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While inserting a new DDR4 RAM module in the second slot of my laptop, I broke one of the capacitors (see image).
To my surprise, my Windows 10 started normally indicating that new RAM is available (24 GB in total). It seems to work normally. I ran Memtest by HCI Design with full RAM coverage and it didn't report any errors.
Is it safe to use such broken RAM? May it somehow break my hardware or software?
From an electronics design background that is almost certainly what is known as a "filter capacitor".
It connects a power or data line to ground in order to filter out high frequency noise. Depending what line it is on it may be just some extra protection.
If your memory is operating at the cusp of limits then a broken capacitor may cause the chip or some lines within it to be slightly noisier than expected.
What will happen is difficult to say though. Everything might well work fine for years with absolutely no problems or errors, you might get a bit error in memory once a week, or you might have an entire memory bank dead.
If it came to you damaged then send it back as such.
If warranty return is not an option, or you are just curious if everything is fine anyway, then there's no harm in running Memtest86 and seeing if it works.
By the placement I'd assume it's a decoupling/bypass capacitor. Although there's no guarantee, most products will work fine with a single missing decoupling capacitor.
You might want to make sure the PCB pads aren't shorted, but from the picture it looks fine.
You could have a higher chance at bit errors, so performing a memory test is a good idea. Decreasing the memory frequency could help if you get any errors, although I think this is unlikely to be needed.
I've designed many boards for many companies. It is safe to use and you won't notice any difference or error unless you overclock to the limits. There are many other decoupling capacitors doing the same job (simply said) and one missing isn't dramatic. Just make sure the contacts are clean and no solder particles are left floating on the module.
I believe you should not use the module. The capacitor is to filter and damp out any “surges” and also to protect the memory in the module. The memory could fail which in turn may corrupt or damage data.
I would remove the module and replace it if this was my machine.
As already noted, that part is almost certainly a bypass capacitor. If the memory is operational, then the part is an open circuit (if it were short circuit the power to the memory subsystem, which includes the DRAM controller would be at 0V and would therefore not be operational at all).
That does not mean you could not develop a short circuit as the debris may migrate and cause one in the future to show but one scenario (there are others). That would not necessarily damage the device or controller but that depends on many factors such as power sequencing. It is possible such an issue could cause the local voltage regulator on that particular power rail to self-destruct (that depends on whether short circuit protection has been provided).
Many complex logic devices have a need for a specific power up / power down sequence as there are very often numerous power rails attached and an incorrect sequence can break down barriers between power domains. When that happens, it is possible to render the part damaged to the point of requiring replacement.
If I were not sending the module back, I would remove the old capacitor and probably fit a new one.
The effect of not having that particular bypass device present will be data transfer errors, and possibly refresh errors (refresh is required in dynamic memories as the data is stored internally on a very small leaky capacitor formed by the gate to channel of a MOSFET).
If the damaged part were completely removed it would probably have little effect apart from the previous paragraph (and certainly nothing physically catastrophic to the memory) as modules are designed to a particular requirement which includes power.
It depends what you mean by "safe".
If safe = "won't cause my computer to burst into flames" then probably yes. The component you knocked off is a capacitor which is used for ensuring stable voltage supply to the module. Since you haven't bridged the contacts otherwise, there is no electrical hazard here to the module or anything it's connected to.
If safe = "will run at its rated frequency" then possibly no. In the case of a memory module, such a capacitor is likely to be used to ensure that the contents of the data sent to the module remain stable and do not arbitrarily change due to voltage instabilities. The end result is that without that capacitor, the module is more likely to suffer from data errors. At higher frequencies more capacitance is required to prevent data corruption in the module, so it may no longer be able to reach its rated speed.
If safe = "won't corrupt my data" then almost certainly no. As per the previous point, that capacitor was put there to ensure data integrity, without it you are more likely to get odd errors such as bit flips.
However, "more likely" does not mean "will". If your PC has a good quality power supply and/or your motherboard is a higher-end one with more circuitry for the RAM, the voltage signal sent to the RAM will be more stable, and thus it's less likely the missing cap will matter.
Personally, I would replace the module regardless of the cost. Memory test applications are generally only able to diagnose extremely obvious faults in memory modules, i.e. not the type of transient errors I mentioned. It's entirely possible to have a module pass a memory test and immediately fail when a different application causes it to be accessed in a different way. So don't trust MemTest too much.
Finally, it should go without saying that all of the above is void should you attempt to apply more voltage to this module or increase its frequency (e.g. for overclocking).
