Hello,

As a follow-up, I’d like to report that my second RB5009 unit is showing the same issue as the first: visible moisture spots on the casing after just 9 days of minimal use.

Here are the relevant conditions:

The unit was placed freestanding on my desk, in a well-ventilated room at a constant 24°C.

No PoE was used, and it wasn’t connected to any other devices except occasionally my PC via Ethernet to capture configuration screenshots.

It was powered using the official 48V 2A MikroTik power adapter.

The unit remained idle most of the time, with no significant load or heat generation.

Given that this is the second device showing signs of internal condensation or leakage, I suspect a possible manufacturing defect – potentially a leaking capacitor or another component causing internal moisture accumulation.

My reseller has been informed again. I am now reaching out here to ask:

Has anyone else encountered similar symptoms with the RB5009?

Is there any known issue with a recent hardware batch?

Would MikroTik be willing to investigate this more closely?

I can provide photos and serial numbers of both affected units upon request.

Thanks in advance for any input or assistance.

Best regards,

Very odd ... I have 2 of those, both almost 2 years already.
None of the issues you describe.

Thanks for you're reply
This photo shows the second RB5009 unit. The moisture spot is clearly visible after just 9 days of minimal use.
The first router I received showed the same issue, but much more severe, with a larger affected area.
This confirms that the problem is not incidental, and may indicate a structural defect.

Is it really water moisture? It might be some oil or loctite or something from the manufacturing process, IDK?

If unit is kept inside, I'm lost at how that much water could start to leak...although I guess the RB5009 does get hot, so if you have a lot of humidity perhaps... but thermodynamics is not my speciality so IDK.

You can file a ticket at help.mikrotik.com and include the photo since MT may have some clue.

Thanks for the input.
The moisture on the second unit appears to be slightly oily to the touch, which makes me suspect a leaking capacitor rather than regular condensation.
It's definitely not water from the environment — the device was kept indoors in stable conditions (24°C, dry room, no PoE, minimal usage).

The first unit had even more severe marks, which reinforces my concern that this may be a manufacturing or component-related issue.

@OP: There's no need to worry. This is normal.

The rb5009 fits all of its chips that have cooling needs to one giant backplane and heatsink, which is a really nice design decision - I wish it were more common. However this requires the use of thermal interface solutions that can adjust to the "fit" of the chips - some are taller, some shorter, and the *exact* position they rest in after reflow soldering is a bit uncertain. In these application a sort of thermal interface material soaked "sponges" are used, and for them to work properly, they are somewhat compressed when assembled (coming in saturated from their manufacturers.) Some of this ultimately silicone-based stull will leak out - either over time or when exposed to high(er) temperatures. These substances are chosen specifically to be electrically and chemically inert.

Again, this is normal, wipe it off and go about enjoying your day.

EDIT: With regard to some other ideas, moisture is - well - moisture like. You will find that this is oily. A capacitor leaking is much more local, and again the residue is of a a brownish color (which can be determined by wiping it off with a clean white wipe), and is not oily, but instead sticky and has a foul smell.

EDIT2: I have deployed a number of these units and most came with this sort of "artifact". I am somewhat reluctant to say "they came from the manufacturer like this", because this leakage most probably occurs during storage/shipping.

Thank you very much for your detailed and reassuring explanation.
After reading your reply, I tested the residue with a clean white paper, and indeed – it is colorless and oily, not sticky or brown. This confirms your diagnosis: it's harmless thermal interface material, not moisture or a leaking component.

I truly appreciate you taking the time to share this technical insight. You've helped put my mind at ease. I’ll clean it off and enjoy the RB5009 with confidence.

Thanks again!

I recall that there was such problem already discussed on the forum so it happens from time to time.

So it seems...
Example: viewtopic.php?t=214137

All true, and I've mostly seen them. This is why I endevoured to provide a full explanation. If it was a waste of bits - please delete it

What Ethernet cables are connected ?
Where do those Ethernet cables go ( outside ) ?

Follow your ethernet cables - I suspect one or more cables is the source of your moisture problems.

If unit is kept inside, I'm lost at how that much water could start to leak...although I guess the RB5009 does get hot, so if you have a lot of humidity perhaps... but thermodynamics is not my speciality so IDK.

Not really thermodynamics, more like chemistry.

Anyway when humid air encounters a cold surface, the water in the air condensates, the water vapours are in a gaseous state and become liquid.

When a wet surface Is heated the liquid water becomes gas (evaporates).

Even if idle, I doubt that any electric or electronic device can not only avoid creating heat (this is actually thermodynamics) but actually produce cold.

Ok, there are Peltier cells, still ...