CD unit woes - help me trouble shoot

[jpnovak]

I just got my engine running two weeks ago in my project. motor is a 78 SC RoW using the correct 6 pin CD. Now I have no spark. all contacts are clean.

The unit has the normal whine to it when key is on. Prior to this, the tach output did not work. When I checked I had no output on Td pin inside the box.

The dist. is putting out a signal. I get about 2.6 V(ac) when you spin by hand. I can even read the signal inside the box at the contacts.

The signal seems to be lost between the trigger input and coil signal output.

Is there a Bosch schematic for one of these 6-pin CD boxes anywhere?

Any suggestions for additional tests? Anyway to remove the guts from the box? it seems to be epoxied in place. Its not potted.


I searched the archives and found a great amount of information from Warren on the 3-pin but none on a 6pin. I assume similar tests can be done. Can I trigger this one with a momentary switch? I suppose I can continue to use the dist out of the case.

I hope someone can help since the car is ready to be driven.

[jpnovak]

bump

[jmohn]

I may have misunderstood you, but, just a thought --- have you tested the coil?

Jerry M
'78 SC

[jpnovak]

Yep, coil works fine. I think I may have a cracked solder joint on the back of the board. I just can't get to it without disconnecting every wire on it.

[RPMClassic]

Cal Al Zim, he can check the internals of that CD box for a nominal charge and make sure that all is well. When you updated the motor....did you use your existing harness in the car, or the one that was supplied with the motor. Perhaps there is a break somewhere in the wiring that is being hideen by the rubber covering.

Kepp up the good work.

Jim

[jpnovak]

Will check Zim's. they are a few hours away.

I used the harness that came with the motor and adapted it to the 71 relay panel with the 6pin CD from the 78. I don't think there is a break in the wiring since I have full continuity between the box and the coil, box and dist. , both measured from the contacts inside the box through the connectors to the destination. I am almost 100% positive the problem lies inside the CD box.

[RPMClassic]

AL'S you man then. I think he gets $125 for a full redux.

How did your centerfill gas tank turn out? Did you modify the oil tank too?

best -

Jim

[jpnovak]

The center fill turned out great. I will try and dig up some pics. I ended up cutting the side of the engine bay and fitting the later oil tank. At the time it fit in the budget and allowed me to fit the external oil lines from my 78 donor.

I was so excited two weeks ago when i first lit the motor. Then I spent a week setting up suspension and brakes. I was ready for the first test drive but can't get the motor started.

I have been having lots of problems with my CDI and dist. I am tempted to yank the hall effectsystem, install an optical trigger and put that Crane HI6R that is sitting on my shelf. I would never have to touch it again. Then I can run the carbs on the rich side with no ill effects.

[Early_S_Man]

Jamie,

The SC distributor isn't Hall-effect ... it only has a magnetic pickup coil inside that generates the trigger waveform when the 'legs' of the spider/reluctor go by .,.. I suspect you would have a hard time finding a conversion kit to optical trigger for an SC distributor!

What condition is the green trigger coax from the distributor? If it has turned brown, it needs to be replaced!

Very unusual for SC CDI to fail unless your alternator went crazy and was putting out 16 - 20 Volts ...

If the Crane unit can use a magnetic-pickup trigger signal ... why don't you install that ignition temporarily until you get the CDI tested or fixed.

[jpnovak]

Hi Warren,

The green trigger wire is nice and green. It appears that it was replaced at some pint prior to my buying the donor.

My alt. seems to be running fine, at least when I checked with a DVM last week.

The Crane unit will accept a Hall-effect trigger input. The problem is that It is not sensitive enough for this magnetic system. Installation describes using the coil output from the CD to trigger the Crane. Not going to work since my CD is toast for the moment.

Concerning the optical trigger... I was thinking that I could remove the magnetic coil setup. The depth between the rotor and the advance weights would easily clear the Crane system. I verified last night that the optical window fits the shaft on the SC dist. Now its just a matter of fitting the bracket to one of the three mounting points from teh magnetic system. I think it would work.

What kind of waveform is from the magnetic trigger? I don't have access to a scope at home. I suppose I could just take the dist to work and spin it while looking at the ouput.

I guess I was under the impression that if the CD whines it should fire. This does not seem to be the case.

Do you have any suggestions for internal tests on the CD box. I have checked most of the resistors and they seem fine. I can't quite get to the contacts on the caps to see if they are blown. I think I am going to half to unsolder all the wires and pull the top board for testing. Is there any other way to get inside this box? I find two rivets and three screws on the outer case. I assume these hold the coils on the transformer for heatsink.

[Early_S_Man]

Jamie,

I believe 'from the bottom' is the only way to get to the internal chassis-mounted parts, and to get to the underside of the board ... you have to unsolder every wire! Those solid, 25+ year-old wires should be replaced with stranded wire, preferably Teflon-insulated. Obviously, the magnet wire from the transformer can't be replaced, but it could be tied in a bundle and 'extended' with stranded wire so the board could be taken out or laid up at a right-angle for testing.

Possible problems include the input Schmidt-trigger circuit that also drives the TD signal, shorted main cap, SCR, or HV rectifier diodes ... or a bad solder joint, as you suspect! That phenolic circuit board is old, but Bosch made them pretty sturdy!

Any possibility of pics of the board?

[jpnovak]

HMM Schmidt trigger tied into the Td circuit. I also have no output from the Td to tach as measured inside the box. I think I am starting to narrow down the problem.

I would be happy to take pics of the board if/when its apart.

Are there any similarites between the diagram for the 3-pin CD. I downloaded all of those pics from the archives last night. HMM maybe we will be the first to diagram the 6pin CD.

[Shuie]

FWIW, I just replaced the points in my car with the crane optical trigger this weekend. It's an easy install. My car has never run better since I have owned it. I know you dont have points and the trigger may not be what the problem is with your car but I figured I'd mention it.

[jpnovak]

Thats great to hear Sherman. Glad it worked out. I did the same several years ago when I first got my targa.

[Shuie]

Is there an optical trigger for your SC distributor or will it not work with the 6 pin box?

[jpnovak]

The 6pin CD has extra pins for the magnetic pickup from the dist. The question is that I can not trigger my Crane ignition with the SC dist unless I do a few mods. There are two choices. Somehow install an optical trigger in teh dist for which none are made. Second I could trigger the Crane using the output from the CD which does not work. Rock and a hardplace. If I change out the magnetic system It will no longer trigger the stock CD. This might not be a problem as I suspect the Crane HI6 might run better than my less than optimal Carb conversion given the stock internals (not for long) of the CIS 3.0

[jpnovak]

I tore into the CDI yesterday. here are some reference pics for those who want to know.

Inside box.

Back of board.


Buried components.


I found one bad Cap. I replaced it and it did not help. I will continue to work through this one.

[subdewd]

It looks like that little round thingy in the midle is bad.... just kidding
I ha zimm repair mine about 9 years ago still going strong