NEC PC-98 stuff

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NEC PC-98 stuff

Post by kana85hz2c »

Hey guys, I'm a guy from Japan who recently got hooked super hard on retro hardware.

It seems retro stuff in general just seems to be booming here nowadays, with OG gameboys reaching pretty absurd prices, even the junk second hand stuff.

Basically, while there seems to be a huge demand for the nintendos and segas and playstations and what not, PC98s haven't seen a ton of spotlight just yet.
For those of you who have never heard of a PC98, they're basically one of a bunch of Japanese only DOS-era PCs that were born because the western stuff didn't have support for Kanji.
Some of these japanese only PCs include the PC88, X68000, FM Towns, MSX etc.
They are kinda well known for having a huge library of hentai games, but there's a bunch of games that have made it big that have their roots on the PC98, such as Touhou project, the Y's series, and the company Compile in general.
These PC98 games have an aesthetic you can't really find anywhere else. I'd call it the vaporwave nerd's wet dream.
eda1cfa516f8854eedf2e11d94a4cd8d.jpg
Audio-wise they also have a Yamaha chip that sounds pretty damn awesome.

You can still pick up (somewhat) working PC98s for pretty cheap, and there's a fair bit of documentation in Japanese for the niche market it has here.
Even the broken ones seem to be a few leaky capacitors away from perfect working conditions. Huge surprise.
The hardest part of getting one of these systems is the keyboard and mouse setup, because they use proprietary plugs and a USB converter will set you back quite a bit. I've seen a keyboard with missing keys for pretty cheap at our favourite Hard Off so maybe that's something to go off of.

I've been considering picking one up myself to play around with, and maybe translate some of the Japanese info into English so hopefully it can gather some attention overseas.
My biggest concern is that since these PCs were only produced domestically, it'd be rather difficult for non-Japanese speakers to really enjoy what it has to offer.
I could definitely translate the games into English, and that would be a pretty cool project but since I work as a designer my programming skills are limited to basically nothing, so all this DOS stuff is greek to me and I'm not even sure what other kind of cool stuff you could pull off with these computers.

There's an emulator you can use to see what it's like for yourself, but it's kind of a nightmare to setup because you need the actual BIOS from one of these machines and they aren't really lying around on the internet either.

Is anyone here interested in these computers at all? Would be nice to be able to discuss these super old PCs and what kind of ideas people had for them.
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Re: NEC PC-98 stuff

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Heh it's funny you bring this up, I've also had a small fascination with the PC-98 for a while. It mostly started because I was interested in the original release of Policenauts (before the art was redone by AIC) - as you say, there's something about that 640x480 pixel art aesthetic (and no, I'm not interested in the hentai lol)

Likewise I've also really liked the idea of being able to get the games translated and introducing them to a wider audience. But while my game modding abilities have steadily progressed, unfortunately (like most weebs who say they're going to learn Japanese), my proficiency with the language has never gotten to a point of comfortably being able to read it.

Outside of that small fascination, I don't have a whole lot of knowledge. Are there any games you think would be particularly interesting to translate? I think you're right that emulators are gonna be the primary way people outside of Japan will be able to play these, the hardware is just too obscure/difficult to acquire otherwise. Though maybe I should try tracking one down next time I go...
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Re: NEC PC-98 stuff

Post by kana85hz2c »

I do have a couple of games that could be interesting to look into:

One being 魔導物語(Madou Monogatari), which if you've heard of Puyo Puyo, is the prequel to it. It's a dungeon crawler RPG and you may recognise a lot of the characters if you've ever played Puyo Puyo.
Puyo Puyo itself started on these old DOS machines too, so there's quite a bit of content out there.
Despite getting a very modern sequel in 2013 I haven't seen much talk of Madou Monogatari outside of Japan, but I think that the connection it has with a game that's now rather well known even outside of Japan might make it interesting to look into.


Another game that could be worth looking into is the POWER DoLLS series.
It's a mecha turned based strategy game by Kogado, and did well enough to get sequels well into the early 2000's, even after the era of PC98s.
The aesthetics are there, and legend has it that the gameplay was so difficult that a lot of the people who got lured in by the designs got absolutely pummeled.
There technically have been remakes of the earlier versions for the XP and what not, but like you say with Policenauts there's just something about that original look that just makes it nice.

The soundtrack by the way is an absolute banger.

There's a lot of other games like Brandish, YU-NO, Y's etc as well that seem to be somewhat recognised out of Japan as well, but they all have modern and/or English ports so... yeah.
There's a neat database of what seems to be most of the games for the platform on refuge.tokyo, so that might be worth looking at, although you'd have to wade through a cesspool of hentai games...

If you were actually interested in getting the actual hardware I could probably help with that too lol. I did have a mate back in Australia who wanted one so I was looking into getting my hands on the laptop versions too.
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Re: NEC PC-98 stuff

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kana85hz2c wrote: Wed Dec 14, 2022 5:10 am One being 魔導物語(Madou Monogatari), which if you've heard of Puyo Puyo, is the prequel to it. It's a dungeon crawler RPG and you may recognise a lot of the characters if you've ever played Puyo Puyo.
Puyo Puyo the tile-matching game? I never would have expected a dungeon crawler to lead into a puzzle game lol
kana85hz2c wrote: Wed Dec 14, 2022 5:10 am Another game that could be worth looking into is the POWER DoLLS series.
It's a mecha turned based strategy game by Kogado, and did well enough to get sequels well into the early 2000's, even after the era of PC98s.
The aesthetics are there, and legend has it that the gameplay was so difficult that a lot of the people who got lured in by the designs got absolutely pummeled.
It's so interesting to see games like these. Usually when I see a game that was released in the West, I have some frame of reference for it, but this is like a whole other world that I have no awareness of. I'm not even a big anime person, but the art styles really fascinate me. Are there any action games like side-scrollers/platformers or is it mostly point-and-click? (I guess PC games in the West were mostly point-and-click in that era so that would make sense)

I'll definitely check out refuge.tokyo (I like the website design already lol). Sorry for the late reply, I'm a little busy right now trying to finish some stuff before the holidays, but after that I should have a lot more time to look at stuff like this.
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Re: NEC PC-98 stuff

Post by flatrute »

Unrelated but I like one of the quirks of MS-DOS and Windows on the platform that the drive OS resides in is assigned letter A whether or not it is a floppy or a hard disk. I like it so much so I tried to replicate that during one of my Windows reinstallation and it somehow worked (aside from system pagefile refused to be made which in turn made OOM killer kicked in every time I open more than 10 programs or something pepeLaugh).

Edit: A space espaced but I managed to catch it and put it in its place.
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Re: NEC PC-98 stuff

Post by kana85hz2c »

MattKC wrote: Mon Dec 19, 2022 4:59 pm Puyo Puyo the tile-matching game? I never would have expected a dungeon crawler to lead into a puzzle game lol
Yeah man better add that to the list of spin-offs that sold more than the original series haha
MattKC wrote: Mon Dec 19, 2022 4:59 pm It's so interesting to see games like these. Usually when I see a game that was released in the West, I have some frame of reference for it, but this is like a whole other world that I have no awareness of. I'm not even a big anime person, but the art styles really fascinate me. Are there any action games like side-scrollers/platformers or is it mostly point-and-click? (I guess PC games in the West were mostly point-and-click in that era so that would make sense)

I'll definitely check out refuge.tokyo (I like the website design already lol). Sorry for the late reply, I'm a little busy right now trying to finish some stuff before the holidays, but after that I should have a lot more time to look at stuff like this.
The whole genre of Touhou-style shooting action games have their roots here too so I'm sure there's an endless amount of different games to look through.
Every time I hop by the 2nd hand stores and check out their PC98 I always find games with some amazing box art that I've never even heard of. (although the catch is that usually they're R18)
I've been a bit busy myself over the new years so don't worry lol.
flatrute wrote: Mon Dec 19, 2022 6:37 pm Unrelated but I like one of the quirks of MS-DOS and Windows on the platform that the drive OS resides in is assigned letter A whether or not it is a floppy or a hard disk. I like it so much so I tried to replicate that during one of my Windows reinstallation and it somehow worked (aside from system pagefile refused to be made which in turn made OOM killer kicked in every time I open more than 10 programs or something pepeLaugh).
I think many years ago when I was trying to get XP installed on something it wasn't meant be on, it installed itself on the drive A and immediately began to poop its pants lmao.

=====

So I managed to find a decent deal on a PC-9821Ap/M2 just today and grabbed it without thinking too much.
Image
I didn't read the description properly before bidding because apparently it fails to read the "disk".
Fingers crossed it's just the floppy drive that's gone beached and not the HDD IDE controller, but once this and the keyboard/mouse and monitor I have yet to source arrive, I'll just use this thread to log my attempts at getting it to work. (although I may have to move the thread to the Hardware section?)

The PC-9821Ap is apparently the holy grail of PC-98 gamers mainly because it's got the sweet sweet Yamaha audio chip pre-installed, has newer hardware in general but still supports older(and more common) expansion cards I think?
It's also apparently the first PC98 to support Windows 95 so that might be a fun thing to try out.
If it is just the floppy being dead I could just copy the DOS images and everything I need onto a CF card and just convert that to IDE hopefully negating any need for the drive.
If all goes to plan that's some 5000 yen well spent honestly.
If the IDE doesn't read it's gonna be one hell of a project lol because god knows how the motherboard works on this.
Image

EDIT: Actually yeah Matt now that the hardware modding category is called just hardware now maybe could you move the thread over? Or can I do it myself? Haven't used one of these forums in years
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Re: NEC PC-98 stuff

Post by flatrute »

kana85hz2c wrote: Sat Jan 07, 2023 5:42 pm EDIT: Actually yeah Matt now that the hardware modding category is called just hardware now maybe could you move the thread over? Or can I do it myself? Haven't used one of these forums in years
You can simply split the lower half into a separate post.
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Re: NEC PC-98 stuff

Post by kana85hz2c »

flatrute wrote: Sun Jan 08, 2023 1:49 am You can simply split the lower half into a separate post.
Fair enough, will do that when I start writing up the logs properly.
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Re: NEC PC-98 stuff

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kana85hz2c wrote: Sat Jan 07, 2023 5:42 pm EDIT: Actually yeah Matt now that the hardware modding category is called just hardware now maybe could you move the thread over? Or can I do it myself? Haven't used one of these forums in years
Yeah I may as well move this to "Hardware", it probably does make more sense there.
kana85hz2c wrote: Sat Jan 07, 2023 5:42 pm The whole genre of Touhou-style shooting action games have their roots here too so I'm sure there's an endless amount of different games to look through.
Ahh I forgot about Touhou, good point. I'd love to get more into the PC-98 scene.
kana85hz2c wrote: Sat Jan 07, 2023 5:42 pm So I managed to find a decent deal on a PC-9821Ap/M2 just today and grabbed it without thinking too much.
Nice haul! Hope you can get it fixed. For 5000 yen that seems like a steal. There are early versions of Windows for these too aren't there? That could be interesting to check out...

(Also not to be pedantic, but could you repost your images as post attachments on the forum? It's preferred here in case other websites/image hosts happen to go down in the future)
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Re: NEC PC-98 stuff

Post by kana85hz2c »

Sorry about the images and thanks for the category move :)
MattKC wrote: Mon Jan 09, 2023 5:23 am Nice haul! Hope you can get it fixed. For 5000 yen that seems like a steal. There are early versions of Windows for these too aren't there? That could be interesting to check out...
Apparently these Ap models were designed with Windows 3.1 in mind, but a year later were re-released for Windows 95.
Comparing the specs between the newer ones and the non-W versions, I don't think there's any differences other than the extended memory.

Running windows on these machines sounds like an interesting topic, especially since the whole point these existed were for their Kanji chips and DOS not having support for Japanese text, which should've been solved somewhere around this era.(By software fonts)
Some quick research tells me there was a different build for each type of PC running Windows 3.1, but apparently there's no visible difference between Win95 running on a PC-98 or a IBM compatible DOS/V machine apart from a different IME.

I'd love to see what I can do to try out Windows but once again it seems the CD-ROM is proprietary af so I might just have a poke at it with an emulator. Apparently you can even get Windows ME working on them.
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Re: NEC PC-98 stuff

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kana85hz2c wrote: Mon Jan 09, 2023 7:31 pm there's no visible difference between Win95 running on a PC-98 or a IBM compatible DOS/V machine apart from a different IME.
That is interesting. Could there be simply due the differences between the keyboard layout of two platforms? I have not clicked the link Clueless
kana85hz2c wrote: Mon Jan 09, 2023 7:31 pm I'd love to see what I can do to try out Windows but once again it seems the CD-ROM is proprietary af so I might just have a poke at it with an emulator. Apparently you can even get Windows ME working on them.
Windows 2000 and ME are the last versions to support the platform. I wonder how many copies of each were sold...
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Re: NEC PC-98 stuff

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flatrute wrote: Tue Jan 10, 2023 1:11 am That is interesting. Could there be simply due the differences between the keyboard layout of two platforms? I have not clicked the link Clueless
Yeah so the PC98's keyboard layout was easier to switch between Japanese inputs, but it got phased out over the 106/109 Key layout that you now find all over Japanese PCs.
flatrute wrote: Tue Jan 10, 2023 1:11 am Windows 2000 and ME are the last versions to support the platform. I wonder how many copies of each were sold...
I tend to believe the PC market never took off here as much as it did overseas, so not a whole lot I imagine...
The whole reason there weren't ports of big Nintendo or Sega games onto PCs (apart from the licensing hell) is that there wasn't much demand for it.
I've been talking to a bunch of people who should've been in their 20s during the age of PC98~WindowsME but every single one of them bought their first ever PC only after XP came out.
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Re: NEC PC-98 stuff

Post by kana85hz2c »

So an update on the PC98 that I ended up buying:

It's arrived at my place now. Placed a Steam deck on top for comparison and it's interesting seeing two computers about 30 years apart in terms of technology on top of each other.
FmQ7DXCacAAOP6q.jpg
I haven't had the chance to open it up just yet and if I can't make the time this weekend I suspect I won't until next weekend-ish...
However I did manage to get in contact with the seller who told me that it was indeed the floppy drives that are dead, and that they didn't even bother testing if the IDE works or not.

I had read somewhere that the Ap models had a variant with a CD-ROM and indeed the case seems to have what seems to be a CD-ROM slot, so if I'm lucky I might get that to work out.
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Re: NEC PC-98 stuff

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kana85hz2c wrote: Fri Jan 13, 2023 6:34 pm However I did manage to get in contact with the seller who told me that it was indeed the floppy drives that are dead, and that they didn't even bother testing if the IDE works or not.
I guess it's not unsurprising, any "moving parts" devices this old are probably very liable to break. Hopefully the IDE works - I'm also wondering if any of those various floppy drive emulators could be used if not.
kana85hz2c wrote: Fri Jan 13, 2023 6:34 pm I had read somewhere that the Ap models had a variant with a CD-ROM and indeed the case seems to have what seems to be a CD-ROM slot, so if I'm lucky I might get that to work out.
Ooh CD-ROM could be good. Again my only real reference point is Policenauts, but I know that was a CD-ROM game.
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Re: NEC PC-98 stuff

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MattKC wrote: Sun Jan 22, 2023 8:12 am Ooh CD-ROM could be good. Again my only real reference point is Policenauts, but I know that was a CD-ROM game.
90% of the games I'm interested are in either 3.5" Floppy or CD so I guess whichever I find cheaper and quicker wins the race!

So today I set out on an adventure to get this PC up and running, and spoilers: it didn't go well.
I'll leave everything I did as a log here so here's your warning that this is going to be a loooong post.
Also I couldn't attach videos so I'm linking relevant posts I posted on Twitter while this was all going on.

First I had to find a Mouse and Keyboard. Funnily enough these things cost more than the damn pc lol.
But I did manage to grab one that wasn't technically for the PC98, but EPSON's clone PC98: the PC-486.
They use the same ports and same encoding so no adapters were necessary and it worked right out of the box.

I also ordered a 512mb CF card, which was also unnecessarily expensive, and also compulsory in this situation as the BIOS does not support anything bigger than 540MB.
I used this guide to install my copy of YAHDI(basically an image of a PC98 hard drive with DOS 6.2, a bunch of basic tools and a few games to top it all off) to the CF card, and off we were to the races.
I should note at this point that I had a friend over to watch this all happen, and if it weren't for him I wouldn't have gotten so much done in one day.
20230122_151951.jpg
With the sound of the iconic PC98 boot-up beep sound, I found myself already inside DOS and everything was working fine.
I could even get games to run. And boy did I enjoy the sweet sweet YM2608 sound coming right out of a 30 year old speaker.
20230122_152656.jpg
I was having the time of my life. Touhou games I only watched on youtube were now playable, and not at the choppy 10fps that my emulator poops out.
(BTW if you've noticed how the edge of my monitor is absolutely munted, it's because I just picked up a random 880 yen junk monitor at a hard-off, and not the fault of the PC.)

The fun slowly started to fade away when I started noticing a few quirks popping up gradually.
The first one being almost hillarious was that the computer's clock was going apeshit crazy.
This wasn't as much of a concern for me and eventually once I set the time manually on DOS it fixed itself.

The latter problem was much more of an issue:
I started noticing really bad static buzzes happening sporadically.
Initially I assumed it was either because 1) the volume was maxed out and I was clipping the wub wub bass, or 2) my friend's phone was right next to the speakers, and the 5G signals were causing noise to happen in the circuit
We soon realised it was neither, and the noise was just getting worse.
And then it got bad. Really bad.
Fwiw through all of this everything apart from the audio worked perfectly.

I was reading up on leaky capacitors during my research prior to everything arriving, and noted that the 98 Mate series up to the 3rd gen used capacitors known to leak all over and cause problems.
Googling once again gave me quite a bit of information.
Firstly when designing the 98 Mate series, NEC cheaped out on the capacitors using cheapo surface mount electrolytics that leaked everywhere.
In the first gen 98 Mates, which is mine, the leaky capacitors most often cause problems with audio. (and the floppy boards also had these bad capacitors)
20230122_161618.jpg
20230122_161248.jpg
Upon closer investigation yes the capacitors looked liked they were at least starting to leak, and since the described problems matched what I was seeing exactly, I ran out my door to take the train to Akihabara, where I bought myself tantalum capacitors to replace the leaky caps.

I also found two articles, the latter matching my exact model talking about how they had the same audio issues, and just replacing the caps failed to resolve the issue.
They referred to a "special move" they used to eventually fix their computers.
That was to literally wash the entire motherboard with water.
They claimed that it would wash away any residue of the leaky capacitors, for which it was mandatory that I used an alkaline detergent.

Everything about washing the motherboard with water rings alarms in my head, so I prayed and prayed as my friend soldered the new caps on for me(yeah I was too scared to solder surface mount components).
Halfway through, after replacing the ones that looked the worst, we turned on the power and were amazed to see the issue resolved.
Until it didn't.
It lasted about 3 minutes before the noise came back, even worse than before.
Saddened, we pulled it apart again and replaced the rest of the caps.

After all the caps were replaced, we put the bare minimum parts back together and really wished for a miracle while we turned the power on.
Once again, it seemed to work fine, until about 1 minute later when turned into absolute noise gunk.
No amount of playing around with configs and drivers and CPU clocking helped.
So with all other hope gone, I did the unthinkable, and after letting it sit around to discharge for a while I washed it in my kitchen sink.
20230122_234411.jpg
So that's where we're at. It's drying under my air conditioner, and I will give it another shot in the morning, but I'm honestly out of ideas for the rather big possibility that it doesn't.

Here's where my thinking is at right now:
1) The issue creeps up over time, rather than being a sudden thing, so it must be capacitor related.
2) I used tantalum capacitors rather than electrolytics because they would last longer. A blog post from a guy who literally repairs these for a living recommended the tantalums, but only after buying radial tantalum caps did I realise he recommended the chip type caps with a built-in fuse. Does that mean my choice of capacitors was bad? Asking on twitter I was told that some people think electrolytics should only be replaced with electrolytics, and some people even go for identical capacitors that haven't leaked yet.
3) The issue seems to be localised entirely within the audio section of the motherboard. Or at least I haven't noticed anything sussy apart from the audio. So it could be some of the other caps that technically weren't affected by the plague but could still have leaked/broken.
4) By the time I washed the motherboard, the noise issue turned far worse, initially just flat out having the bass and rhythm tracks not play at all, and eventually I couldn't get sound from neither the speaker nor headphones. Letting it sit for a bit and then restarting got the speaker working once again for an instant before it died again.
5) Holy shit there's a lack of info out there for these. Even generationally they seem to redesign the entire system so info about my specific motherboard is super limited. But at the same time apparently the Ap2 series, that has the same issues has a whopping 65 capacitors vs the 17 on mine so thank god I didn't get one of those.

Given the whole reason I bought a physical PC98 was so I could enjoy its audio, it's a huge bummer that I can't get it to work and if anyone else has any ideas I would greatly appreciate them.

EDIT: Doing some more reading after posting this, I think I have 2(maybe 3) ideas in case washing doesn't help.
This article mentions 2 things that worry me: 1) radial lead capacitors may have a different impedance that could affect the computer, and 2) the writer, though never having more than very slight noise mixed in with the audio at max volume, had to replace all the other caps that I left alone today, in order to get rid of that slight noise. This post also notes that bad capacitors have also been known to screw up the clock, so that's also food for thought.
The article that suggested I wash the motherboard also mentioned that if washing doesn't solve the problem, I should inspect the 12V rail from the PSU. In fact, I did notice incredible coil whine from the PSU but never really wanted to pull it apart for obvious reasons, but there are reports that the electrolytic capacitors inside could leak all over the place and damage the voltage regulator.

...and I just realised that this feels like I'm inside Matt's PS3 video.

On a more positive note, here's some pictures I took of the insides while I was pulling it apart.
20230122_145513.jpg
The CPU is actually attached on a daughterboard, which reminds me of the Pentium 2. Apparently it's thanks to this design that a leaky capacitor doesn't straight up just brick the whole system.
20230122_145942.jpg
20230122_145950.jpg
Add-on RAM is also done via a daughterboard. This specific one has a whopping 14MB of RAM.
20230122_215037.jpg
These are the plagued capacitors. I didn't see any visible leakage except for some corrosion on some of the legs.

Also, I recently found about a manga called 16-bit Sensation.
817vtDnchRL.jpg
It is quite literally a manga about gamedev for PC98s back in the early 90s, loosely based off the lives of Amatsuyu Tatsuki, and Mitsumi Misato, who are known for their artwork at AQUAPLUS with famous titles like ToHeart2, and Utawaremono.
To top it all off the manga is drawn by the mangaka who did the The World God Only Knows series, and was apparently a big enough hit that an anime adaptation got confirmed at the end of last year.
Knowing anime nerds it's going to be a matter of time before people who watch the show will start looking for a PC98 to own themselves, so I feel it's especially important to leave some English info out there.
I'm not sure there's English translations out there but if there are, I would very much suggest you give it a read, even if you're not into the whole weeb stuff.(if there aren't I might just do it myself)
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Re: NEC PC-98 stuff

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kana85hz2c wrote: Sun Jan 22, 2023 3:56 pm Also, I recently found about a manga called 16-bit Sensation.
817vtDnchRL.jpg
It is quite literally a manga about gamedev for PC98s back in the early 90s, loosely based off the lives of Amatsuyu Tatsuki, and Mitsumi Misato, who are known for their artwork at AQUAPLUS with famous titles like ToHeart2, and Utawaremono.
To top it all off the manga is drawn by the mangaka who did the The World God Only Knows series, and was apparently a big enough hit that an anime adaptation got confirmed at the end of last year.
Knowing anime nerds it's going to be a matter of time before people who watch the show will start looking for a PC98 to own themselves, so I feel it's especially important to leave some English info out there.
I'm not sure there's English translations out there but if there are, I would very much suggest you give it a read, even if you're not into the whole weeb stuff.(if there aren't I might just do it myself)
Therefore I torrented 2 raw scans of it LULW and brute force the manga by the power of Jisho and Google Input Tools pepeLaugh (I downgraded my OS to Windows Server 2019 which is still not FreeBSD but it runs faster so Stare)
16bitセンセーション.png
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Re: NEC PC-98 stuff

Post by kana85hz2c »

flatrute wrote: Sun Jan 22, 2023 5:13 pm Therefore I torrented 2 raw scans of it LULW and brute force the manga by the power of Jisho and Google Input Tools pepeLaugh (I downgraded my OS to Windows Server 2019 which is still not FreeBSD but it runs faster so Stare)
mah man. I wonder if all the 90s internet memes will translate well on Google and Jisho but fingers crossed?

Anyway it's a new day and after checking with a piece of paper that the motherboard is completely dry I plugged it in again.
It worked! For about 5 minutes.

My next bet was the PSU, so time to take it apart. And boy is it filthy.
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I gave it a quick blow with compressed air and that's where we are right now.
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I can't see any obvious leaks, and the 12V rail is definitely giving out 12V.
kana85hz2c
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Joined: Tue Dec 13, 2022 3:10 pm
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Re: NEC PC-98 stuff

Post by kana85hz2c »

End of Day 2 at my attempt to repair this thing?

God this is such an emotional rollercoaster.

Upon closer inspection of the PSU I noticed that the caps were indeed leaking.
The intense noise that I assumed was coil whine also made sense now.
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Off I went to Akihabara again (btw each ride back and forth is about 1.5hr of travel and 1100 Yen)

I got my capacitors,
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Found a Sega Saturn sitting around,
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and once I got back home I immediately started soldering.
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Yeah these mofos are definitely leaking.

I replaced all the caps that I could(I left out the 200V 100uF cap out on purpose assuming something that massive wouldn't leak, and visible inspection led me to believe it was alright)
and promptly realised I completely missed a capacitor when I memoed which ones I needed.
Regardless I prayed it wasn't relevant, and turned on the PC.

It passed the smoke test(at this point I'm more surprised I haven't managed to screw anything up) and I could immediately notice the sound, or lack thereof, coming from the PSU.
The audio also seemed fine? I was so sure I had achieved victory at this point, but just as I was about to do my little victory dance the noise started to come back.

I'm honestly one step away from getting stuck at this point.
I could replace the capacitor I forgot to get in the PSU, but I feel like it wont help.

There's just one place where there's a ton of capacitors, all electrolytic, most likely related to my issue, but such an obvious pain I didn't want to think about it.
It's the audio circuitry.

As I mentioned earlier, the sound is based off the Yamaha YM2608 chip, which normally is on an add-on board, but on the 98 Mate series, are built into the motherboard.
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There's also a daughterboard that attaches near it, and all I could find online was that it's the sub-system for the audio.
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The green stuff with the red dots are all capacitors.
Now these aren't known to fail, but at this point I just can't think of anything else.

Before committing myself to soldering 60 or so capacitors my one last copium attempt will be to replace earlier mentioned PSU cap, as well as one on the daughterboard that looks like it's slightly bulging.
20230124_010022.jpg

And here I thought this was just going to be a floppy repair thread.
kana85hz2c
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Joined: Tue Dec 13, 2022 3:10 pm
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Re: NEC PC-98 stuff

Post by kana85hz2c »

At this point I'm just going to resolder every single capacitor on these boards, and for future reference I'll leave my shopping list here.
スクリーンショット 2023-01-24 135113.png
kana85hz2c
Posts: 26
Joined: Tue Dec 13, 2022 3:10 pm
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Re: NEC PC-98 stuff

Post by kana85hz2c »

Super happy to announce: she's fixed!

This thread is starting to look more like a thesis so I'll try to keep it short.
Basically I bought all 79 caps and started to contemplate life while replacing the caps from the motherboard and DAC.
I thought through-hole would be easy to solder but apparently not on a 6+layer PCB...
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At one point I thought to replace that one cap that I forgot to buy for the PSU, and once I did, voila, the clock fixed itself.
This led me to believe maybe something else on the PSU may have been borked, and after some more research online I found a 5ch thread where a guy said that the heat from the voltage regulators broke a resistor in his PSU, leading to the +12V rail outputting something more like +5V, causing audio issues and HDD/FDD malfunction.
This rang all sorts of bells, and upon inspection the said resistor was definitely broken, giving me infinite ohms of resistance(basically turning it into an open circuit)
It also looked super burnt and smelled really bad
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so after getting a replacement resistor, soldering it on and pressing the power button, I was most pleased to see the issue completely fixed.
I gave the floppy a go too, and put in a 5.25" floppy hentai game, but initially that didn't work.
I could see files in it but couldnt open or copy any of them.
I found a way of opening one of them in a text editor, and lo and behold the files were for the Sharp X68000 and not the PC98.
Unfortunately that means I don't have a way to 100% check if the FDD works, but if I can open some of the files at least on a text editor, I'm going to assume that it works.

So that's the end of the repair journey!
If anyone ends up getting an A-Mate and ends up with similar problems I would suggest the following:
1) Replace all the SMD caps on the motherboard
2) Replace all the caps on the PSU
3) If the problem persists, check the R53 resistor on the PSU

Now time to enjoy my games and be on the lookout for any CD drives and/or 3.5" FDDs...
Last edited by kana85hz2c on Fri Jan 27, 2023 7:23 am, edited 1 time in total.
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