Upgrading the Mega-PC?

A rather unusual peice of hardware but I opened her up to replace some RAM (un-successfully so stuck with 4MB at the moment) but I see some options for extra VGA Video Memory chip slots (the 2 solderd are labeled "AAA1M304P-07" giving a total of 256k on board) and a PLCC style Co-Processor slot. It got me thinking too, I have recently gotten into some DOS games and thought this could be a great machine to play them. Most of the stuff pre mid 90's works on it as a rule, but sometimes suffers slowdowns and it could do with just the slightest of boosts. I totally understand that it's VERY limited with what one can do but it would be nice ot have a more useable 386 PC since I plan on getting an old PII @333 machine someday.

I can't see the CPU (386SX @25mhz) but I doubt that anything can be done about it, I should think it's solderd onto the board.

Has anyone here got one of these that they have upgraded or know anything that can be done? :unsure:

Any help would be much appreciated.

P.s. Battery has been sorted with a coin type. :)

The 386sx can be upgraded. Either look for a CPU clip-on upgrade as those we are looking after for the Commodore bridgeboard (not easy to find) or desolder the CPU and solder inside a 486SLC CPU (pin to pin compatible with 386sx but has more cache and a 486 instructions set) and overclock a bit.
In case you need them, i have a suitable CPU 486SLC-25 made by Texas Instrument (Cyrix clone).

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Originally Posted by Xanxi

The 386sx can be upgraded. Either look for a CPU clip-on upgrade as those we are looking after for the Commodore bridgeboard (not easy to find) or desolder the CPU and solder inside a 486SLC CPU (pin to pin compatible with 386sx but has more cache and a 486 instructions set) and overclock a bit.
In case you need them, i have a suitable CPU 486SLC-25 made by Texas Instrument (Cyrix clone).

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Well I couldn't possibly think of de-soldering the thing, I think it's one very like this: http://upload.wikimedia.org/wikipedi..._AMD_386SX.jpg, except at 25mhz.

I do have a good friend of mine that has god-like soldering skills but I couldn't put that sort of work on him either, even if it was possible.

Howerver, these "clip-on" upgrades sound interesting, do they work like them old "Intel Overdrive" ones from the early 90's?

If i were you I would look for a complete swap mobo - mem- for a 486 DX4. That gives you compatibility and speed. The 386 will rule out some dos games.

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Originally Posted by jvdbossc

If i were you I would look for a complete swap mobo - mem- for a 486 DX4. That gives you compatibility and speed. The 386 will rule out some dos games.

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Not really an option since the Amstrad MegaPC is a unique motherboard and how it intergrates withthe Megadrive half of the machine. Plus the case is unique to that model.

I forgot to mention that I do have a 486DX @100mhz in my Acorn RiscPC, but I intend on using this 386 instead, since it runs even older games better. Often higher CPU's speed up the games a massive ammount thanks to the lack of programming effort where they only made games for a specific CPU using it's limits to cap the speed.

I had one of these that I found at a car boot sale around 10 years ago. (I also bought one new many years before but thats a sad story for another day) I tried to upgrade it too but found it was a small nightmare. Firstly the soundcard (adlib) is built onto the Megadrive board. I wanted to upgrade to a Soundblaster, but once you plug one in, it conflicts with the adlib side of the MD board. If you take out the Megadrive board the whole system fails to work so you are stuck with a pre Soundblaster soundsystem (which quite frankly sounds horrible).

I upgraded the 1MB ram (4 X 256K) to 4MB (4 X 1MB) but it wouldn't accept any more than that. I also upgraded the hard disk to 100MB from the standard 40MB. CPU wise its completely soldered on, and as you say, its a custom board that you can't swap out. Amstrad did make a 486 model at some point but i'd imagine finding a board would be hard, if you could though, it might be possible to swap out the 386 for the 486 type.

I ended up using the machine as a cool Megadrive (the GFX look awesome on the VGA monitor) And did attempt to make a Mega CD interface cable to connect to the front of the machine (connector near the cartridge port under a flap) but it didn't work. I ended up giving it away to my cousin who still has it somewhere.

But basically, your probably not going to upgrade it any more than it already is. It wasn't made for that really.

Hi Tokyo, can't tell you much about upgrading the machine but i can tell you it was me who swapped the coing type battery into it. The previous owner had replaced the original battery with another barrel type and i wasn't comfortable with it so did the same coin hack as on the amiga's with the diode, wasn't sure if this was required but added it to be on the safe side.

As far as i remeber it only had 1mb memory when i sent it to you or was i mistaken and it had 4mb already?

I did however manager to install a larger hdd in there, i had a 500mb running at one point but took me forever to work out how to get in the bios to get it to boot the dos floppies to install the software. If i remember correctly to access the bios its something like ctrl+S and to boot the floppies you have to set the boot mode to full instead of quick or it skips the floppy at bootup and tells you no system disk or something along those lines.

Was a while ago

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Originally Posted by Phipscube

I had one of these that I found at a car boot sale around 10 years ago. (I also bought one new many years before but thats a sad story for another day) I tried to upgrade it too but found it was a small nightmare. Firstly the soundcard (adlib) is built onto the Megadrive board. I wanted to upgrade to a Soundblaster, but once you plug one in, it conflicts with the adlib side of the MD board. If you take out the Megadrive board the whole system fails to work so you are stuck with a pre Soundblaster soundsystem (which quite frankly sounds horrible).

I upgraded the 1MB ram (4 X 256K) to 4MB (4 X 1MB) but it wouldn't accept any more than that. I also upgraded the hard disk to 100MB from the standard 40MB. CPU wise its completely soldered on, and as you say, its a custom board that you can't swap out. Amstrad did make a 486 model at some point but i'd imagine finding a board would be hard, if you could though, it might be possible to swap out the 386 for the 486 type.

I ended up using the machine as a cool Megadrive (the GFX look awesome on the VGA monitor) And did attempt to make a Mega CD interface cable to connect to the front of the machine (connector near the cartridge port under a flap) but it didn't work. I ended up giving it away to my cousin who still has it somewhere.

But basically, your probably not going to upgrade it any more than it already is. It wasn't made for that really.

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Well I got no intention of changing the sound card at all, to be honest, the games designed for the 386 mostly only had Ad-Lib support anyway so that's not an issue. However, there are a few aspects that could be upgraded quite easily. VGA RAM for a kickoff, like I said before it takes these small rectangular chips labeled as "AAA1M304P-07". I've done a bit of Googling and there are chips pretty much the same as that and apparently other Mega-PC units used variants of that Video RAM chip.

Also Google revealed that it can take hard drives at a touch over 500Mb (but no more) plus it should take 16mb of RAM but I tried some 4mb SIMM's and it doesn't like any of them. Theres spaces for a further 4 sockets so maybe it doesn't accept SIMM's larger then 2mb? If that is the case then one would need to solder them extra sockets on but I'm unsure if it requires more then just adding extra sockets or if it's a much more complicated affair.

One thing I would REALLY like is to make use of the empty PLCC Co-Processor plug. I would think it's for a 25mhz i387SX FPU, I might put a wanted ad for one sometime in the future... (Check attachment).

A 486 model would be rather swish but the chances of coming across with one of them is the same likelyhood of finding the illusive rocking horse waste.

Still, I'm actually talking to a good friend of mine to arrange a mini project if we can get it to communicate with a Mega-CD, it won't be pretty but there's no reason why it wouldn't work. :)

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Originally Posted by scrappysphinx

Hi Tokyo, can't tell you much about upgrading the machine but i can tell you it was me who swapped the coing type battery into it. The previous owner had replaced the original battery with another barrel type and i wasn't comfortable with it so did the same coin hack as on the amiga's with the diode, wasn't sure if this was required but added it to be on the safe side.

As far as i remeber it only had 1mb memory when i sent it to you or was i mistaken and it had 4mb already?

I did however manager to install a larger hdd in there, i had a 500mb running at one point but took me forever to work out how to get in the bios to get it to boot the dos floppies to install the software. If i remember correctly to access the bios its something like ctrl+S and to boot the floppies you have to set the boot mode to full instead of quick or it skips the floppy at bootup and tells you no system disk or something along those lines.

Was a while ago

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I remember you saying about the battery, that's a real neat mod you did there. :thumbsup: Also thanks for the info about the BIOS, that would be very handy since I plan on fitting a larger hard drive. :)

Hey,

I've recently bought a MegaPC and I was interested in upgrading a couple of bits and pieces. Do you have any useful information for me?

I was on the hunt for an 80387SX ALU, not much luck without spending a fortune!

What RAM did you use?

Can you recommend any VRAM to use (DRAM 256k)?

Your best bet for finding an 80387 on the cheap is probably to go to your local recycle center and see if they have some old PCs lying around - if you can find some 386 boxes to root through, one of them might have a 387.