Link to Bosch oven circuit diagram anyone?

[spamlet]

Hi all,

After some searching I have been able to get a replacement oven bottom element for our Bosch HBN6450GB/02 cooker.

It turns out that the replacement is of a sturdier design than the original, which looks promising, but a closer look at the spec leaves me a little puzzled, and I hope the experienced among you can explain.

Bosch site's exploded diagrams seem to leave out the electrics, otherwise, perhaps I wouldn't need to ask...

The assembly has an inner and outer ring, and four contacts in a line. Wires are white; red; brown; orange, and were originally connected in that order looking from the back of the oven.

What is confusing is that the inner ring is marked as 86/75V, but when I check the leads, they seem to be 250V throughout.

Have I got another problem elsewhere that has upped my 75V contacts, or is there some peculiarity of this particular model, that lets it run above the element rating?

For some time before the final failure of the old element - the inner, '75V' ring being the one that failed - the oven had had the very irritating habit of 'resetting itself to 150 deg'. 150 on the display is where it rests even with no element, so presumably it just meant the circuit was intermittently going open as the element deteriorated.

Anyone know where a DIYer can get a look at the necessary diagrams or service manual?

Much obliged for any light the experienced here can throw on this situation.

Cheers,

S

[Ron Lowe]

The markings you have found will not be voltage ratings. They are some other marking.

The elements will operate from standard 240v AC.

Just replace the wires in the same sequence ( so the same wires connect to the outer element, and the same ones to the inner element. )

The issue with the 150 degrees is likely a seperate issue.

[spamlet]

Thanks Ron, that's more reassuring than what I was getting from the rather cagy engineers on the UKWhitegoods forum.

I have found, after entering the part number in Google, the following link for the German part's description:

in case you miss the link on that page, here is the link they provide for the details of the original piece: is an admirably well sorted web site, but, not being a German reader, I have not found any links to circuit diags of the ovens themselves. However, you can see what I mean about the voltage indications for the inner rings. If they do not mean that the inner ones are meant to operate at a lower voltage, what is your interpretation of what they mean exactly?

Even if you don't know the answer, I think you will find the site interesting!

Many thanks,

Steve.

[Richard Skeen]

the URL into does a reasonable job of translating the web page from German to English.

Especially since the outer ring is marked 230V which is the standard European mains voltage these days, it's hard to think that the inner ring marking of 75/86V is not a voltage rating. Perhaps it's connected in series with other elements in the oven, which would explain why you still measure full mains voltage across the leads without the element connected, although that's just a guess.

Rich.

[spamlet]

>>> And, in case you miss the link on that page, here is the link they

> Putting the URL into does a reasonable

Thanks for the tip; and the idea sounds a possibility. Really a pain not being able to find a wiring diagram!

Cheers,

S

[spamlet]

>>>>> And, in case you miss the link on that page, here is the link they

>>> Putting the URL into does a reasonable

Update: SOLVED,

Cheers for helping point the way Rich and Ron. Other tips from a friend included trying making up loads with tungsten light bulbs.

4 in parallel of which, turned out to be roughly 10ohm for the inner ring, and 1 x 60w approximated to the 60 odd ohm of the outer one.

After checking that the voltage did drop across the inner ring - which did turn out to be in series with the grill element - , but only to 140v, I then moved up to putting a kettle in place of each element in turn. Where upon the volts dropped further to 100 odd on the inner connection. Thus assured of no serious risks in hooking up the new element assembly, it was connected, and ran with the indicated 75V - very satisfying.

Had I thought of this latter method in the first place, it would have been much easier, as it is obvious, if you use the same level of cold water in the kettle prior to each test, that the one that boils the kettle quickest is the one that maintains the highest voltage in use.

This little conundrum might have been easier to solve without the peculiar colour choices for Bosch wires: the mains live for example, is, inside the machine, joined to BLACK!

And, try as I might, I could find no reason for one element having a red 'live' and the other, orange.

It also turned out that there was a loose spring in one of the multiswitch's contacts, which had been causing a secondary intermittent problem with the read out for the grill, so it was quite a useful exercise to have had to look more deeply into this than when I first thought of the '15 minute job' changing the element!

Many thanks to all who replied.

S