Learn Hardcore Turkish: Montaj tamamlanmadan önce ekipman listesi kontrol ediliyordu. - The equipment list was being checked before the assembly was completed.

Taking the verb stem (e.g. tamamlan- from tamamlanmak, to be completed)
Adding the negative suffix -ma/-me → tamamlanma-
Adding the ablative case ending -dan/-den → tamamlanmadan
Following it with önce (before)
Together, tamamlanmadan önce = before it was completed.

Why is the verb tamamlanmak used instead of tamamlamak?

tamamlanmak is the passive form to be completed, while tamamlamak is the active to complete (i.e. someone completes something). Here the focus is on the assembly process itself being finished, not on who finishes it. Hence the passive infinitive tamamlanmak.

Why is tamamlanmadan used instead of tamamlamadan in this sentence?

Because the action of completing refers to the assembly itself being completed (passive). tamamlamadan would use the active stem tamamla- (to complete something), implying “before someone completes the assembly.” But since the assembly completes itself (it reaches a finished state), we use the passive stem tamamlan-.

How do you form the passive progressive past tense as in kontrol ediliyordu?

You stack three suffixes on the verb root (here et- from etmek, to do/make):

Passive marker -il/-ın/-un → edil- (root becomes edil-)
Progressive (continuous) tense -iyor/-iyor → ediliyor (it is being checked)
Past tense -du/-dü/-tı/-ti → ediliyordu (it was being checked)
So kontrol et-
- il
  - iyor
    - du → kontrol ediliyordu.

What is the difference between kontrol ediliyordu and kontrol etmiyordu?

kontrol ediliyordu = it was being checked (passive voice; the list undergoes the action)
kontrol etmiyordu = (someone) wasn’t checking (active voice; an unspecified agent isn’t doing the checking)

Why is there no explicit subject in the sentence?

In Turkish passive constructions, the agent (doer) is often omitted if it’s unknown, unimportant, or generic. The focus is on the equipment list being checked rather than who checks it. Hence no subject pronoun appears.

Why is montaj in the nominative case rather than accusative or another case?

montaj (assembly) is the logical “subject” of the phrase montaj tamamlanmadan önce, but since it appears in a temporal adverbial clause (before assembly was completed), it stays in the default nominative case (no suffix).

Could you use bitmek instead of tamamlanmak? What changes?

Yes. montaj bitmeden önce means before the assembly ended.

bitmek = to end/finish naturally
tamamlanmak = to be completed (often with an implication of someone finishing it)
The nuance is slight: bitmek is more neutral, tamamlanmak may imply a planned or formal completion.

Can we change the word order to Ekipman listesi montaj tamamlanmadan önce kontrol ediliyordu? Does the meaning change?

No real change in basic meaning; Turkish allows flexible word order. You place the most important or new information at the end for emphasis. Original order emphasizes the time clause first; the alternative emphasizes ekipman listesi before the verb.

What is ekipman listesi, and why is it treated as a compound noun here?

ekipman listesi = equipment list. It’s a noun phrase where ekipman (equipment) modifies listesi (its list). In Turkish compounds, the first word describes the type, and the second carries the possessive/genitive meaning: listesi literally means its list, but together they mean list of equipment.