Learn Hardcore Portuguese (Brazil): A tela ficou preta quando o celular quebrou. - The screen went black when the cellphone broke.

A tela ficou preta = the screen turned/became black (it changed to that state).
Using ser (foi preta) would sound unnatural here, because ser is more about identity/essential characteristics, not a transition.

Why is it preta and not preto?

Adjectives agree in gender and number with the noun they describe.

tela is feminine → preta (feminine singular)
If it were masculine, you’d use preto (e.g., O visor ficou preto).

Why is there an A in A tela? Do I always need the article?

Portuguese frequently uses definite articles (o/a/os/as) where English might skip them. Here, A tela sounds natural because it refers to the specific screen in the situation (the phone’s screen).
You can drop the article in some contexts (headlines, notes, very informal speech), but A tela ficou preta... is the normal, neutral phrasing.

Is tela specifically “phone screen,” or could it be any screen?

Tela is general: screen/display (phone, TV, computer, etc.). Context tells you which one.
If you want to be explicit, you can say:

A tela do celular ficou preta quando ele quebrou. (= The phone’s screen went black when it broke.)

What’s the difference between ficou preta and estava preta?

ficou preta focuses on the change: it became/turned black.
estava preta describes a state in progress at some moment: it was black (no emphasis on the transition).
So your sentence highlights that the screen changed to black at the moment of breaking.

Why are ficou and quebrou both in the simple past (preterite)?

Portuguese uses the pretérito perfeito (ficou, quebrou) for completed events. The sentence presents two finished actions:
1) the screen turned black
2) the phone broke
Both are treated as punctual/complete events in the narrative.

Does quando automatically require the preterite?

No. Quando can be followed by different past tenses depending on meaning:

Quando o celular quebrou, a tela ficou preta. (specific completed event)
Quando o celular quebrava, a tela ficava preta. (habitual/repeated in the past: “Whenever it would break…”)
Quando o celular estava quebrando... (ongoing process, less common for this meaning)

Does this sentence imply the screen went black because the phone broke?

It strongly suggests a connection in time and likely cause, but grammatically quando mainly expresses when (time). If you want to explicitly express cause, you could use:

A tela ficou preta porque o celular quebrou. (= because)

Could I switch the order: Quando o celular quebrou, a tela ficou preta?

Yes, that’s completely natural and very common. The meaning stays essentially the same; it just changes what comes first (time clause vs main clause). If you start with the quando clause, you typically add a comma:

Quando o celular quebrou, a tela ficou preta.

Why is it o celular (masculine)? Is celular always masculine in Brazil?

In Brazilian Portuguese, celular is normally masculine: o celular. That’s the standard everyday word for a mobile phone. (You’ll also hear telefone or telefone celular, but celular is the most common.)

Can quebrou mean “stopped working” even if it didn’t physically break?

Yes. Quebrar is often used colloquially to mean to break / to stop functioning for devices:

Meu celular quebrou. = My phone broke / stopped working.
It doesn’t have to imply visible physical damage.

Is there any nuance between ficou preta and apagou?

Yes:

ficou preta describes the result: it ended up black (the screen shows black).
apagou (from apagar) focuses on the action “turned off/went out”: A tela apagou = the screen went off.
Both can be true in real life, but they emphasize different aspects.