I could not resolve keeping my MSX2 yellow. No way! All the more, the design and look & feel of the computer was part of my purchase choice. To me, the HB-F500F was white and crème in my memory, not yellow. I therefore decided to attempt retro-brightening the computer and floppy drive faceplates, the keyboard enclosure and all the yellowed keys. If you are not familiar with RetrObright, it is a chemical process to revert the transformation that happened over time in some plastics. It is the fire-retardant additives (bromide) used by the manufacturers that reacts over time with the UV rays and turn the plastic more or less yellow. This technique is a reversal not a cure, which means that a retro-brighten plastic will yellow again if exposed to UVs.
The process is simple: clean thoroughly your yellowed plastics and wait for a sunny and hot day. When you see the sun – yes, in some places, we don’t see it very often – use a cream developer (40 volume or ~12% hydrogen peroxide) and apply it all over the plastics. This is the cream used in salons. Put small items in a clear bag (floppy faceplate, keys) and use food wrapping film for bigger items (computer faceplate, keyboard housing). The goal is to avoid that the mixture dries out. Expose bags and wraps to as much sunlight as possible and wait. Attention, temperature is as important as the hydrogen peroxide, so favor a hot day for your RetrObrigh session. In my case, the treated parts’ surfaces reached up to 67C, and after a couple of hours, the cream (a gel in fact) liquefied! It is important to stay alert so you can stop the process at the right time. And the right time is when the part brightens up to your expectations. I used the back side of the pieces as a reference since they kept their original tint. This way, I removed the parts as soon as I found them ready, limiting the risk of overbleaching the plastics. In addition of the usual precautions when using hazardous chemicals (that may become quite hot), take a special care when rinsing the parts with water. Otherwise the plastics may fade more than expected (and show ugly marks – I made that mistake). RetrObright is an empiric method and there are no guaranties that it will work, and even if it works, that it will do the way you expect. So, use it at your own risks. In my case, it worked as a charm. In less than three hours, my HB-F500F returned to its original state!