This is a write up from my work shop point of view, to help you make decisions when you consider buying a digital piano, whether new or second hand. I have serviced pianos from all kinds of brands, expensive ones, cheap ones.
Maybe you found this page because you were looking for a test or review. This blog post is not about testing pianos of brands like Classic Cantabile, Cronenwerth, Hemingway, Medeli, Schubert or Thomann. Instead, I will provide general information about pianos by these brands based on personal service experience.
Generally speaking the cheaper ones need maintenance earlier, sometimes after just a few month of playing and often because mechanical parts fail. More expensive pianos enter my work shop entirely because intense usage throughout many years makes e.g. the filt dented or electrolytic capacitors need to be replaced due to life cycle ending after some 20 - 30 years or so. Still, they are easily repairable while cheaper pianos will not even last that long for many reasons. Here is why.
1. Failing keys
This happens either due to dust or dirt on contacts because the contacts aren't encapsuled properly, or too little conductive material is applied to them. I've even had a case where corrosion in a cheap connector broke the piano after just 3 years. But since dust is enemy No. 1, as a conclusion, lay something on your keyboard while you are not using the piano. Hopefully you have a cover installed.
Or there is a mechanical problem. I've had torn off and broken hammer rubber and plastic, worn out keys, bent axes. Sadly, the original importers usually refuse to keep spare parts for more than two or three years so you either have to improvise or you have (or add to) a collection of spare parts from trashed pianos. While the European Union has started to force manufacturers to provide spare parts for a certain period of time from 2021, manufacturers of digital pianos are not (yet) among them.
There are brands that have products with really good keybeds, though. Classic Cantabile for example sometimes use keybeds by renowned italian manufacturer Fatar. Usually this is mentioned by adding to the type name on the piano, so in this case at least you'd get away with something sustainable.
2. Failing capacitors
It's electrolytic capacitors that are failing mostly. While good pianos are built on capacitors with a lot of headroom (tolerating much higher temperatures and voltage than expected) the cheaper ones are made of parts that just meet the electrical absolute must. Since a cap life cycle is measured in hours (e.g. 2000 h) they can loose capacitance early and start to fail even if you just left the instrument switched on over night repeatedly. Loosing capacitance often means leakage which leads to other issues also. Symptoms could be low volume on one stereo channel, crackling static noise or low voltage in critical parts of the circuit resulting in complete failure.
I've made the experience that SMD* caps fail more often than through-hole-components although they could be the better choice if selected properly. I have even seen exploded SMD caps due to lack of determined breaking point. You guessed it, SMD components are often cheaper than through hole equivalents.
I observed that in newer products even cheap brands tend to return to through hole components at least for some parts of the circuit which makes maintenance a lot easier. But it would be better if they made this a general rule in my opinion.
One more word about a problem familiar even to high class manufacturers: (Before) some of them like GEM (†), Roland, Technics (†) and even Yamaha use(d) rechargeable batteries to buffer memory when the piano is switched off. These batteries tend to leak after many many years of usage, damage can be dramatic so it's a good idea to keep an eye on that if you own such a piano or plan to buy a used one. If you have a memory function and there is no battery installed (e.g. a standard CR2032) then it's likely that you have something rechargeable instead. Watch out and have that component replaced after 10-15 years latest.
3. Failing pots, faders and switches
This applies generally to all manufacturers of electronic devices. But you can use cheaper or better components for your products. While better pots often can be revived by cleaning them, cheaper ones have their conductive material lost and are only to be replaced. What's more, sometimes it's not easy or even hopeless to get spare parts with the same specification and dimensions.
4. Poor manufacturing quality
In (junk) industrial manufacturing all parts are preconfigured, like predrilled housing screw holes or automatic placement not only on circuit boards. Despite the fact that robots do a lot of the manufacturing work, controlling is essential. Whenever I came across a cheap brand piano I spotted indications of inattentive controlling. Missing or misplaced screws. Badly placed or even wrong parts on circuit boards (while the boards itself fulfilled function testing somehow). Displays and LEDs not fitting their panel spaces (low quality displays by the way that become pale just after a few years). And hot glue on spots where it does not make much sense like on connectors that are self securing or wires that have dedicated supports anyway, always glue, glue, glue. My image of a junk industry controller is of a person holding a signing pen in one hand and a glue gun in the other.
Still, it's kind of sympathetic that the IC's in the above image are marked LOL.
5. Built not service friendly
Especially chinese manufacturer(s? Plural? See below!) seem to save costs whenever possible (presumably pressed by western online- or chain stores). Sadly, this applies also to certain connectors between circuit boards, most of all panel boards. So if some replaceble component failed you have to disassemble all of the boards because all wires are soldered AND GLUED (!) onto the boards. Why do engineers do that? Don't buy that. Nobody wants to repair it.
6. Poor sound quality
These cheap ones sometimes have tons of sounds and functions onboard. But they don't sound good at all. Speaker types and filters are not well trimmed to the housing so that you think a certain frequency range (often low mid) is too dominant. And they tend to have strange dynamics. They are noisy. Even their transformers hum. D/A conversion often sounds like there was no developement since 1983. Take a pair of headphones and listen to a single note while it sustains, how long does it sustain? When is it getting noisy? They're trying to paste up noise with reverb, right? Reverb can't be switched off permanently, right? You got it.
My rule of thumb:
If the total price/button ratio is below 20 € (or dollars), don't buy it.
What kind of digital piano should I buy?
If you don't have much money, rather buy a 20 year old Yamaha, Roland, Technics, Kawai, Korg or a later Casio, than one of these cheap brands that are supposedly manufactured all in the same factory run by Medeli in Zhuhai/China. If there are issues with second hand pianos from the above name brands they are often easily fixed, as long as it's not a leaking-cap-problem (see above). And often you still get spare parts for them even after many years. I have revived digital pianos from the 1980s and early 1990s that still sound better than nowadays 500 - 600 Euro China products.
Questions? Additions? Comments? Insults? Feel free to leave a message below.