Trying to fault find a dead PCB and I'm a bit lost on what this component circled is.

Looks like a fuse or protection resistor of some sort but never seen one in a neon tube style capsule. It's on the 240v A/C side of the PCB and labelled is as 'TVS1', where fuses are labelled 'F1' and resistors labelled 'R1' etc. So based on the labelling it's neither. It tests as open circuit on the multimeter and there's no other markings on it.

I'm guessing it's some sort of anti-surge/lightning capsule, but I've only ever seen them made of ceramic

Any ideas?

 

TVS1 .is a description for transient voltage suppression. it shunts current when excess voltage spikes. A type of avalanche diode. It will probably have a high resistance and be across the supply

If the board is dead and with no obvious damaged/burnt up components, you're likely looking for a high value resistor gone open circuit. What type of equipment is the power supply from?

 

So I was on the right lines.

It's a inverter drive and logic board for a Gree split air-conditioner outdoor unit. Chinese, so no circuit schematics and over ten years old so no spare parts availability. It basically runs a three phase compressor off single phase mains and gives variable compressor speed by adjusting the phase frequency.

Seems to be dead on the logic-side as the diagnostic LEDs are not working, and indoor unit gives a 'no-communication' error code.

It's just a case of plodding through 'til I find something. I have stable DC out the main bridge rectifier for the compressor drive (these usually short out). However there could be a second rectifier just to do the logic circuit (as well as the condenser fan motor).

It's switched-mode with active PFC, and my previous experience has found that the supply regulator chip can shut down if the recitified supply is unstable, usually duff caps...but that's with class-D audio amplifiers, it may be a tad different with an air conditioner - and in the days when I did work on air conditioners they were all fixed speed with much more basic circuitry (except the VRVs which I rarely touched ).

Fun and games

 

Looks more like a gas discharge tube (GDT) to me. Avalanche diodes are usually more none discript.