Ayah mengganti bohlam bukan karena lampunya terlalu terang, melainkan karena sakelar itu sering tidak berfungsi.

Ganti is the root meaning change or replace.
With the meN- prefix, it becomes mengganti, an active verb meaning to replace something.

So:

• ganti = change / replace
• mengganti = to replace

In Ayah mengganti bohlam, bohlam is the object, so mengganti is the natural form.

Bohlam specifically means light bulb.
Lampu is broader and can mean lamp, light, or the light source in general.

So in this sentence:

• bohlam = the bulb that got replaced
• lampunya terlalu terang = the lamp/light was too bright

English also does something similar: you might replace the bulb, but complain that the light is too bright.

-nya can do several jobs in Indonesian. Here it mainly makes lampu sound definite and natural: the lamp/light or its light.

So:

• lampu = lamp / light
• lampunya = the lamp / the light / its lamp-light

In context, lampunya terlalu terang means something like:

• the light was too bright
• or its light was too bright

So yes, -nya can feel possessive in some contexts, but very often it also just means the in a natural, context-based way.

This is a very common Indonesian pattern meaning:

• not because ..., but rather because ...

So:

• bukan karena lampunya terlalu terang = not because the light was too bright
• melainkan karena sakelar itu sering tidak berfungsi = but rather because that switch often didn’t work

It is a corrective contrast: the speaker rejects one explanation and gives the real one.

In this pattern, Indonesian normally uses bukan, not tidak.

• bukan karena ... melainkan karena ... = standard and natural
• tidak karena ... = unnatural here

A useful shortcut:

• tidak usually negates verbs and adjectives
• bukan usually negates nouns, noun-like expressions, or is used in set contrastive structures like this one

So even if English says not because, Indonesian idiomatically says bukan karena.

Melainkan means but rather, instead, or but instead.

It is usually used after a negation or correction:

• bukan A, melainkan B = not A, but rather B

By contrast, tetapi just means but and is more general.

So:

• bukan karena ..., melainkan karena ... = very precise, corrective
• ..., tetapi ... = a more general contrast

In this sentence, melainkan is the best choice because the speaker is correcting the first reason and replacing it with the true reason.

This is an important distinction:

• terlalu terang = too bright
• sangat terang = very bright

Terlalu implies excess — brighter than desired or appropriate.
So if the sentence used sangat terang, it would only mean the light was very bright, not necessarily a problem.

Here, terlalu terang shows a possible reason someone might replace a bulb.

Sakelar means switch, especially an electrical switch.

It is a standard Indonesian word. In everyday speech, some people may also use borrowed forms like switch, but sakelar is correct and common.

So:

• sakelar itu = that switch

In Indonesian, demonstratives usually come after the noun:

• sakelar itu = that switch
• rumah itu = that house
• buku ini = this book

So this is normal Indonesian word order:

• noun + ini/itu

Not like English that switch, but literally more like switch that.

Berfungsi means to function or to work.

It comes from:

• fungsi = function
• berfungsi = to function / to be functioning

The prefix ber- often makes intransitive verbs, especially verbs meaning something like have, use, be in a state, or perform a function.

So:

• tidak berfungsi = not functioning / not working

In this sentence, sakelar itu sering tidak berfungsi means that switch often doesn’t work.

Sering means often, and it modifies the whole predicate tidak berfungsi.

So:

• sering tidak berfungsi = often does not work

This word order is very natural in Indonesian. The adverb sering comes before the negative predicate it modifies.

Compare:

• sering terlambat = often late
• sering tidak datang = often does not come
• sering tidak berfungsi = often does not function

Yes. In Indonesian, family terms like Ayah, Ibu, Kakak, and Adik are often used without an explicit possessive when the relationship is clear from context.

So:

• Ayah mengganti bohlam naturally means Dad replaced the bulb or Father replaced the bulb

It does not usually sound incomplete to an Indonesian speaker. The possessive idea is understood from context.

Because the sentence is talking about two slightly different things:

• bohlam = the physical bulb that was replaced
• lampunya terlalu terang = the light/lamp output being too bright

This sounds natural because in real usage people often talk about replacing the bulb, but judging the brightness of the light.

So the wording avoids awkward repetition and matches how Indonesians naturally describe the situation.