STI vs FD question that has probably been asked a thousand times.

Having failed to set up two FDs (6600, 5700) on two different bikes, I am now eyeing the STI as maybe the problem. Does this ring true? In both cases, I was unable to get the FDs to shift from small chainring to large and so, today, have removed the FD entirely.

Here's how it was set up originally...
old steel Raleigh frame with braze-on:
Ultegra 6603 STI (triple)
FD-6600 (double)
FC-6600 (double)

I never got this to shift! I suspected the FD-6600 was just a bit knackered.
I replaced it with...

Ultegra 6603 STI (triple)
brand new FD-5700 (double)
FC-6600 (double)

Still couldn't get it to work properly, but I assumed this was my 11-thumbs approach to bike fixing.
Anyway, I put the bike in for a service, a frame crack was discovered and I had to replace the f + f. BUT, the person doing the service said that he thought my FD was broken because it wouldn't shift. Weird. NEW FD, never been set up. Broken?

I put all the gear on a replacement frame + fork...

carbon Ambrosius Celcius clamp/braze-on adaptor:
Ultegra 6603 STI
FD-5700
FC-6600

STILL couldn't get it to shift, so removed it entirely.
Any ideas how to test if it's the STI without breaking the bank and buying another?! Is the Triple a problem here? TIA!
Paul

Undo the cable from the FD. Pull on the cable to tension it, then try the STI.

Similarly, try to move the FD by hand (mounted on the frame, but disconnected): is it free to move all the way over? Are the stops limiting it?

Assuming they're OK, then I can only think you don't have enough tension on the cable.

Yep, the FD cable should really be just taught when set to the first gear. Then, as soon as you shift on the STI it should start to move the FD. If the cable is too loose when in first gear, the pull on the cable will only tighten the cable and not move the FD.

If you don't have barrel adjusters the best way can be to put the cable through the FD with bolt just loose enough to allow the cable to slip. Pull the FD outboard a little on it's spring, pull the cable tight and tighten the cable bolt. When you release the FD it should leave the cable taught but the FD still hanging in first gear.

Also, check how the FD is aligned to the chainrings. The manual for the FD should give you the optimum position.

Should have been reply to the OP.

@Scilly.Suffolk @Scrabble
Thanks both. It's really good to read these suggestions, as I've tried them already and thought I was going mad!
As a last test, I could only get enough cable tension by pulling the cable through the FD's cable bolt hard with pliers and tightening the bolt - then turning the barrel adjuster full out, to the point where the outer started to corkscrew.
Without this extreme tension, the STI doesn't seem to engage with shifting at all.

Could be I have two bits of equipment that are faulty. Or 'problem exists between chair and derailleur'.

Thanks again!

With the cable loose, can you actually feel cable being pulled by the shifter when you shift?

Good question: YesTERISK.
But it's when the cable is attached and tensioned that the problem seems to be occurring. I have got and old Huret braze-on that I know moves relatively loosely by hand. I might throw that into the mix and see if it works, then take it from there. Thanks!