CPU upgrade options for 20F

[kamiboy]

So, I hopefully, if the seller does not decide to screw me over, have a 20F with faulty PSU on the way to me. Assuming it survives the shipping ordeal, and the fault can actually be fixed, I'd like to maybe upgrade the CPU while I have the insides spilled out on the floor.

Anyone know which CPU's are drop-in replacements for the 386 in the 20F?

[famiac]

You can get a Cyrix 486.
I would recommend socketing the CPU.
Also you might want to get some chip quik because the CPU is a real pain to desolder, even with a Hakko FR300

[kamiboy]

Are you referring to the Cyrix 486DLC processors? Will any of them do? They come in various clock speeds.

Are they plug and play replacements are will additional components, like the crystal need to be swapped as well?

[SuperDeadite]

Some models of Towns actually do have socketed CPUs, my old Model 1 2H did.  All the ''Towns II'' machines are soldered though.  If you use a Cyrix you will need to change the crystal too, and be sure to add a socket for that, as a lot of games do not work properly at 486 speeds.  (Official 486 and Pentium Towns machines can run at proper 386 speeds for compatibility).

[kamiboy]

You make it sound like there are CPU replacements that do not require a new crystal, if so I am curious to hear which.

But to be honest hearing that this might cause compatibility problems has killed much of my enthusiasm for the upgrade route. Any notable titles negatively affected by an 486 upgrade?

[SuperDeadite]

Quite sure any CPU upgrade in that unit will also need a crystal swap.

But yeah, quite a few games will only work in 386 mode, however there are many games where 486 is highly recommended or flat out required.  Galaxy Force II on a 386 runs at about 15-20fps, while on a 486 it runs at 60fps and never slows down.  However Shadow of the Beast will not boot at all in 486 modes.

Over the years I've noticed that there are basically 2 categories of people that buy Towns machines.
1.  People that really want to explore the greater library, all of which own a 486 machine.
2.  People that only have a 386/Marty and usually only own 10 games or less (Splatterhouse, Tatsujin Oh, maybe Rayxanber, and some random hentai).

[kamiboy]

Bwaha ha ha, shadow of the beast. I wouldn't touch that garbage anyway, better install a 486 to ban it from my Town(s). "We don't like yer kind here, boyh!" My 486 cpu-sheriff will say as shadow of the beast tries to roll into town in his ugly ride.

And rest assured I won't be owning any games for my FM Towns, not at those absurd prices. I'll just be burning copies of the more standout titles, so I guess I am more in the category 2. While I do love exploring I find with my x68000 that since I am so picky exploring is all I'll ever do. The only games that interest me enough to warrant thorough play are the stellar ones, which are only a handful.

Although, there aren't exactly a lot of videos on youtube showcasing the libraries of obscure Japanese PC's, so who knows, there might be hidden gems.

Pretty much the only Towns videos on youtube are by you, Lukemorse1 and a few others. Maybe I'll do one once I get my system.

Anyway, say I get a Cyrix 486DLC 40mhz cpu, what sort of crystal would I need to drive that? I assume there is an exact hertz rating needed from the crystal, but which?

[famiac]

I'm curious too. The crystal is 32 Mhz, so it seems the frequency gets halved. I think the FM Towns II hardware maxes out at 20Mhz, so i would get a 40Mhz crystal.
Is this a correct deduction?

[kamiboy]

Well, my Towns arrived and is currently spread all over the floor.

To celebrate the occasion I thought I'd contribute to the small cadre of videos on youtube regarding FM Towns, and other Japanese PC's.

https://youtu.be/YgQcQUPkRNk

[SuperDeadite]

Welcome to the mediocrity.     In all seriousness, the Towns library has a lot of fun to be had, but be sure you go into it with the right mindset.  Internet info on the Towns is filled with misinformation and half truths.  None of the arcade ports are perfect, for every 1 thing I love about the system, there are 3 things that annoy the hell out of me.

Its the kind of system I would never recommend anyone buying, but I have no intention of ever selling mine either.    For pure gaming fun the X68K and the MSX shit all over the Towns imo.  But I actually own more games for the Towns then I do for the SuperFami lol.

[kamiboy]

Yeah, I already knew what I was getting in to. I would have gotten the MSX instead, but I honestly find them to be very ugly machines, whereas the FM Towns is quite sexy. My next piece of hardware is going to be an MSX though.

Also I do not care for the very underwhelming hardware that Microshit designed the MSX with. Really hampered game design until the later iterations of the hardware somewhat rectified that misstep.

I do not find the pre-8bit look and feel of most MSX games to be charming at all.

[kamiboy]

One thing I don't understand is that the crystal oscillator in the my Towns is rated 32 mhz, but the CPU runs at half that speed, 16mhz.

If I upgrade the cpu to a 40mhz one does that mean that I would need a 80 mhz crystal to drive it proper?

[famiac]

I would expect that the hardware on the towns has clock speed limitations. I've heard that most can't handle much above 20Mhz.

Try using a 40Mhz crystal first.

[kamiboy]

Ah, I never considered that driving a cpu with a crystal running at a speed lower than the cpu is rated might work.

I guess I can jus buy a DLC 32 mhz processor, which is much cheaper and get a 40mhz crystal to drive it.

One last question, what sort of socket solution would you use for the pins of the processors involved?

Any cheap ready socket solutions available on ebay? What did you guys use?

[RobIvy64]

OK, so I've actually performed this upgrade. Let me clear up some of the speculative posts from the armchair experts

I ended up using the Cyrix Cx486Drx2 after trying several of the other 386->486 upgrade CPUs. I tried every upgrade CPU available. The Cyrix Cx486Drx2 is not an easy chip to find, and the clock doubling and fast cache are only enabled via a Cyrix utility... which you can't run on the FM Towns. I have the Srx2 SX version in a laptop and the Cyrix utility really makes a difference.

I was only able to increase the CPU core clock speed to 18 MHz and keep the machine stable. This is a limitation of the system RAM being too slow. I suspect you could swap the onboard RAM (soldered), or get clever and program some type of wait states, but there is no point.

The speed increase it noticeable, but mostly negligible. Galaxy Force II actually switches to 60 fps mode when a 20 MHz or faster CPU is detected. I was able to get the machine to boot at 20 MHz a few times and GFII simply punished it. I found 18 MHz to be faster in that game.

Hope this helps Kamiboy, and good luck! Your results may vary since you have a slightly different model with a different motherboard, so I encourage you to give it a shot! It's still a fun experiment and I had fun trying it out

[kamiboy]

Why did you end up using such a rare iteration of the upgrade processors? Did the others not work at all, or were they just not fit for overclocking the Towns.

If the DRx2 is the only one that works then I am going to skip the CPU upgrade route. Getting hold of that processor on ebay for a reasonable sum won't be fun.

I may create a socket for my processor while I have the mainboard exposed, but only if I have the parts on hand, we'll see. For now I am albow deep in capacitor limbo.

[Opethian]

wb rob
I still got your upgraded downs

[RobIvy64]

Dibs on the downs if you get rid of it 

Kamiboy, all of the upgrade processors work fine with the exception of the Intel RapidCAD. The Drx2 was the fastest of all of them, with the Texas Instruments chip being a close second.

I had to find the CPU in ope's FM Downs on TaoBao.

[kamiboy]

Well, I guess I'll install a socket and keep an eye out for an upgrade cpu on ebay. Funny thing about really super obsolete electronics that should be worthless is that the people who put them up for sale on ebay know only maniacs would buy them, so they always demand a burger king's sum.

Would you happen to have any recommendations as to which socket solution I should buy for the cpu?

[RobIvy64]

I just took the CPU to my local electronics parts store and bought a machined PGA socket. I forget how many pins the 386 is, and way too lazy to look it up!

[kamiboy]

Yes, that is enough info to lead me the right way. Seems the 386 was a 132 pin cpu, but I'll have to verify. As expected the cpu sockets cost a tiny fortune. Seems every tiny thing I need for this project is going to set me back 15-20 each, which adds up quickly.

Not to mention all those capacitors I've got to buy are going to set me back a small fortune.

[RobIvy64]

Don't buy components off of ebay. Order from an electronics parts supplier like DigiKey or Mouser. You'll pay way too much off of ebay.

[kamiboy]

Unfortunately living in Europe means electronic components are most often cheapest bought from eBay. Shipping and duties kill most deals found outside of the European trade bastille. My best bet is always to order things from chinese sellers who offer free shipping and unbeatable prices that puts the item cost below duties threshold. Alas stuff from them takes a month to arrive, and often gets lost underway.

I think for the cpu I am just going to buy generic single row sockets and install as many as I need. They cost next to nothing shipped from Chinese sellers. For the CPU and other exotic components I'll just have to play the waiting game.

I may also look into getting some RAM, but it sounds like the Towns computers impose very rigid speed requirements on installed memory.

[kamiboy]

On second thought I am going to give up on that cpu upgrade idea.

Tried to take a soldering iron to the cpu pins today and it was immediately obvious that I do not have the proper equipment to desolder stubborn tiny pins of this type. Would need a heat gun, HAKKO or a some sort of chip quick.

If I keep at it with my current equipment I could prolly get the job done, but most likely with some damage to those tiny traces or solder pads. Let sleeping dogs lie I say, 16mhz 386 power will have to suffice.

[famiac]

I wish i had the same sense as you. Even with a hakko, i couldn't desolder the pins and ended up ruining my motherboard.

I can help you with finding RAM if you'd like

This is the cpu socket i bought, just for reference:
http://www.ebay.com/itm/121396874599?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[kamiboy]

Ouch, pains me to hear that, but I will take you up on that ram upgrade help. I was looking into it today actually. From what I've digged out it has to be 100ns SIMM 72 pin memory, I think 8mb max.

Though I am not sure whether it is even needed for the games or not. I think the 20F that I've got comes equipped with 2mb by default. Is there a memory requirement per game list out there?

I figure anything that could run on the Marty would not need more ram than I already have.

Rob, you mentioned in that video of yours that your friend desoldered your cpu inside of 10 minutes, what sort of equipment did he use?