FS-A1WX memory upgrade and minor repair info

By wyrdwad

Paladin (836)

Аватар пользователя wyrdwad

15-02-2020, 18:27

Hey guys,

Total hardware newb here (I've never touched a soldering iron in my life!), but I figure enough is enough, so I want to get this beautiful system of mine upgraded and fixed up, one way or another!

My big question is about upgrading the RAM in it, as I'm still on the base 64 KB that came standard from the factory -- I've been looking for info online about it, and I found some VERY old topics on here that seem to suggest the specific RAM chips I'll need have the model number 414256, and I'll specifically need four of them. Is this correct? And if so, do they have to SPECIFICALLY be 414256 chips? A cursory search for these chips online brought up 514256 chips that claim to be 414256-compatible, and I found some very similar-LOOKING chips when I went into Akihabara the other day, but they were model number 41C256. Would these work, or should I ONLY use 414256es?

Also, can anyone suggest anywhere to buy these chips online, that will deliver to Japan? Or even better, any stores in Akihabara or elsewhere in the greater Tokyo area that sell them?

ALSO also, once I get the chips, is there any sort of guide online that shows EXACTLY what needs to be done to install them? Preferably with pictures/diagrams or the like? I saw that you have to be super-careful with them, and flip a few jumpers, both of which have me super scared (I'm terrified of damaging my baby!).

I have a friend who lives nearby, and he actually DOES own a soldering iron and has VERY LIMITED experience soldering chips into Game Boys and the like -- and he said he'd help me out. But he's never worked on anything like an MSX2+ before, so the more specific and finely detailed information I can get, the better.

And on that note, the other thing I want to do while my MSX is opened up is get my controller port 1 repaired -- specifically, it sounds like the solder on the board needs to be re-flowed, and possibly have some flux added to it? Meits wrote up a super helpful guide on how to do this here:

https://www.msx.org/forum/msx-talk/hardware/controller-slot-...

But again, the person I'll be getting help from has limited soldering experience, and has never soldered anything like an MSX before, so if there's anything anyone can add to Meits' instructions that might be helpful for a total amateur to know (such as... what kind of flux to use, maybe? If that's even a thing?), I'd be SUPER-DUPER appreciative for the info.

Thanks very much, and sorry to ask stupid questions!

-Tom

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By Wild_Penguin

Hero (598)

Аватар пользователя Wild_Penguin

15-02-2020, 19:37

Hi wyrdwad (or Tom),

You are in luck in the sense this computer has a lot of documentation linked in the Wiki.

I'm not sure where you got the idea of using a 414256 chip - those seem to be a DRAM chip? This computer is using a 8464 chip for the RAM (two of them); seems like they are 4bitx64k SRAM chips. Do not put DRAM chips into a computer which used SRAM chips in the first place!

EDIT: Scratch the above, I misred the schematic. But the fact is, many similar / identical chips (from different manufacturers) have slightly different part numbers. Compare their datasheets and pinouts - if they match (and the chip tells it is a DRAM chip of Abit X BBk) - then it will work!

I could be in the wrong, however.
I would go about this problem with the following steps: 1) look at the links in the Wiki with Google Translate 2) get someone even more experienced with soldering and memory mappers. Repairing / reflowing the joystick port might be trivial, but de- and resoldering stuff on the MB is not - especially if you are not 100% sure what you are doing (and: there is only one MB!)! 3) get the documentation and plan 100% ready (i.e. it should work on paper!) before attempting the upgrade.

I'm certain there are other people who will help you with part 3) on this forum!

By Meits

Scribe (5899)

Аватар пользователя Meits

15-02-2020, 19:48

This is a video you want to watch (and google translate). To me it mostly looks quite doable, but I can imagine that fiddling with the engine might be a bit scary.

By wyrdwad

Paladin (836)

Аватар пользователя wyrdwad

16-02-2020, 12:18

Thanks for the comments, and for the video link! That video seems like it'll be SUPER helpful.

Is there any easy way to tell if the RAM chips I find out in the wild will be usable in my MSX? I can't stress enough how wildly unprepared I am for this, but I swear that 41C256 chip I found in Akihabara seemed like the right thing. What can I do to ensure it is? What can I look for before I buy it?

Also, for re-flowing the controller port, it was suggested I add flux. How much should I add? And is there any special type of flux, or is all flux pretty much the same?

Thanks again!

-Tom

By Meits

Scribe (5899)

Аватар пользователя Meits

16-02-2020, 12:21

As for the reflowing. Reflowing is easy. Just hold your iron against the join until it melts and then let go.
Do keep in mind that this is the least desired option. You'd better remove the old solder and put some new solder on it. The kind of flux is not too important. I did mine without and it worked just fine.

By Wild_Penguin

Hero (598)

Аватар пользователя Wild_Penguin

16-02-2020, 13:18

Most solders have flux in them (as a hobbyist: don't use solder which does not have flux in it). Flux might be useful when removing the old one, but you should not need additional flux when soldering trough-hole components. Soldering SMDs can be a different thing.

EDIT: There are some good soldering tips in the instructions for this very RAM upgrade...

By Wild_Penguin

Hero (598)

Аватар пользователя Wild_Penguin

16-02-2020, 13:15

As for the memory upgrade:

Good thing you are asking here for help!

First, the 41C256 is the wrong kind. If you look at the schematics (linked in Wiki) you will notice the chips are 20pin chips. Moreover, in the schematic there are two chips with 4 data bits -> this tells that the chips must be 4 bit x 256k. 41C256 is a 256k x 1bit chip - so it can not possibly work for this upgrade!

Also, there is an English RAM upgrade instructions linked in the Wiki. In that instruction, they are called 44256 chips (as opposed to the schematic where they are 81C4256 chips). This nomenclature difference is especially what I was referring to - the names might be slightly different, but what needs to be done to determine if a chip is compatible, is to check their datasheets (with pinout) and their long name - i.e. the Xbit YYYK DRAM -part. If you look by Google for 44256 datasheet or 81C4256 datasheet you will notice they are identical for practical purposes (as are some other, differently named chips). (EDIT: Noticed they have listed the most - if not all - compatible chips later in the instructions)

To summarize: get the datasheet for 44256. Compare that to the datasheet of whatever you are buing. You should be buying 256k x 4bit DRAM memory chips, 20-DIL (or DIP) package.

The most dangerous part here is de-soldering the old chips. Please get someone experienced enough to do that! Damading the MB can not be undone (and you are dealing with data and I/O lines here; if one is shorted or broken, that will be the end of the MSX unit...).

By wyrdwad

Paladin (836)

Аватар пользователя wyrdwad

16-02-2020, 14:03

Yeah, I think for the time being, I'm just going to fix the controller port. I'm starting a new job in Tokyo this April, and will have better access to skilled solderers then (I hope!), so I'll wait until then to try something like this.

...Or, maybe I'll just save up and buy that tR I've been wanting! That could work too. Wink

-Tom

By jltursan

Prophet (2289)

Аватар пользователя jltursan

16-02-2020, 19:56

Forget about the 512KB upgrade, you'll need someone really expert as you'll need to mess with the MSX engine and there're tiny legs out there. 256KB are enough for a gaming machine and it's much more easier mod. You'll need only 2x44256 or equivalent ICs, probably speed wouldn't be a problem, all of the ICs of these generation are faster enough.

And if you think that there's some risk to damage the motherboard unsoldering old chips; don't doubt, cut the legs and then, desoldering the legs will be an easy task.

One think I can't remember if there's enough space to fit some sockets without touching the keyboard...

By sd_snatcher

Prophet (3296)

Аватар пользователя sd_snatcher

17-02-2020, 15:41

Yes there is space for sockets, and IMHO they're mandatory for any old PCB maintenance.

But all MSX2+ PCBs have non-metalized holes, because to lower costs they were build with the same machinery used to build TVs/VCRs/stereos.

The tip is that this means you have to be extra careful to make sure that the sockets are well seated in the PCB. Otherwise, the pressure you make to insert the chip in the socket will be applied directly to the tracks of the other side and will rip them off the PCB.

The procedure to make sure that they socket are well seated is simple, but must be followed. In fact, it's recommended to use this procedure on any PCB. And, curiously, this procedure seems to have become a forgotten ancient knowledge, since technicians are not used to work with single sided PCBs anymore.

1) Place a single socket into place
2) Solder only the pin-1 and the farthest diagonally opposed pin, to fix the socket into place
3) Now hold the PCB vertically, apply pressure over one of the soldered pins and heat its solder spot again. You should hear a "tec" sound as the socket seats into place
4) Repeat the step (3) for the diagonally opposed pin
5) Now solder the opposite pair of diagonally opposed pins, repeating the steps 3 to 4
6) Now find the two centermost pins that are also diagonally opposed. Repeat the steps 3 to 5 for these four pins
7) Now you can solder the rest of the pins are usual

Bonus tip1: This kind of PCB is one of the few cases where I would also recommend the use of stamped IC sockets (square holes) instead of machine tooled IC sockets (round holes), because the stamped ones are more flexible and transfer less pressure to the PCB tracks.

Bonus tip2: Since you're not experienced with soldering, DO NOT try to salvage the old DRAM chips. Buy a high quality cutting plier and cut all the DRAM pins to remove the chip. Then place the PCB vertically, apply the soldering iron to the solder, and pull the pins out of the PCB from the other with a normal plier. Repeat this for each pin individually until all pins are removed.

Bonus tip3: This PCB has a pair of jumpers (J2/J3) to select the DRAM size. It will be better if you install a real jumper in that place like I did on my machine. It allows you to easily select the DRAM size, for testing. Remember that you have to cut the J2 open on the lower side of the PCB.

Bonus tip4: the longer pin of the J2/J3 jumper set was taken from a dual-row right-angle pin header.