Diode Boards

These photos are of diode boards used on BMW motorcycles made in the late 70’s and early 80’s – in particular, my ’84 R100RS.  I’ve read that these boards are also used on some Moto Guzzis from these years.

The right board in the top 3 photos and the top board in the 4th photo are of the diode board that I just removed on my bike.  I’m guessing it may be original – or one installed in the bike’s first few years.  The left and bottom boards are of a new part.

I am evaluating the old board for signs of wear – particularly heat stress.  And I’m comparing the two boards for differences.  Doing simple electrical tests, both diode boards appear to function properly.




Photo 1: The new board is obviously cleaner, and has different markings on the 6 large diodes.  On the new board (left), three of the large diodes are labeled 041-N and three are labeled 042-N.  (the difference is these diodes pass current in different directions.)  On the old board, the diodes are labeled E1110 and E1120. I’m trying to find out if these different diode types have different capabilities in terms of their rated load and heat capacity.

I have been able to locate datasheets (in German) for the E1110 and E1120 diodes on my bike’s diode board:



I’ve not yet found datasheets for the new diode board’s diodes marked 041-N and 042-N.



Photo 2: This photo shows some differences in the physical construction of the diodes on the two boards.  The new board (left) has somewhat smaller diodes.  Besides the 6 large diodes on each board, there are small diodes inside the board.  Theses are physically much smaller in the new board.  The older board (right) also has wires spot welded to the large diodes to connect them to the PC board.



Photo 3: The old board (right) has grey paint that is flaking.  I’ve read that the grey paint signifies that this board was made by BOSCH.  The new board (left) is made by Wehrle. A version of this board made by Wehrle were defective.  The diode leads didn’t make proper contact with the PC board, resulting in heat build up that melted the solder.  In the early 80’s, I replaced the diode board 2 or 3 times on the new ’84 R100RS I owned because of this problem.  In this photo, I can’t detect any failure of the diode solder connections.



Photo 4: This photo shows the two part number stamps.  The board from the bike shows part number: 1 244 063 3.  The new board shows part number 11 244 063 04/14. I’m guessing that these are the same part number – the trailing “3” and the “04/14” are possibly date stamps, and the older board is missing “11 2” at the beginning because BMW enhanced it’s part numbering system.


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