New track compatible with old problem

[Brightonali]

Quick version:
Why won't the second hand Fleischmann n gauge track I just bought work with my existing Fleischmann starter set?

Longer version:
We've had the Fleischmann starter set A + B for about 30 years. Always works. This year I thought it would be nice to get some extra track for a bigger layout and went to local model shop (Off the Rails in Hove) to enquire. The man there happened to have a large biscuit tin full of dozens of pieces of Fleischmann n gauge. £30 for the lot. I went home happy and built a larger layout but none of the new track works.
It looks fine - many pieces visually indistinguishable from mine, some just with remnants of paint from previous owners layout.
It's nothing to do with the layout design. I can get my original loop working with my old track, but substitute any piece of the new second hand track and the loco stops as soon as it hits it.

Any explanation or advice?

I'm not an experienced model railway enthusiast - we just get the kit out once a year or so, but have a grandson now and thought it would be fun to have more to play with.

[Walkingthedog]

Is it clean. I don’t mean does it look clean.

[Steve M]

I would also suspect that the fishplates (track joiners) may well be loose or corroded inside (or both).

[RAF96]

You need a track tester or digi-meter to see where there is and where there isn’t track voltage. Test every piece of ‘new’ track connected together with a known good piece.

[Brightonali]

Thanks, those are all good suggestions, however:
Most of the pieces look clean - indistinguishable from my pieces.
I've tried lots of them, about 20. They don't look like they have loose fishplates. And it's exactly the same with different 'new' pieces in different positions: the locomotive chugs up to the piece nicely and then stops as soon as it hits it. Over and over, different pieces, different places. A mystery?

[Steve M]

I shall reiterate my original suggestion. If the loco stops as soon as hit reaches the 'alternative' track, there must be an interruption in power transmission ie loose track joiners and/or dirty track. Just because it looks clean does not mean it is clean. As Rob says, check continuity with a multimeter.

[Walkingthedog]

Try placing wire between the track joints to see if power then transfers across the joint.

[Brightonali]

Thank you both. I'll try cleaning a piece or two thoroughly and inspecting the connectors more carefully. I just thought it very odd that so many apparently clean pieces, all with connectors that seemed fine, should all behave in the same way. I thought there might possibly be an explanation. I'll report back. Is there capacity to post pictures or video on this forum?

[RogerB]

Yes, you use the “Add image to post” icon just below the box you type in. On the left. R-