Twelve common faults, fixed

1. Two modules won't join — track tops sit at different heights

Diagnosis — the standard fixes the rail top at 70 mm above the underside of the baseboard, equivalent to roughly 55 mm above the table when the standard 25 mm-adjustable feet are wound to nominal. If two modules don't agree, one of them is almost certainly using a different reference. The other usual cause is feet wound out a long way to compensate for an over-thick baseboard, which then doesn't match its neighbours.

Fix — meter both top heights with a steel rule referenced from the table or a flat board. Differences of less than about 1 mm are normally absorbed by winding the feet of the lower module up to bring it to its neighbour. A structural difference — wrong baseboard thickness, trackbed at the wrong height — needs the trackbed rebuilt, not bodged. Do not shim under the Unijoiner: that solves the join briefly and creates a permanent kink that will derail short-wheelbase stock for the rest of the module's life.

Prevention — measure rail-top from the underside of the baseboard before laying track, not from the table. The underside is the reference the standard cites; the table varies.

2. Modules join cleanly but a train derails crossing the join

Diagnosis — three possibilities: a vertical step too small to see at a glance, a horizontal kink (track on one module is angled relative to the module end), or a gauge pinch where a Unijoiner has been over-squeezed. Drag a fingernail across the join in both directions: a step shows up as a click; a kink shows up as a sideways nudge against the nail.

Fix — for a vertical step, dress the high rail with a fine jeweller's file: take perhaps 0.1–0.2 mm off the top, feathering 5–10 mm back so the wheel transitions onto the lower rail without a sudden drop. For a horizontal kink, loosen the track screws closest to the module end, square the track to the end with an engineer's square, then re-fix. For a gauge pinch, gently spread the Unijoiner with a small screwdriver tip; if it has been pinched repeatedly, replace it.

3. A train stalls reliably at a particular module

Diagnosis — the two usual culprits are dirty rails on that module or a poor Unijoiner contact at one of its joins. Stalls at a corner or part-way along a long module almost always come back to inadequate feeders.

Fix — clean the rails with isopropyl alcohol on a lint-free cloth. Avoid abrasive blocks: they take metal off the rail, leave micro-scratches that catch dirt faster next time, and reduce useful life. Check the Unijoiners at both ends — replace any that feel loose, look oxidised, or have visible pitting on the contact area. Long modules and corner modules need their own dropper feeders rather than relying on power crossing every Unijoiner upstream.

Prevention — every module longer than a single straight should have its own droppers wired down to a feeder bus, not depend on Unijoiner contact for power continuity. Clean rails before every running session, not only when something stalls.

4. The whole layout has no power

Diagnosis — work systematically from the feed module out: feed module itself, then the Unijoiners around it, then the controller lead. Don't pull the layout apart from the far end first; you'll waste an hour and probably introduce a new fault.

Fix — put a multimeter across the rails at the feed module first. If voltage is present at the feed but absent on the next module, the Unijoiners between are the suspects. If voltage is absent at the feed module too, work back: RCA leads, plug, controller terminals, controller power. The most common cause is a kicked RCA lead at the back of the controller.

5. Front track works, back track is dead

Diagnosis — three candidates: the rear feeder isn't actually connected, the rear feeder bus has come adrift somewhere in the middle, or one module on the rear loop has reversed polarity and is tripping the controller's overload before the meter sees it. The third is easy to mistake for "no power".

Fix — confirm the rear feed actually feeds the rear track (it's a common mistake to wire both feeders to the front loop and leave the rear loop entirely unfed). Then meter polarity end to end: the red probe held to the rail nearest the module front should give the same reading all the way round the layout. A reading that flips at one module identifies the offender.

6. Module sags in the middle of a long straight

Diagnosis — almost always a warped baseboard caused by sealing only one face. The painted side gives up moisture more slowly than the bare side, and the board cups toward the bare face over weeks or months.

Fix — a small sag often pulls flat once the levelling feet at each joining end are wound up against the neighbouring modules. Severe warps need rebalancing: seal the underside with the same paint or sealer used on top to even out moisture absorption, then store flat under a weight (a stack of books) for a week before reassessing. Prevention is the right answer here.

Prevention — seal both faces and all four edges before laying track. The cost of a coat of sealer on the back is trivial; the cost of a warped finished module is enormous.

7. Skyboard won't sit flush against the baseboard

Diagnosis — three causes: the skyboard is mounted out of vertical, the fastener holes don't line up cleanly, or the skyboard itself is bowed (commonly when a single-thickness sheet has been stored leaning against a wall).

Fix — loosen the fasteners, square the skyboard to the baseboard with an engineer's square held against the rear face, then re-tighten while holding it true. A bowed skyboard usually pulls straight if a thin batten is glued vertically along the back, behind the painted face — the batten doesn't have to be substantial, just enough to resist the bow.

8. Bent Unijoiner

Diagnosis — Unijoiners are sacrificial parts. Once a joiner has been splayed or bent, the contact area drops, and you'll meet problem 3 (stalls) shortly afterwards. They're not designed to be straightened.

Fix — don't try to bend it back. The metal is work-hardened where it deformed, and it will fatigue and split the second or third time. Lift the rail end gently with a small screwdriver, slide the old joiner off, and slide a new one on. Kato sells them in packets through most Australian hobby shops; carry a small bag in your toolkit.

9. Module is 1 mm too long or too short

Diagnosis — the standard requires that rail ends protrude by exactly the specified length (1 mm) so two modules butted together share a single Unijoiner cleanly. A module out by even 1 mm either leaves a visible gap at the join or compresses its joiner painfully against its neighbour's.

Fix — too long: trim the rail end with a cutting disc, then dress the cut end with a fine file so the wheel face is clean. Too short: shift the track forward, lift it cleanly, reposition with the correct protrusion, and re-ballast the affected area.

Prevention — build to the standard module lengths (308 mm single, 365 mm corner) and check rail protrusion before ballasting. Ballast and scenery dramatically increase the cost of a "shift the track 1 mm" repair.

10. RCA polarity reversed somewhere

Diagnosis — the BLUE-to-OUTER convention has been violated. One module — almost always one — has been wired with its blue conductor connected to the inner rail or its red to the outer.

Fix — disconnect everything, meter each module's RCA jack against a known-good reference module (or a piece of paper with red and blue marker stripes corresponding to the rail orientation), and re-solder the offender. Mark the corrected module visibly — a sticker on the underside, a note in its log — so you don't catch yourself out a second time.

11. DCC shorts on a turnout at a module join

Diagnosis — many older T-TRAK modules were wired for DC, with no frog isolation because none was needed: the section beyond the points was simply dead until the turnout was thrown. A DCC booster, plus a power-routing turnout sitting next to a DC-wired neighbour, shorts across the frog through the Unijoiner the moment power is applied.

Fix — cut isolation gaps in both rails immediately past the turnout's frog, so the rails crossing the module boundary are electrically independent of whatever the frog is doing. Or replace the offending turnout with a DCC-friendly type that already has the isolation cut and a separate frog feed. Either fix the module or fix the turnout — the goal is the same.

12. Module won't fit its transport tub

Diagnosis — the standard 57 L storage tub only accommodates a module with the skyboard removed. Many builders glue the skyboard on permanently, then discover at packing time that the assembled module is too tall to close the lid.

Fix — mount the skyboard with thumbscrews or wing nuts driven from below, so it lifts off in seconds for transport and slides back on equally quickly at setup. Already-glued skyboards either need a rebuild with removable mounts, or the module ships in a soft-walled bag with the skyboard up — workable, but the skyboard is more vulnerable that way.