Both sets of sentences are correct, the difference between them is the meaning.
Now this difference is a little hard to explain, but I will do my best.
The verb 'to have' conjugates in the present as 'have' or 'has':
- I, you, we, they, you all = Have
- he, she, it = Has
In the past, it conjugates as 'had' for everyone.
Now when it comes to questions starting with 'to have', asking if someone has done something, they are asking about one of two situations, each with it's own meaning.
When you use 'had' (past tense), then you are asking about any time up to a specific moment in the past.
Had you run a marathon?
Meaning "At any time up until that moment in the past, did you run a marathon?", or "Did you run a marathon by then?"
When you use 'have' or 'have', you're asking about any moment up until right now.
Have you run a marathon?
Meaning "At any time up until now, did you run a marathon?", or "Did you run a marathon by now?"
The difference between the two is the limit of the time asked about. When you ask using the past tense of 'to have', then the limit is referring to a specific moment in the past. When you ask using the present tense of 'to have', then the limit is this very moment, now.
- Have, has = "up until now"
- Had = "up until then"
I hope that helps!
Your reasoning is on the right track, in that "had been broken" often would be read as implying agency or intent. However, had broken is perfectly correct here. In fact, you do not go far enough: if the article had said "had been broken," most native speakers would assume that some individual had broken it. There are some definite subtleties here, however.
First, let us recall that some verbs can be both transitive and intransitive. Broke is in fact one such verb. Either a subject can break an object, or an object can break, similar to how one can eat dinner or simply eat. However, since the subject is the physical recipient of the action in the first case, it is not so easy to see.
There are two ways that this sentence could be written, with three interpretations.
The coupler had broken.
Really, this the past perfect way of saying it broke. No agency implied.
The coupler had been broken.
In most contexts, this would imply that some human had broken it.
However, in this context, it would not:
The coupler had been broken for a while.
In this case, broken is merely an adjective, not a past participle, and thus refers to a state, not an action. No intent is implied.
That said, this is Indian English, which is dialectically distinct from the version I speak, so certain rules might be a little different.
Best Answer
I would say that in normal circumstances, people would interpret the following three sentences in the same way:
With each sentence, the implication is that it is now done, or is at least in the process of being done.
The past tense in the first part of the sentence invites a comparison with a differing state in the present. Otherwise, you wouldn't express the idea with the past tense.
Instead, if you want to clearly express the fact that it is still not done, you would use the present tense:
Here, the present tense affirms an existing condition (of it not being done).
If you want to express the idea that it might be done in the future, then simply add that to the present-tense sentences: