hosyoukikan wo kakuninsita okage de, syuuri ga hosyoutaisyou da to wakarimasita.

A natural breakdown is:

• 保証期間を確認した = checked the warranty period
• おかげで = thanks to that / because of that
• 修理が保証対象だ = the repair is covered by the warranty
• と分かりました = I found out / I learned that

So the whole sentence means something like:

Thanks to checking the warranty period, I found out that the repair is covered by the warranty.

A more literal version would be:

Because I checked the warranty period, I understood that the repair is a warranty-covered item.

おかげで means thanks to ..., because of ..., or owing to ..., and it usually has a positive or favorable nuance.

So:

• 保証期間を確認したおかげで = thanks to checking the warranty period

This suggests that checking the warranty period led to a useful or good result.

Compare:

• おかげで = thanks to, with a positive feeling
• せいで = because of, often with a negative result

So if the outcome were bad, せいで might be used instead.

Because the checking happened before the discovery.

• 保証期間を確認した = I checked the warranty period
• then, as a result,
• 分かりました = I found out / understood

Japanese often uses the plain past form before おかげで when describing the action that led to the result.

So this sequence is:

1. I checked the warranty period.
2. Because of that, I found out the repair was covered.

Using 確認するおかげで would not sound natural here.

保証期間 means warranty period or guarantee period.

It is made of:

• 保証 = guarantee / warranty
• 期間 = period / term / duration

So 保証期間を確認した means checked the warranty period.

Depending on context, in English you might translate 保証 as either warranty or guarantee, but warranty period is very natural here.

保証対象 means something like:

• covered by the warranty
• eligible for warranty coverage
• within the scope of the warranty

It is made of:

• 保証 = warranty
• 対象 = target / object / thing that falls under something

So 修理が保証対象だ literally means:

The repair is a thing that falls under the warranty.

In smoother English, that becomes:

The repair is covered by the warranty.

Because 修理 is the subject of the statement 保証対象だ.

• 修理が保証対象だ = the repair is covered by the warranty

Here, 修理 is not the object of an action. It is the thing being described.

So:

• が marks what is being identified or described
• を would mark a direct object, which is not what is happening here

Think of it like:

• X が Y だ = X is Y

So:

• 修理が保証対象だ = The repair is warranty-covered

The と marks the content of what was understood or found out.

So:

• 保証対象だ = it is covered by the warranty
• 保証対象だと分かりました = I found out that it is covered by the warranty

The だ is there because 保証対象 is a noun-like predicate.

Structure:

• [statement] + と分かる = to understand/find out that [statement]

Examples:

• 安全だと分かりました。 = I found out that it is safe.
• 本物だと分かりました。 = I found out that it is genuine.

So in your sentence, だと is part of quoting the statement 修理が保証対象だ before 分かりました.

Because 保証対象 is functioning as a noun predicate, and noun predicates normally use だ in plain form.

• 修理が保証対象だ = The repair is covered / is a warranty-covered item

When that whole statement is followed by と分かりました, the plain form だ stays in place:

• 修理が保証対象だと分かりました

Without だ, the sentence would be ungrammatical or incomplete in standard Japanese.

This is similar to how adjectives and verbs also keep their plain forms before と:

• 高いと分かった = found out that it is expensive
• 行くと分かった = found out that someone will go

For a noun predicate:

• 学生だと分かった = found out that he is a student
• 保証対象だと分かりました = found out that it is covered by the warranty

This is a very common learner question.

In many cases:

• 知る / 知りました = to come to know a fact, to learn
• 分かる / 分かりました = to understand, to realize, to find out

In this sentence, 分かりました sounds natural because the speaker came to understand the result after checking something.

So the nuance is:

• I checked the warranty period and then realized/found out that the repair was covered.

If you used 知りました, it would sound more like simply obtaining the information as a fact. That is possible in some contexts, but 分かりました is very natural when the information becomes clear as a result of checking or investigating.

It is omitted, which is very normal in Japanese.

Japanese often leaves out subjects like I, you, or we when they are clear from context.

So:

• 保証期間を確認したおかげで、修理が保証対象だと分かりました。

naturally implies:

• I checked the warranty period
• I found out that the repair is covered

Japanese does this constantly, especially when the speaker is obviously talking about their own actions or thoughts.

Usually, yes.

おかげで normally implies that the result is helpful, fortunate, or appreciated in some way.

In this sentence, the positive result is that the speaker discovered the repair is covered by the warranty, which is good news.

If the result were negative, Japanese more often uses:

• せいで = because of, due to, with a negative nuance

For example:

• 確認しなかったせいで、保証が受けられませんでした。 = Because I did not check, I could not get warranty service.

So the use of おかげで tells you the speaker sees the result favorably.

It is saying that the repair is covered under the warranty.

In English, we often say:

• The repair is covered by the warranty
• This repair falls under the warranty

Japanese expresses that idea as:

• 修理が保証対象だ

Even though a warranty technically applies to a product or defect, Japanese often phrases it in terms of whether the repair is within warranty coverage.

So this wording is natural and means the repair cost or service is covered.

Yes, depending on how natural you want the English to sound.

A very direct translation of おかげで is thanks to, but in smoother English you might say:

• After checking the warranty period, I found out that the repair was covered by the warranty.
• Once I checked the warranty period, I realized the repair was covered by the warranty.

These translations sound natural, but they soften the explicit positive nuance of おかげで.

If you want to preserve that nuance more clearly, use:

• Thanks to checking the warranty period, I found out that the repair was covered by the warranty.

A rough gloss would be:

• 保証期間 = warranty period
• を = object marker
• 確認した = checked
• おかげで = thanks to that
• 修理 = repair
• が = subject marker
• 保証対象 = warranty-covered item / thing covered by the warranty
• だ = is
• と = that
• 分かりました = understood / found out

So literally:

Thanks to having checked the warranty period, I found out that the repair is a warranty-covered item.

That is not natural English, but it shows how the Japanese is built.