6-pin SC/Turbo CDI unit repair documentation

[NathanUK]

Silicon Controlled Rectifier.

[projects]

Holly molly, what's a wonderful world. I can rebuild this module in no time with the schematic. thanks u so much.

[wwest]

The issue of "surplus" C8 power/charge. Once the plug's spark/arc extinguishes the ignition coil's magnetic field begins to decay/collapse, voltage reverses and the coil's primary current flows around the "circle" (through the secondary of the inverter transformer) and back into C8.
So C8 ends up already partially charged when/once the inverter restarts. Note that once the SCR is fired, remains fired, the inverter transformer secondary is shorted.

[johnman001]

Which type(s) of capacitors are best for replacement?

I saw that a mylar capacitor could be used for C8, but what should be used on C1-C7?

Thanks a bunch.


John

[niner11]

This is a cross post from when my SC broke down on sunday but I thought it might be good to show how easy it is to follow Warren's post and replace a faulty CDI C8 cap. Car started on the first crank after replacement. The soldering is pretty easy so I would recommend giving it a shot if you take your time and take pictures during the whole process. Thanks to Warren and everyone else for all of the info in this thread! Chuck

I revised this post because I had to switch the C8 cap to the part from digikey listed a few posts back

[Lorenfb]

Polyproplylene?????

Maybe guess again!

Bottomline: Bring a spare CDI in the car.

[niner11]

Lorenfb, thanks for the response. Since your a D$$k 99% of the time I shouldn't expect much from
your posts. It's really pretty simple to fix again or replace with an MSD if it comes to that. Btw, your people skills suck

[rick-l]

I am not sure you are in trouble. Let me think about this for a minute but I am not sure you exceed the 150 V/uSec rise time. If you are not at 100 deg C even better.

http://www.wima.de/EN/WIMA_MKP_4.pdf

[niner11]

Thanks Rick, I can swap out the cap if need be with another suggestion that I had. Chuck

Update: I swapped out the incorrect replacement cap that I used for this more correct one.

Digi-Key - EF6155-ND (Manufacturer - ECQ-E6155KF)

[Lorenfb]

"I am not sure you exceed the 150 V/uSec rise time."

Oh, so that's the only key parameter, right?

Using the same logic: My trans in my 356 SC has an input bearing
problem. Thought I'd use an old VW trans as they are; both 4 speed,
both are trans/axel, appear to bolt-up O.K., so why not give it a try.
I don't think that I over-looked any key parameters or anything that
might be problematic, right? Maybe others on the forum might find
this info useful in solving their trans problem even though I have little
experience and knowledge in fixing/installing a trans. This solution
does seem reasonable, though.

[rick-l]

So what is the key parameter then?

[rick-l]

Originally Posted by niner11

Thanks Rick, I can swap out the cap if need be with another suggestion that I had. Chuck

Update: I swapped out the incorrect replacement cap that I used for this more correct one.

Digi-Key - EF6155-ND (Manufacturer - ECQ-E6155KF)

I am not sure that is a better part (48 V/uSec) but I am waiting for the Almighty, All Knowing Loren to supply us some useful data.

[niner11]

I hear ya. I actually PM'd him about a suitable replacement before I did anything but he would rather argue with people than simply provide a solution. Never got a response back from him.

[johnman001]

Want to see the inside of my C8? I too am trying to find a suitable replacement. I saw absolutely no markings on mine.

[popes996]

Hi there, first post, already looking for help!!

Have a '76 SC with a blown CDI and a will to repair it. I have a blown 31/1 terminal - looks to have got hot and subsequently failed. Additionally I have a burnt R2 (ouch ?!) anyone recommend a suitable replacement / outlet to supply the parts? I've looked about and can only find '10 Ohm 1/4 Watt 5%' rather than the specified '4 Watt' type - am I missing something?

All advice greatly appreciated.

[rick-l]

I talked to a capacitor manufacturers applications engineers today and described the CDI waveform and he said Metalized Polypropylene was the way to go.

WTF??

[johnman001]

Originally Posted by popes996

Hi there, first post, already looking for help!!

Have a '76 SC with a blown CDI and a will to repair it. I have a blown 31/1 terminal - looks to have got hot and subsequently failed. Additionally I have a burnt R2 (ouch ?!) anyone recommend a suitable replacement / outlet to supply the parts? I've looked about and can only find '10 Ohm 1/4 Watt 5%' rather than the specified '4 Watt' type - am I missing something?

All advice greatly appreciated.

Here is what I found:

Mouser 4 Watt, 10Ohm, Wirewound Resistor

[johnman001]

Originally Posted by rick-l

I talked to a capacitor manufacturers applications engineers today and described the CDI waveform and he said Metalized Polypropylene was the way to go.

WTF??

This is what I am going to try. I ordered mine a few days ago. I plan on inserting this into the original metal case bolted back into the stock location. I don't know if it will take the heat though..... I am assuming that BOSCH had these custom made.

Mouser Metallized Polypropylene Capacitors

[popes996]

OK, sorted the resistor issue, now I need a C1 Capacitor - Siemens 1.0mF 250 volt - rarer than rocking horse poo................?

Anyone suggest an alternative?

[gertk]

Originally Posted by popes996

OK, sorted the resistor issue, now I need a C1 Capacitor - Siemens 1.0mF 250 volt - rarer than rocking horse poo................?

Anyone suggest an alternative?

How about this one:

B32232A3105K

http://www.digikey.com/product-detail/en/B32232A3105K/495-3529-ND/1647810