Bosch CD Ignition

[Todd Simpson]

The Bosch CD box on my '71 just failed and I'm looking to fix it myself. Are there schematics avialble? Anyone else done this?

Todd

[pwd72s]

If I'm not mistaken, somebody out there offers rebuilt units, so they must be repairable... I'm hoping Warren will weigh in on this. If it's electrics, he's the man! He used to work for Lucas, right Warren? (Just kidding folks...really, Warren is good on this stuff!)

[Tony911Z]

Zims (Pano and Excellence advertiser) rebuilds these. When mine failed, I opened it up and discovered that the connection between the circuit foil and the multi pin connector had failed. I bypassed the flimsy connection by soldering in a jumper wire and the repair has lasted years. John Lowe, one of Pano's tech writers was collecting info on repairing these-I've been waiting for his article to come out.

[Zendalar]

Well, my box went too. Last week I called Bosch if it would be possible to acquire some schematics for these. Well, they made it pretty clear that every "bosch" repairshop is able to fix entire ignition systems, but not insides of one component. They told me schematics are top secret stuff and therefore they are not public knowledge.

Although I have schematics for a 3-pin, but its slightly different from my own. Because Bosch said that these schemas are not public, I am not gonna say who gave me these. Lets just say that the person has very much knowledge when it comes to Porsches.

I repaired my box couple times (mis-connection failures), and now the last time the box failed on me, I decided to replace it with something new. I chose Allison/crane pointless ignition system. There are others, but this was pretty easy installation.

[Early_S_Man]

Todd,

There were six or seven different circuit boards used by Bosch over the '69 - '77 years and some slight variations in component count. But, unless the inverter (DC-to-DC-converter that converts 14 Volts to 460 Volts) transformer is defective ... it should be repairable ...

But ... the combination of a printed circuit, discrete components, and point-to-point wiring with solid wire is a bit of a challenge to troubleshoot, and quite a bit of care is needed to disassemble the unit without making an irreversible mistake! I recommend taking a bunch of pics before the unit is disassembled, and at every step along the way! Hand-tracing through a schematic in three dimensions with hidden parts ... and no pics can't be much fun!

The inverter transistor is a 2N3055, but the rest of the semiconductors are 'house-labeled' parts, so it isn't a matter of going to Radio Shack for a generic or standard part! The switching SCR (mine is an AEG Telefunken part ... but there are others in use) is a stud-mount ... which tend to be fairly expensive these days, but there is room to substitute a TO-220AB plastic-cased part if you are careful.

I recommend replacing the solid wiring with stranded Teflon wire, and using a high-quality copper or silver-bearing solder for maximum strength of all connections! The unit is subjected to heat and vibration, and like the MFI speed switch ... has a tendency to fail from the shortcomings of 35-year old manufacturing technology! It wasn't designed or built to NASA standards ... but it CAN be repaired to those standards for troublefree operation! Just consider it a piece of vintage discrete electronics equipment from the Gemini space program ... and you will have the proper perspective!

Not all (little, actually) of the information I have is in a computer ... I will send some info by email, but it might take until tomorrow or Tuesday to gather it up.

[dean]

When someone tells me I can't have something but I can pay them to fix it, I tell them to stick it where the sun don't shine. I bought an MSD