Robin – They can be a sod to set up, but on YouTube is a film from a gent who goes through the whole alignment thing in a logical sequence. I'll try and find it and post it here. There is also a forum dedicated to making them work better. If you can't get the blade to track correctly it's probably the fault of the blade, not the saw. This is where throwing away bimetal blades brings tears to your eyes.
Start with a new blade, and remove the blade guides completely. Run the blade just simple round the two wheels. Incidentally to the best of my knowledge they are meant to be metal on metal contact. I do the blade tension pretty damn tight to make sure it doesn't slip, because the instant it does slip off it comes. You may need to fiddle with the alignment knob to get the blade to run quietly on the two wheels without tracking off. There's a small flange on the inside of each wheel, it is possible to get the blade to climb this shoulder but this wrecks the blade. The blade needs to sit on the perimeter of both wheels, secure against the flange of one (or ideally both) of them, with the teeth overhanging the edge of the wheels.
If you can't get the blade to stay on without the guides, there's no hope.
If the blade will stay on, now introduce the blade guides. These put quite a lot of force on the blade, but essentially the less the blade guides lead the blade away from the basic path of the blade the better. The guides should twist the blade into the vertical, not displace it sideways.
Don't make the rollers tight on the blade, they only need to guide the blade not pinch it. Set the top (depth) rollers first, now the inside roller, then the outside roller. On mine I had to file some of the slots to get all this to happen. Don't make the rollers tight on the blade. You should be able to turn them without moving the blade – but the difference between just right and too tight is probably 0.1 mm or so.
It's not true that the blade has to be precisely vertical. It only has to be vertical enough that the kerf cut by the teeth clears the back of the blade. It's the fall of the blade through the work piece that cuts true vertically, and the angle of the vice jaws that sets it square and true in the horizontal plane. So to get a square cut the work piece needs to be held square to the blade in two planes, one of which is parallel to the axis of the hinge. The guides make sure the teeth run in the bottom of the kerf. If the back of the blade rubs the kerf it'll cut round corners, and in a thick work piece this is guaranteed to jam the blade, off she comes. The blades suffer from forming a convex section anyway, unless the guides are adjusted just right not too tight.
The other fault these saws suffer from is that cutting abrasive or hard materials (e.g. stainless) knocks the set of the teeth off, now the kerf of the blade is reduced and the back of the blade rubs the side of the kerf. This is going nowhere!
Unless there is something really out of alignment in the frame (which the no guide test will show) it should be possible to adjust it to work very happily. It seems some of these saws are such a pain to set up they never do an honest day's work, just get sold on but making the adjustments in a logical sequence will solve all that. "Adjustment" may need to include modifying the mountings for the guide rollers.
Good luck, do let us know how it goes. It's worth persevering.
Edit – Neill beat me to it – again!
Edited By Simon Williams 3 on 27/10/2017 21:45:10