You can use the onload
event to detect when the iframe has finished loading, and there you can use the scrollTo function on the contentWindow of the iframe, to scroll to a defined position of pixels, from left and top (x, y):
var myIframe = document.getElementById('iframe');
myIframe.onload = function () {
myIframe.contentWindow.scrollTo(xcoord,ycoord);
}
You can check a working example here.
Note: This will work if both pages reside on the same domain.