Repairing a triac dimmer

[Juno99]

Hi, I’m trying to repair a triac dimmer for a stand lamp.
I already installed a new potentiometer, triac (BTA 08 600B) and diac, but its still not working. The problem is that, regardless of the position of the potentiometer, I get a constant output voltage of 48V.
What could cause this problem? I attached the schematic for better clarity.
I also checked the capacitors with a component tester and while C2 seems ok, C1 has a value of only 87nF.

[Kim Christensen]

Are you measuring the 48VAC across the lightbulb? ie: Is the lightbulb glowing dimly?

[Audiorepair]

What type of lightbulb is the "lightbulb"?

[schmitt trigger]

The question from Audiorepair is relevant. Triac dimmers were designed when incandescent lamps were the norm. In other words, a simple resistive load.

[Juno99]

What type of lightbulb is the "lightbulb"?

Currently the "lightbulb" is a resistor. But when I tested it with an incandescent lamp, it glowed dimly.

[Juno99]

Are you measuring the 48VAC across the lightbulb? ie: Is the lightbulb glowing dimly?

yes exactly. For testing purposes i switched the lightbulb to a resistor

[fzabkar]

The problem is that, regardless of the position of the potentiometer, I get a constant output voltage of 48V.

To me this suggests that the resistance of PT1 is insignificant when compared to R2. That is, R2 must be too high in value.

[floobydust]

That the new triac is stuck partially on is strange.
Are these cheap chinese triacs? I've seen them generally terrible quality - they go flaky, low sensitivity, short to the gate and cook the potentiometer.
OP I would check the potentiometer's resistance as it's turned, looking for open-circuit spots. But none of this explains the 45V, unless snubber C1 is bad. What values are R2, R3?

[Juno99]

That the new triac is stuck partially on is strange.
Are these cheap chinese triacs? I've seen them generally terrible quality - they go flaky, low sensitivity, short to the gate and cook the potentiometer.
OP I would check the potentiometer's resistance as it's turned, looking for open-circuit spots. But none of this explains the 45V, unless snubber C1 is bad. What values are R2, R3?

All replacement parts are genuine from a trusted vendor. I'll measure the resistor values this evening.

[Juno99]

To me this suggests that the resistance of PT1 is insignificant when compared to R2. That is, R2 must be too high in value.

Yeah you were kind of right. So the value of R3 is 47 Ohms, but R2 is internally open. Unfortunately the resistance is not legible anymore. What would a typical resistor in this application?

[fzabkar]

I think something like 4.7K - 10K would be suitable.

https://www.google.com/search?q=triac+dimmer+circuit+diagram&tbm=isch

[james_s]

Glancing at other dimmer circuits floating around the web suggests that 10k is probably a reasonable value to try.