Capacitor replacement

IMHO if you are good at soldering (I guess you are) it's always a good idea to replace caps with new ones, even with higher voltage as suposedly they're of better quality.

I think most MSX computers only have a single layer PCB, so de-soldering and re-soldering components is not that difficult. As long as you set the temperature of your iron not to high, and don't hold it in the same place to long, or your traces will peal of (some experience is required I guess).

In general it's a good idea to replace electrolytic capacitors in old equipment, if that equipment is still used (if only for looking @, no point in replacing elco's).

Of course the "If it's not broken, don't fix it" is strong here. Only a small % of the population is comfortable with a soldering iron, aware of ESD risks etc. So having an 'idiot' try to replace any component, is riskier than leave something in place that's old, but not causing trouble (yet).

What's old for an elco? 5 years? 10 years? 20 years? Also depends a lot on operating temperature, # of hours it has run, function in the circuit, manufacturer / series / perhaps even particular batches, etc, etc. Through hole <-> SMD is irrelevant, but of course there will be technology differences between those (good luck finding SMD elco's in MSX machines, btw ).

Usually I wait until a machine needs to be opened up for some reason. At that point, the older an elco is, the bigger my suspicion it has negative influence somehow (disturbances on screen etc), the quicker I'd replace it. If <10 years old & not causing trouble, I need a good reason. If >10 years old & suspect somehow, no reason needed.

But it depends on equipment. I have an old (+/- 13 year) CRT here that's still used, which would probably benefit from replacement of electrolytic capacitors inside. Which I don't: because for this old CRT, it's also not worth the expense+effort.

In many cases a bad (but not 100% failing) capacitor won't prevent an MSX from booting, just degrade some signal (eg. sound / video output). Those in the power supply would, but these have very wide safety margin, so the machine might still work if a capacitor has 5x the leakage current, and lost 2/3 of its brand new capacity. And the linear power supply you find in most MSX'es is much easier on capacitors than modern switching power supplies.

And most MSX machines will be used only now & then, or stored in boxes most of the time. Unlike TV's, PC's etc which many people leave powered on on all the time (beside routers, modems, network switches, set top boxes etc).

So a combination of factors making that most will last long. But 25 years is respectable age for an electrolytic capacitor. For original MSX machines still in use, I'd expect elco-related problems to increase in the next 5-10 years or so.

I also heard somewhere that these caps have certain life-span that is usually measured in hours and the same cap could last longer with temp of 85C than with 125C. I am not sure but do the dielectric fluid inside the caps get dried-up after the life-span? I was also told that it isn't a good idea to keep capacitors without applying voltage drop across it otherwise oxidization takes place. The caps I have seen do have the manufactured date and with a piece of paper, pen and a calculator; you could easily figure out if it’s time to replace the cap. So in the end, I do agree that it’s better to replace them after certain time.