My trusty TS-440S has been rock-solid for 15 years, but last week during a 20M POTA activation, it suddenly lost all RF output. Power transistors or ICs, but other components may be affected as well (electrolytic capacitors - rare but it happens, diodes, zeners, etc.) SWR meter shows 1:1 on dummy load, but zero watts output across all bands and power levels. Supply voltage is steady 13.8V, fuses are good. Before I tear into the PA section, what's the systematic approach here? Unless the failure can be positively attributed to counterfeit transistors (which will fail at much lower power levels than the genuine device), try to determine exactly what went wrong before re-commissioning the amplifier. Check speaker leads, supply voltages and speaker impedance Should I start with bias measurements on the final transistors or check the driver stage first?

Start with the driver stage - no point checking finals if they're not getting drive. Signal Tracing. Signal Injection. Use an RF probe to trace signal from the exciter through each stage. The 2SC2498 drivers often fail before the 2SC2879 finals in these rigs.

Before you do anything, check the ALC and TX/RX switching circuits. Direct coupled power amplifiers are notorious for "chain failures" where one bad component causes the failure of parts both up and down stream. I've seen bad relay contacts cause exactly these symptoms - full voltage but no RF path to the antenna.

Had the exact same failure on my TS-440S two years ago. Turned out to be the low-pass filter relay sticking in receive position. That means using a variable transformer where needed and possibly a "dim bulb" tester. Direct coupled power amplifiers are notorious for "chain failures" Easy fix once you find it - don't assume it's the expensive parts first!