Dura Ace 7803 Triple Front Derailleur

Having a real nightmare with the above.

52-39-30 chain rings paired with a matching triple lever.

Setting this up as per instruction. Big sprocket at the back and small at the front. Adjusting the limit until the inner FD plate barely touches the chain.

Chain shifts ok to middle chainring but when trying to shift back down to small chain ring the outer plate of the FD doesn't come near the chain to force it down.

Its on an Argon 18 with a weird braze on mount. Its as if the gap between the two derailleur plates is too large.

For clarification I am a competent mechanic.

Correct spacers on crank axle?
Front mech parallel to chainrings? Height right above chainrings?
Shifters both functioning freely? (I say this as there are numerous trim positions on st-7803 levers. If it wasn't quite releasing then this may inhibit a full downshift).

If all ok I think you just have the low limit screw set too close, maybe back it off a touch.

I take the cable and cable guide are in good condition and run freely? Any resistance will be manifested in a downshift to the small chainring on a triple.

All of the above carried out. The cable guide had a good flush out and a floss.

If I back the limit screw off enough to shift down the chain drops.

The solution may be to install a chain catcher but it shouldn't be.

Cheers for the response.

No exactly you shouldn't have to. Doesn't make sense tbh. If the cage is in the right position for the small ring to start with, the outer cage will be roughly level with the middle ring. It can't not derail the chain down when you shift down. Triples are usually a piece of cake compared to some compact systems, I've just fitted full NOS 6603 ultegra to my wife's bike, that just worked from the off. I've no reason to think why 7803 would be any different.

You mention the odd braze on mount, any chance of a pic?

Thinking more about this, what size front rings does the bike have? If a 30/39/50, you may need to run the mech higher (ie more than the usual 2mm gap) so it's inner plate doesn't foul and get caught on the middle ring.

Edited to say just re-read first post. Ignore that.

I've got it sorted. It just took some very precise adjustment. Still not great but the guy has told me he previously had to shift the derailleur by hand so anything I've done is a huge improvement.

Also was running a miche supertype 52 chainring which didn't want to pick the chain up from the middle ring so I've switched it for a shimano 50T and running much better.