Replacing a MSX Power Supply (for beginners...)

Rookie (19)

13-05-2015, 12:40

Hi. Inspired by some other MSX users, I decided to give a nice clean to one of my oldest and most unused MSX machines: the Sony HB-F9S. I carefully disassembled it and as expected, I found lots of dust and dirt inside so I proceeded with the cleaning process.

Then I realized the PSU was in a pretty bad shape and I was wondering how hard would be to find a replacement and do the change. I am a complete beginner in electronics so I thought it would be a nice project for me to get more into it and learn something new.

What do you guys think?
- Is it worth to try to replace it even if the computer is actually working fine?
- Is it possible to find a modern PSU with the needed electrical specs that fits in the case?
- Being a beginner... maybe better leave it as it is?

I looked through the service manual and found what seems to be the schematics for my power needs.

Thanks.

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Par NYYRIKKI

Enlighted (6010)

13-05-2015, 15:49

xesco wrote:

- Is it worth to try to replace it even if the computer is actually working fine?

I would not, but this is a hobby for all of us. Sometimes we make things that are not worth it.

Quote:

- Is it possible to find a modern PSU with the needed electrical specs that fits in the case?

Yes, but the prices many times might be higher or equal to geting a new MSX. I've been also thinking this, but it is kind of hard to find small and powerfull enough PSU for reasonable price. One option is to use some old laptop PSU and ie. PicoPSU (look from google)

Quote:

- Being a beginner... maybe better leave it as it is?

Modifying anything that has high voltage input is not recommended as a beginner project. There is always a risk of injury and big damage to hardware.

Par Jipe

Paragon (1586)

13-05-2015, 16:31

Quote:

always a risk of injury and big damage to hardware

and also big damage for human

Par RetroTechie

Paragon (1563)

14-05-2015, 02:01

It's easy to find AC -> 5V or AC -> 12V modules these days that are cheap, small and powerful enough. Problem is you need multiple supply voltages, so you'd need multiple ones of such modules. Or add in a few DC-DC converters. Or find a power supply that is small enough & outputs all needed voltages. And then you'd still keep some of the mains AC parts (fuse/switch/line filter). Read: not for beginners.

Also such a psu may well be of lower quality than that older, less efficient one you have.

NYYRIKKI wrote:

Modifying anything that has high voltage input is not recommended as a beginner project.

+ many. With electrical safety, you HAVE TO KNOW WHAT YOU ARE DOING, PERIOD. Especially since you may not be the only user of that machine.

Personally I'd say that power supply looks fine... what you're looking at is dust & a bit of crumbled epoxy, all pretty normal. If you're going to change anything: consider replacing those big electrolytic capacitors (in the middle of the cooling plate). And perhaps the smaller ones too.

And: remove that RTC battery before it leaks & nukes pcb tracks. Probably you can simply cut it out so you don't need to disassemble the main board.

Par Grauw

Ascended (10678)

14-05-2015, 14:16

Yeah, battery & caps are a good and useful starter project. I should probably replace the caps on my turboR as well… I see vertical bars in the RGB output, one pixel or so apart, where the output of my CX5MII is completely smooth and sharp.

Par xesco

Rookie (19)

15-05-2015, 09:03

Thanks to all for your feedback!

So I guess there's no such a thing as "Replacing a PSU for begginers" Fair enough, at least now I know. But I like your ideas of a good starting projects with this machine.

Quote:

Personally I'd say that power supply looks fine... what you're looking at is dust & a bit of crumbled epoxy, all pretty normal

Then, I would just put it back as it is. I did not know that was normal. Thanks.

Quote:

consider replacing those big electrolytic capacitors (in the middle of the cooling plate). And perhaps the smaller ones too.

Ok, I will think about that. What is the main reason behind this change? I do have a soldering station, and I have been learning how to use it and I made some cables and stuff. But I have never used it in a real working board...

Quote:

And: remove that RTC battery before it leaks & nukes pcb tracks. Probably you can simply cut it out so you don't need to disassemble the main board.

Sure, I can cut it out. But, do I need a replacement? The battery only powers the date/time as far as I know, but still it would be nice to have one...

Thanks!

Par Grauw

Ascended (10678)

15-05-2015, 14:12

Electrolytic capacitors (the cylindrical ones) have fluid inside that can dry out or leak when they get older. This diminishes the functioning of the capacitors and is often the cause for functional problems like video display issues, and if they leak it can also damage the main board.

Especially caps produced between 1999 and 2007 have known faults, but because the caps in MSX computers are by now 30 years old, it’s a good idea to replace them. It solved problems for various people here on the forum. So it’s both a useful precaution as well as a good starter project.

Par xesco

Rookie (19)

16-05-2015, 13:23

Ok. I will do my research on what capacitors to use for the replacements. Meanwhile, continuing with my restoration and cleaning process...