These units provide good energy delivery but are prone to some common design-related failures. At the time of manufacture the discharge capacitor technology used was doomed to failure with age, heat and use. Simply stated, this part will fail. Also, certain components can get damaged by surge or over-voltage events caused by faulty vehicle charging systems or accidental cable reversals when jump-starting. This typically causes a failure of some of the main power components and can fuse-open internal connections.
Servicing the components in these hand-wired units requires extensive disassembly. Defective parts are replaced with modern high-quality devices with performance ratings superior to the original parts and as a matter of policy, service always includes replacement of the discharge capacitor with a superior device that does not deteriorate with heat and use. And, service always includes mods to 'harden' these units against voltage transients and reverse voltage application.
It is not necessary to replace all components in these units. With noted exceptions, the majority of components used by BOSCH are not stressed, are high quality and generally do not require replacement.
Routine service consists of disassembly, bead-blasting and re-labelling the housing to restore original appearance, diagnosis, repair, parts replacement and upgrades as needed, and stress testing at high rpms and high temperature. An optional, additional-cost service is also offered to install a fixed rev-limit feature.