History of Bosch CDI ... toubleshooting info, parts list changes, and schematics ...

[gulf blue rsr]

S man you are a fantastic asset.

Found this thread today and have not yet read the vast detail, so this may be a silly question. but here goes.

I have several six pin units which are faulty.

Have you any suggestions for a set up for bench testing these six pin units out of the car when I have "repaired them".

What precautions do I need to take if I run the six pin unit on a bench DC power supply in order to test it?

I can think of several ways of doing it but can you suggest how I can best supply the input pulse to point 7 to test the unit as in the car, can I leave the output open do I need to fit a coil to the output end or can I load the unit with a ballast resistor?.

[ischmitz]

What precautions do I need to take if I run the six pin unit on a bench DC power supply in order to test it?

Make sure it has enough current capacity to drive the CD unit. It should be rated at 5 Amps or better. As a precaution a power supply with current limiter function is a plus when troubleshooting a faulty unit.

I can think of several ways of doing it but can you suggest how I can best supply the input pulse to point 7 to test the unit as in the car,

You can use a simple NE555 as pulse generator. The 6-pin requires a negative input pulse to trigger. Circuits can be found online. If you have access to a function generator with variable frequency output it is a plus since some units fail at different RPM.

Can I leave the output open do I need to fit a coil to the output end or can I load the unit with a ballast resistor?

If you leave the output open you will not test the final stage of the CD unit. DON'T USE A BALLAST RESISTOR. IT WILL DESTROY THE SRC. The CDI is designed to discharge the capacitor into an inductive load (the coil) You can hook up a used coil and a used spark plug on the bench. That way you can properly bench-test the unit. Be careful when working on the open box since you can seriously shock yourself on some of the life components. There are around 400V present at the SCR and capacitor.

Hope that helps,
Ingo

[Lorenfb]

"Have you any suggestions for a set up for bench testing these six pin units out of the car when I have "repaired them"."

Actually, the testing is really the 1st step prior to repairing.
If one lacks the testing knowledge, the "repairing" becomes questionable.

[jmchrist]

Just as an example, please find hereafter a picture of the test bench I am occasionally assembling (at home !) to repair 3 or 6 pin units.

Attached is also a picture of the modified plug used for the test. The modification is done for increasing the gap to about 6 mm (0.25 inch) in order to reach at the atmospheric pressure about the same disruptive voltage as in the cylinders.

I am using a pulse generator for simulating by RC derivation the output of the pickup coil for 6 pin units, and a simple square wave generator for testing 3 pin units.

About the power supply, if a battery is not used it is to be noted that, due to the highly inductive equivalent load of the internal flywheel converter, some energy is sent back into the power supply during a part of the 3 kHz cycle (I have measured up to 4 A peak !), so that it is useful to connect a large electrolytic capacitor in parallel at the output.
I use a 470 µF cap. for that purpose.

[Lorenfb]

"I am using a pulse generator for simulating by RC derivation the output of the pickup coil for 6 pin units, and a simple square wave generator for testing 3 pin units."

Actually, a simple sine input is all that's needed for the 6 pin with an added transistor switch
for the 3 pin.

Also, to avoid CDI damage or heart failure, the spark plug needs to contact the
CDI case, i.e. the coil ground terminal.

"some energy is sent back into the power supply during a part of the 3 kHz cycle (I have measured up to 4 A peak !), so that it is useful to connect a large electrolytic capacitor in parallel at the output.
I use a 470 µF cap. for that purpose."

It all depends on the output impedence of the power supply, i.e. its characterics.

[jmchrist]

Actually, a simple sine input is all that's needed for the 6 pin

This is correct for the operation of the unit, but for observing the triggering of the SCR the slope of a sinusoïdal signal is not fast enough for not to be perturbed by the interference with the 3 kHZ frequency of the converter. This interference is the source of an instability perturbing the observation with an oscilloscope of the triggering signals.
This instability disappears with a sharper input signal.

Also, to avoid CDI damage or heart failure, the spark plug needs to contact the
CDI case, i.e. the coil ground terminal.

Oh ! sure ! Did not you see the brown wire on my picture ? ;-)

It all depends on the output impedence of the power supply, i.e. its characterics.

Sorry, I disagree. This is not a question of output impedance. The ability of a power supply to accept some current back is rarely (may be never) specified and do not depend on the output impedance, which is normally specified only for current flowing in the forward direction, not in the reverse direction.

[Lorenfb]

"but for observing the triggering of the SCR the slope of a sinusoïdal signal is not fast enough for not to be perturbed by the interference with the 3 kHZ frequency of the converter. "

Do what????????

Check the signal from the distributor pickup, it's basically a sine wave with distortion,
i.e. harmonics. And what's the purpose of the Schmitt Trigger, i.e slow rising and falling
slopes while cranking. Use a higher freq sine wave.

The output capacitance of a power supply is a factor of its output impedence, i.e. the dynamic
or A.C. properties. Some junk power supplies don't have ANY output capacitors, and thus have
poor dynamic response to LOAD transients.

[ischmitz]

....time to break out the popcorn

[gulf blue rsr]

Wow I started something here.

Lets not get to het up it's only a bit of electronic kit.

To put the record straight I am a domestic TV audio engineer with a fully fitted workshop for LCD PLasma DVD and audio products, so I have the kit and well know both my limiuts and the limits of power supplies etc, I have enough info from this and other threads to sort the rig I need and that is what I asked for (thanks s man jmchrist and impmad2000 here and else where). gulf blue rsr is my son who I am helping out with the problems with cdi units.

What strikes me so far is that for the asking there is a load of information on these units and with some luck and a lot of reading I should be able to sort them but I cannot see for the life of me why these units cost so much to repair else where.

Thanks to all for your input all I need now is a supply of parts and again with the help of these threads I think will be able to souce them also.

[Lorenfb]

When all else fails, order a rebuilt unit from Pelican Parts!

[gulf blue rsr]

Nice one folks, burnt the midnight oil last night and managed to get two of the units up and running, couple of zenners and a dry joint, not easy to find but we got there.

on wards and up wards as they say.

[Early_S_Man]

Congrats to Gulf Blue RSR, Sr. on the repair!

Bad connections, to include bad solder joints, both on the printed circuit board and to the 'flea'clips where the 15 or 17 wires attach, and Faston connectors of the loose and corroded variety ... are the most common failure mode for the Bosch CDI units!

I had originally intended to confine discussions of the 6-pin units to the following thread, but it doesn't really matter to me ... dial-up users may have to suffer, though!

6-pin SC/Turbo CDI unit repair documentation

I normally use a Tektronix RG-501 Ramp Generator in a TM515 mainframe to trigger 6-pin units. The manual can be downloaded here:

http://www.bitsavers.org/pdf/tektronix/tm500/070-1352-00_RG501_Jul72.pdf

Almost any function generator, time mark generator, or pulse generator could be used to trigger the 6-pin Bosch or Permatune CDI units, but I already had the ramp generator ...

Here is a thread about a DIY CDI project that may be of interest to some out there who like the idea of a newly-constructed spare CDI unit ...

DIY CDI kit ... 1997 Silicon Chip magazine article from Oz ...

Here are a couple of new revised schematics to include all three of the lumped suppression resistors in the coil output circuit:

[HKZ Bob]

What is the load over the (R12) 15R ?

100 mA ?

bob

[Early_S_Man]

Bob,

With a nominal 14 Volt input from the alternator ... it is easily less than ~ 70 mA with T2 fully conducting.

[HKZ Bob]

Warren I have a 3pin Box which has an R4 but not a R12 & Diode D8.


What year was that?

Bob

[Early_S_Man]

Bob,

1973 was the only year I know of that still had R4.

Can you post the datasheets of the AEG SCRs here?

[Lorenfb]

The R4 resistor was used on all the late 3 pin CDIs until the 6 pin CDI
to reduce the susceptibility to input (#15) noise level, e.g. alternator,
fans, RF ignition, & etc.

[HKZ Bob]

Hello so this is a 73 CDI, the R4 is a 270R resistor.
It is placed between W1A & R5.




Regards
Bob

[HKZ Bob]

Warren

W stands for "Wicklung" which english word is winding
E stand for "Ende which is end
A stands for "Anfang" which is beginning....

Bob

[HKZ Bob]

Dear all,

it took me a long investigation for these datasheet.

I like this forum and that why I post these TxxN x00 COB M datasheets.

The rise time is 2 micro seconds
The closing time is 50 micro seconds. So the RIAs series does not meet these values.






Regards Bob