If the diodes on an alternator die does it cause....

[cc]

The 2.5L 156 is off the road as it became v hard to start due to an electrical? issue.
If my alternator has had some or all of its diodes die. Will the AC current enter the cars electrical circuit? will the AC current damage anything?  (Please not the ecu!!)
The auto sparkie at first glance said its probably a diode issue, as the brushes altho only 5mm protuding still showed good wear surfaces. The slip ring still showed Copper, altho grooved.. So he concluded diodes... Will hear back today how it went on the test bench.

[Colin Edwards]

The output from a good alternator has a fair bit of ripple in it.  Its not even close to pure ruler flat DC.  Excessive ripple due to open or shorted diodes can hurt capacitors in the long term. 
As long as you don't continually drive and ignore the alternator light and keep externally charging the battery to keep the car on the road.................................?

[cc]

Hi Col
thanks. Well the alternator performed fine on the test bench.....
Altho the auto sparkie said the spring pressure on the brushes felt low. Im picking it up tomorrow with a new regulator and a skim done on the slip ring. A clean up too as it was a bit oily. Probably  from the leaingk low pressure power steering pipe under the radiator.

[Colin Edwards]

The cause of your alternator dramas was probably a sticky brush.  If the brush doesn't contact the slip ring correctly it will usually wear more rather than less.
The grey / charcoal colour / coffee colour surface on the slip ring is VERY important.  It should not be removed.  This "skin" on the slip ring is graphite like material deposited from the carbon / graphite brush.  The two graphite surfaces will feature very low friction.  if the "skin" is removed it has to be re-deposited from the brush.  Until the skin is fully laid down, the brush will erode as friction will be high.  See if you can put new (longer) brushes in the alternator.  Also NEVER use silicon RTV or similar stuff in and about an alternator.  The silicon and carbon react - end result silicon carbide!!!

[cc]

thanks Colin