Step 10.78 — SSR polarity and isolation, one last time¶
Step 79 of 80 with a helper · Chapter 10 — Wiring and Checkpoint #1
(no image — see text)
Parts:
- multimeter · tool
Do: Read the SSR terminals with the harness attached: 1 = bed L, 2 = mains L from the brown WAGO, 3 = red from the Leviathan HEATBED, 4 = black.
Check
All five rows, with the harness attached.
Helper Records the five SSR readings the adult calls out; the adult holds both probes.
What you're looking at
The same four terminals as step 10.10, now with all four cables attached, plus one measurement the earlier check could not make: mains side to control side must be open, the relay's isolation barrier being all that stands between mains and mainboard.
| Measurement | Expected |
|---|---|
| SSR 1 → SSR 2 | 100 kΩ or more, or OL, on the 2 MΩ range, close to your 10.19 L↔N number: the bed pad and the PSU input bridge the open relay. Near 0 Ω is a shorted SSR |
| SSR 3 → SSR 4 | the Leviathan's bed output impedance, a finite reading. Not 0 Ω |
| SSR 1 or 2 → SSR 3 or 4 | OL — mains and DC control are galvanically isolated |
| SSR 1 → SSR 2 wire colours | bed cable on 1, brown WAGO cable on 2 |
| SSR 3 wire colour | red |
If mains-to-control is not open, the SSR's isolation barrier is gone. Replace it; do not power the machine.
Source: LDO wiring guide § Connecting 24V · LDO Rev D photo S4 24 V/SSR mapping
