (13Hz).
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

djenka018

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #21 on: 11 July 2015, 09:25 PM »
Have a look at this link, you may find something inspiring (or totally boring):

http://www.angelfire.com/ia/lfb/Pgbosch.html

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markb

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #22 on: 12 July 2015, 07:43 AM »
Good to know there are options available. I had checked some years ago and didn't see any alternatives to the oem box at $$$+. Maybe I didn't look hard enough, or has the internet gotten better?! ;-) What a change of pace.. seeing an expense go down instead of up!

Your info (sudden death failure mode) also suggests that the box is not my ignition problem anyway. I'm surprised tho, that some of those caps last as long as they do under pretty harsh conditions.

RE Bosch modified. OMG, be careful not to over-engineer anything.. not on a Benz! The thought of getting a DOS command line involved.. and on top of that, using an idea from Lucas, Prince of Darkness. The mulit-sparking is interesting. Dare we hope to get better gas mileage? Or just a greener car?

Wow, that simulation is cool, you've made Robert Bosch smile. What software did you use? I'm just now getting an education in ignition electronics. Is your chart for an 8 cylinder? If so, shouldn't that 780rpm be 26hz? I guess it doesn't matter since there's no assembly code in our trusty MB's!
Mark
1979 450SEL. 209k, 20+ year daily driver.
1969 Citroen DS21 Wagon. Long ago and far away, but still amazed.
1956 MGA. Dismantled 1984. Saving for my first born son (nyd!).

ptashek

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #23 on: 12 July 2015, 12:45 PM »
I've used circuitlab.com, their simulations are good enough for this circuit, but I'll be doing real-life testing before committing to a design.
For final schematics and, eventually,  PCB I'll be using Eagle CAD as that's pretty much the standard.

Some crude sums suggest there's under 30EUR in component costs in this thing. Even if you add 2-3 times that to have the PCB made professionally, and the housing machined from aluminium it still is pretty obvious that MB has lost it's mind asking close to four figures for a replacement unit. Used unit supply is healthy, and prices are OK, so for myself there's more fun and curiosity to this project than practical necessity.

Also, well spotted that the spark frequency is wrong. It should be 52Hz at 780rpm for a four-stroke, single-coil V8.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

markb

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #24 on: 12 July 2015, 02:27 PM »
Small world.. I wrote an Eagle-to-Cadstar NetLister ULP last year to do an 8000 pin design for a client. I never got around to posting it though; I had to soak my head for a few weeks after his 32 iterations, a record.

Yeah.. some of the prices are capitalism at its worst. Where's the proletariat when you need them?! Have you or anyone experienced the ProgRama rebuilds? I haven't checked the exact pn, but US$158 is within reach. Is it worth the risk to open up something that isn't broken (yet) to do a preventative maintenance, like renewing the heat-sinking that Djenka referred to? Or is it potted?

In other off-topics.. are you having to re-create your schematic within circuitlab to simulate? I'm guessing Eagle doesn't have a workable Spice module?

26Hz.. I guess I was simulating my ignition problems..  :o
Mark
1979 450SEL. 209k, 20+ year daily driver.
1969 Citroen DS21 Wagon. Long ago and far away, but still amazed.
1956 MGA. Dismantled 1984. Saving for my first born son (nyd!).

ptashek

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #25 on: 12 July 2015, 05:39 PM »
Yeah.. some of the prices are capitalism at its worst. Where's the proletariat when you need them?! Have you or anyone experienced the ProgRama rebuilds? I haven't checked the exact pn, but US$158 is within reach. Is it worth the risk to open up something that isn't broken (yet) to do a preventative maintenance, like renewing the heat-sinking that Djenka referred to? Or is it potted?

I've no experience with the Programa units. But if they're as reliable as their CC modules, then it's likely to be money well spent.

As for the original PCB, it's all encased in some kind of soft, translucent silicone gel. The main power transistor is bolted onto the aluminium chassis, which acts as heat-sink. There's no thermal compound between the two, or at least not in my unit.

Quote
In other off-topics.. are you having to re-create your schematic within circuitlab to simulate?
Yeah... They're being total jerks and support neither import nor export of schematics from/to Eagle (or anything other than PDF/PNG/EPS/SVG).
It's been years since I've last done anything with electronics, but one thing hasn't changed in the EDA space - everyone still has their own, proprietary format for everything.

Quote
I'm guessing Eagle doesn't have a workable Spice module?
It provides one via PCBSim (not a cheap option either).
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

ptashek

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #26 on: 14 July 2015, 05:24 PM »
Ever wondered how those things were made by Bosch?
Well, that's how: https://www.youtube.com/watch?v=Nejl46f-lfY

I've stumbled on this video while trying to get more info on that cryptic "1120008 7/32" power transistor of theirs. The video shows another type, but those ignition modules sure look like ours :)
This is the only replacement part I haven't fully identified yet, albeit there's a bunch of worthy candidates. My current favourite is the BUV21G.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

djenka018

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #27 on: 15 July 2015, 05:18 AM »
Took me a while but I found the way to recall:

It was a darlington BU323A (hence the confusion with BU326)
http://pdf1.alldatasheet.com/datasheet-pdf/view/170491/GESS/BU323.html

Modern replaacement could be:

http://www.st.com/web/en/catalog/sense_power/FM100/CL822/SC88/PF62868

More to pick your brain:
http://users.tpg.com.au/pschamb/boschrepair.html



« Last Edit: 15 July 2015, 05:44 AM by djenka018 »
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ptashek

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #28 on: 15 July 2015, 05:49 AM »
Thanks!

There's a few documents about the ignition circuit that help picking potential candidates - peak voltage at pin 16 (T5 collector) is ~100V at ~8A peak current for ~1.5ms. From my own testing I know that the base of T5 is driven at 300mA, so max forward current gain is just under 30. Switching frequency is low enough to be irrelevant.

What's interesting is the coil - apparently the original ones were 185:1, giving 18.5kV spark output. That seems pretty low.
Modern ignition setups are driven at at least 25kV, but then again they're also multi-spark.

Edit: The BU323 is still available -> http://au.element14.com/on-semiconductor/bu323zg/darlington-transistor-sot-93/dp/9555960
« Last Edit: 15 July 2015, 05:53 AM by ptashek »
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

ptashek

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Re: Reverse engineering the Bosch K-Jet ignition module
« Reply #29 on: 22 July 2015, 08:41 PM »
Here's the final revision of the schematic, with all parts as they should be, and the entire ignition circuit shown. I'll add an Eagle schematic / PCB / BOM at some point, once my prototype is verified (parts are shipping!). Simulations show this'll work as expected :)

https://www.circuitlab.com/circuit/5ag5z6/w116-ignition-control-circuit/

If you go and make a commercial gain out of this, I want 50%  ;D
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)