Bosch oven circuit diagrams?

Hi all,
Some may remember helping with suggestions last year as to why our Bosch (HBN6450GB/02) oven temp might be resetting itself to 150 all the time.
Following advice, we struggled on with the occasional judicious thump, but eventually the fault became apparent with the failure of one of a double ring on elements at the bottom of the oven.
It turned out that with the element actually removed, the display still stays on 150, so this is what it appears to reset to as the element gradually fails and makes intermittent open circuits that the 'odd thump' can get you by for a while.
Anyhow, after much web searching I have obtained a replacement element assembly. This comes with no instructions of course, so to be doubly sure I had the connections right, I checked the voltages of the leads prior to installing.
The two rings of the element assembly are marked with different voltages: 250V for the outer, and 75V for the inner. But when I check the leads themselves (very carefully!) I only find 250V available.
Anyone have more info to explain this before I hook it all back up finally?
Ideally, can anyone point me at a circuit diagram. Typical how one can find any number of service manuals with complex circuit diags for cars: but, apparently, b' all for a basic thing like the kitchen cooker!
Many thanks, (And I hope you beat the spammers!)
S
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In case anyone is interested:
I sussed this in the end, using a kettle in place of each element in turn (using the same amount of fresh cold water each time). The lower voltage circuit takes much longer to boil the water.
Easy, but
Anyone trying this be very careful!
S
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