LED uplighter dimmer burnt resistor

[CG2]

I've got a 240v LED uplighter which isn't working. Pulling it apart shows a clearly burnt resistor on the circuit board, and I'm hoping some of you will have suggestions on what to replace it with. First, here are some photos. Power comes in, through the fuse and choke, then through the big blue variable resistor labelled B500K (ignore the similar blue component at the bottom - it's a simple switch for an attached reading lamp). It then passes through the burnt resistor (or at least did once), through diac DB1 and the unburned 30 ohm resistor to the gate of the triac.Now I assume there's a simple way to calculate what value that resistor should be, but it's beyond me. If it's relevant, the lamp is supposed to hold two 6W dimmable 240v led bulbs. Thanks in advance to anyone who knows the relevant maths.

[stj]

it's a traditional dimmer circuit with a smaller triac,
not really suited to driving leds - just saying.
is the diac shorted?

[redwire]

I would say the triac is dead, they can go open circuit and then the drive circuit burns up. BT132 is only good for 1A. Check the potentiometer is still OK before deciding to repair or throw it out. It could be burnt the carbon tracks inside near the full brightness end. It should be 500k ohms.
The burnt resistor is around 2.2k 1/4W and up to 10k ohm will work too.
Jing Neng Dual Dimmer Switch JN6230D, JN6230DM-2 repair

[CG2]

Thanks. The triac checks out OK, but it looks as if the diac went instead. The potentiometer is gone as well, but they seem to be available cheaply on aliexpress https://www.aliexpress.com/item/1005005632064132.html The wiring on this is scarily thin. I'm guessing that someone stuck in a couple of 60W bulbs and that killed it.

[stj]

you can get entire dimmer modules for almost nothing on ali,
it may be cheaper to do that and swap the parts over

[eccerr0r]

I'd imagine that DIACs (btw how do most people test these without a high voltage curve tracer?) would fail short or end up blackened/burned, and it's not conclusive here if you see an open DIAC with a modern multimeter?

[stj]

i would just check if a diac is shorted

[CG2]

Is it that hard to test diacs? It looks OK and isn't shorted. My "test" was to connect it up to one of those cheap component testers which said "defect device" The triac checked out OK on the same bit of kit. Those little diacs cost virtually nothing anyway, so I've ordered some, but might try changing just the potentiometer and see what happens.

[stj]

big clive has a video or 2 that are interesting
https://www.youtube.com/watch?v=w71Qr1ygB_Y
https://www.youtube.com/watch?v=SRUzMd3lwLQ