My Q died out of warranty and I’m trying to find the fault at board level rather than pay $200 + $200 shipping for an RMA that may come back “unrepairable, no compensation.” I’m one number away from knowing whether I’ve found the fault or I’m chasing a ghost.
The ask: if you have a working Q and are willing to spend five minutes inside it, I’d love one number. Procedure is in the image — unplug, undo four screws, lift both busbars off the hashboard, and measure between the two nickel blocks on the 200 Ω range, both probe directions. Please also tell me what your probes read shorted together so I can subtract your lead resistance.
Mine reads ~12 Ω, rock stable, identical both directions, and identical on the 200 Ω range, the 2 kΩ range and in diode mode. I genuinely don’t know whether that’s normal for this board or whether it is the fault. One reading from a healthy Q settles it either way — and if it turns out 12 Ω is normal, that number is worth having written down somewhere for the next person.
Context, in case it helps anyone else:
The board is AM04_A3197S_UART_X80X2 — 160 A3197 chips wired as two series strings of 80. The 22.5 V rail isn’t regulated by the PSU at all; it’s just 80 × ~0.28 V of chip core in series. Power maths confirms it at three different loads (Eco 31 A / ~690 W, Super 58 A / 1452 W).
Symptom: boots fine, all 160 chips enumerate, PVT voltages uniform at 268–287 mV. Ramps to full current for about 7 seconds of real work, then the load collapses and the telemetry freezes — PVT and temperature arrays byte-identical for minutes. Sits ~6 min at 1–2 A, watchdog reboots, repeats forever. BOOTBY 0x11. Zero error flags for weeks.
Ruled out by measurement, not assumption: mains and smart plug (ran direct from the wall, fault persisted), busbars and joints (no measurable drop at 31 A, and the machine carried 58 A), PSU (holds 22.5 V at the board terminals under load), temperature (42 °C at the Eco collapse, 69 °C at the Super collapse), factory reset (no effect).
After one Super-mode run at 58 A / 1452 W it degraded further: a standby→on cycle now leaves the PSU sawing 0↔25 V with a ~2 s period, and the first error codes of the whole investigation finally appeared — ECMM 128, then latched ECHU 2 / ECMM 4096.
On the board so far: F1 intact, L1 intact, TPS55340 (U161) switch not shorted, no burn marks anywhere under the heatsinks.
Second ask: has anyone else had a Q fail? A few people here have mentioned it. I’d like to compare symptoms — if there’s a common failure point, I’d rather find it and learn to fix it than write these machines off.
