shower appliance - Grohe 6710S - who can help ?

Hello,
I have a single knob, with handle, wall-mounted shower control valve that is no longer working. I suspect the cartridge but cannot remove the handle and knob to reach it.
I strongly suspect it is part of the "Moen" series, placed in my house 42 years ago... On the back of the handle, it carries the engraving GROHE 6710 S"
I enclose a picture "http://xray227.server4you.net/software/P1120151.JPG with the hope someone could help me with an exploded view or a clue about how to proceed in dismantling the valve to be able to replace the cartridge. I have two kind of catridges at hand: a "Moen" and a "Euromix".
Thanks in advance !

if it says Grohe, then its likely a grohe faucet. pry the front off with a flathead screwdriver, there should be a screq underneith... ( the face of the handle )

Thanks for the reaction. Removing the cap and unscrewing the central screw was easy; I had done it long ago.... But after that, I cannot dismantle anything. Pulling on the knob reveals that the handle remains clamped somewhere. The head is clearly made of two parts, but unscrewing the second part is not possible. I generously used anticalc products with the hope to dissolve any deposits. This did not (yet) help.
Any other clue ?
Robert

I'm not familiar with this particular model, and Grohe does not have a standardized method of handle construction. There appears to be a red screw cover on the under side of the handle assembly but it is hard to see, have you removed that and checked for a second screw?

Any chance of getting a picture with the cap removed?

here is a pic taken afrom the underside of the handle. It clearly shows the item number.
http://xray227.server4you.net/software/P1120154.JPG