Zalog wrote on 2020-07-14, 09:31:

It looks like there was planned space for another 16bit ISA slot on the reverse of the riser (locations are marked J5/J6) - and probably left out to save costs and a backplate re-design too.
I am wondering though if this feasible to add an 8bit slot to J6 so that a small internal ISA card (maybe an XTIDE) could be added... as there does look to be just enough room for a small card in there 😀

Yep! It was one of the first things I noticed 🤣
If you solder there a 8bit slot it will work - it will barely fit as the drive cage is in the way. Some small XT-IDE or some small card to add a boot rom should fit .
I even bought some 8bit isa slots from mouser last year but I abandoned the idea since that special card's idea was conceived.
The lack of expandability really hurt the system....

If you solder there a 8bit slot it will work - it will barely fit as the drive cage is in the way.

Lack of expandability really hurt the system....

Yes, it does look very tight in there - probably too tight to do anything really useful 😔. I think your decision is the better option - will have to wait for a special card to fix multiple problems in one go! BTW any chance it'll come with two line-ins (?) I'm thinking of adding a Backpack CD-drive - but realised that CD audio is going to require a bit of audio jack swapping if I want to use it as the megadrive is currently occupying the existing line-in port on the current awe card!

Totally agree with that, only one free slot limits things massively - if they had added a bit more expandability it would have made our lives a lot easier - but less interesting 😉😁

how will you connect the external cdrom?
backplate of card is pretty much full atm though...

keropi wrote on 2020-07-14, 21:07:

how will you connect the external cdrom?
backplate of card is pretty much full atm though...

I've decided to go with a Backpack CD drive that connects through the LPT port. I had thought of attaching to the IDE, but it requires cutting and when I thought about it the LPT option would be easier and meet my needs, so there isn't much point doing any modification. The drive will only do 2x speeds as the Amstrad's LPT port is only Bi-directional and will eat a little RAM when it's plugged in, but that will be good enough to install games and run CD voices/audio on "talkie" adventure games of the time which is all I want it for. I've got a later model which is a CD-RW (I'll never use the RW function in DOS !), but wish I had the earlier version as the case style matches the Mega-PC so much better - still as I'm not going for a fully anthentic look, I think I can live with it for now 😁

Yes, thought that might be the case, the card is packing huge functionality into a single slot, frankly I'm amazed you've got as much in as you have - it'll be an amazing piece of kit 😎 I think I may have a solution to the cd-audio problem though, so don't worry about adding an extra one - I've remembered I have an old Yamaha speaker stored in the loft somewhere which has two line-in ports. That would allow me to connect the CD-drive to one port and the Mega-PC to the other and do the mixing on the speakers - that's probably a simpler solution to the problem, so will have a dig around some time and get them out when I get a chance........

Zalog wrote on 2020-07-15, 08:42:

I've decided to go with a Backpack CD drive that connects through the LPT port. [...]

Ah , a LPT cdrom... how does it perform? does it bring the cpu down on operation?
A seconday line input can be possible but it must be further down the pcb
This might not be an issue though since the megapc card will NOT have a full bracket. The reason is because there is NO air intake on the system shell!
It might not be an issue with a 386sx board but a 486slc benefits from fresh air intake. It is quite a fail of amstrad , the psu fan just does not have fresh air to circulate outside the case.
Bracket will be something like this, just enough to secure the card in place:

There is also 1 easy solder joint required for the scandoubler function . This cannot be avoided since we need the pixel clock signal on the md side to reach the scandoubler fpga.

keropi wrote on 2020-07-15, 15:46:

Ah , a LPT cdrom... how does it perform? does it bring the cpu down on operation? A seconday line input can be possible but it m […]
Show full quote

Zalog wrote on 2020-07-15, 08:42:

I've decided to go with a Backpack CD drive that connects through the LPT port. [...]

Ah , a LPT cdrom... how does it perform? does it bring the cpu down on operation?
A seconday line input can be possible but it must be further down the pcb
This might not be an issue though since the megapc card will NOT have a full bracket. The reason is because there is NO air intake on the system shell!
It might not be an issue with a 386sx board but a 486slc benefits from fresh air intake. It is quite a fail of amstrad , the psu fan just does not have fresh air to circulate outside the case.
Bracket will be something like this, just enough to secure the card in place:

There is also 1 easy solder joint required for the scandoubler function . This cannot be avoided since we need the pixel clock signal on the md side to reach the scandoubler fpga.

Yes seemed like the best plan - with the Amstrad LPT port I'm getting data rates of slightly above 300KB/s which is 2x CD-ROM speed - not exactly blisteringly fast but good enough. The drive does have an impact on the CPU when its in use, but I haven't fully measured it yet. When it's not doing anything or playing CD audio then there isn't a noticable impact, but when transferring data there is an impact. Just from the feel of things from what I've tried so far the machine performs more like it has a 25Mhz processor than the 33Mhz it has in - but for games such as 'Sam and Max' or the original version of 'Warcraft' its fine.

If a secondary line could be added without too much trouble, that would be wonderful - it would give folk a way to add in a CD music (or other source) input into the mix which would be fab. Totally agree with you not adding a full bracket (love the securing bracket idea 😀 )- the airflow inside the case is minimal and in many places non-existant (!), so a decent intake would be a very good idea and would help the 486slc.

That sounds fine, there isn't any other way to get that signal really - will the connection be made with a wire soldered to the mega board that has a connector on the other end, so that it would slot over a jumper pin on the new board and thus make removing the board easier (?) - not that you'd be doing that often given everything that it'll have on it ! 😁

Zalog wrote on 2020-07-16, 07:15:

Yes seemed like the best plan - with the Amstrad LPT port I'm getting data rates of slightly above 300KB/s which is 2x CD-ROM speed - not exactly blisteringly fast but good enough.
[...]

Interesting, perhaps the only real solution to add a cd-rom to the system... I will look for one as well 🤣
the scandoubler signal will probably just be a 2pin header: clock+shielding so it will be removable
line-in #2 stays 😉

also:

This is a dream machine. Really. When I had my 386 and a Megadrive I really wanted to get one..

keropi wrote on 2020-07-16, 14:38:

line-in #2 stays ;) […]
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line-in #2 stays 😉

also:

That's fab news, thanks for keeping the extra line in. The scan doubler connection sounds also sounds a very sensible solution - can't wait to see it in action 😀

Oooooooooh!!! Looks like your cirrus logic 5428 has arrived - guess we'll be seeing the ultimate version of the megapc on vogons soon - good luck with the transplant 🍀👍

allright - did the transplant and it was a success !
- SpeedSYS reported a bump in video memory from 3.085kb/sec to 7.850kb/sec
- Wolfenstein3D benchmark gained 2fps , doom some ~1.5fps - these are cpu-bound so no surprise
- win3.11 reported a massive boost in performance - as expected since 5420 had 0 acceleration features whereas 5428 has plenty

Here is a comparison under win3.11 - Winbench93 and WinG performance tool used:

Full 1mb reported and used - you can now select non-interlaced 1024x768 resolution under win3x as well provided you run CLMODE before to configure the chip with the proper monitor selection.
1280x1024 is always interlaced so it's a CRT-only resolution.

bonus pics from the process:

Since I have 16MB installed on the system UNIVBE disabled the LFB modes - not sure they make any difference in non-vbe2.0 aware applications.
I also had to write a different BIOS for the system - so a proper CL5428 one could be used. I will attach it here just in case anyone else needs it.
Tried 4-5 of them and this generic 1.4 one behaved the best.

So this is the final result, heatsink added to 5428 and a label resembling the original one fitted on the new bios chip 😁

So does it worth it? If one plans to stick to DOS 2D games maybe not, there is no speed change to justify it. But if someone can do the transplant why not? GUI acceleration is significant and bragging rights big 🤣

keropi wrote on 2020-07-17, 14:26:

allright - did the transplant and it was a success ! - SpeedSYS reported a bump in video memory from 3.085kb/sec to 7.850kb/sec […]
Show full quote

allright - did the transplant and it was a success !
- SpeedSYS reported a bump in video memory from 3.085kb/sec to 7.850kb/sec
- Wolfenstein3D benchmark gained 2fps , doom some ~1.5fps - these are cpu-bound so no surprise
- win3.11 reported a massive boost in performance - as expected since 5420 had 0 acceleration features whereas 5428 has plenty

So this is the final result, heatsink added to 5428 and a label resembling the original one fitted on the new bios chip 😁

So does it worth it? If one plans to stick to DOS 2D games maybe not, there is no speed change to justify it. But if someone can do the transplant why not? GUI acceleration is significant and bragging rights big 🤣

Well done 👏 that's fantastic work ! Getting the 5428 installed is a bit step forward and is a nice improvement - you definitely deserve bragging rights !!!
As the 5428 gives a little extra performance and allows access to the full 1MB (well above 256kb in my case😉) then it could be a benefitial mod for some later DOS games - I'll just have to look around for someone in the UK with the same amazing skills to help me (i'm way to clumsy for such delicate work) 😞
Actually the acceleration for windows is an important improvement, since it may mean that games such as the first version of Myst should ok on win3.1 - that in itself would be a big achievement 👍
The bios sticker is a nice touch - it looks so original you can't tell its a new chip !!
Can't wait to see your MegaPC when it's had everything done 😄 - thanks for all the inspiration !

Zalog wrote on 2020-07-18, 15:27:

Actually the acceleration for windows is an important improvement, since it may mean that games such as the first version of Myst should ok on win3.1 - that in itself would be a big achievement 👍
The bios sticker is a nice touch - it looks so original you can't tell its a new chip !!
Can't wait to see your MegaPC when it's had everything done 😄 - thanks for all the inspiration !

Myst? You might be lucky then. 😁 It uses QuickTime VR and QuickTime 2.x (16Bit) has direct frame buffer support for certain VGA chips built-in, too!
Just check the help dialog in QuickTime's Control Panel applet.

Jo22 wrote on 2020-07-18, 20:30:

Myst? You might be lucky then. 😁 It uses QuickTime VR and QuickTime 2.x (16Bit) has direct frame buffer support for certain VGA chips built-in, too!
Just check the help dialog in QuickTime's Control Panel applet.

😁That's fab news, myst is one of my favourite games and being able to play it on the MegaPC would be awsome !
I never knew Quicktime had support for Cirrus Logic (shows how much I looked in the settings 😉) - that makes it important to get the graphics chip changed on my machine, especially as......

I found my big box copy when searching in the loft for my Yamaha speakers 😂😂😂

If anyone has any ideas about where I can get the graphics chip change done in the UK, please pm me as I've not come up with any great results from a web trawl so far........🤔

You're welcome! ^^

I wish you the very best for the upgrade.
A chip capable of acceleration/colour conversion/scaling would be quite nice on Windows.

However, in case it's not possible..
QuickTime 2.x can also use DCI if the driver supports it. 🙂
Display Control Interface was essentially Windows 3.1x-only (Win95 was planned to have DCI32, but it never really materalized).
Some movie players like Xing MPEG Player also use DCI. .

Jo22 wrote on 2020-07-20, 21:34:

However, in case it's not possible.. QuickTime 2.x can also use DCI if the driver supports it. 🙂 Display Control Interface was e […]
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However, in case it's not possible..
QuickTime 2.x can also use DCI if the driver supports it. 🙂
Display Control Interface was essentially Windows 3.1x-only (Win95 was planned to have DCI32, but it never really materalized).
Some movie players like Xing MPEG Player also use DCI. .

That's good to know - may give it a go with DCI when I get chance to see how it performs 'as is' whilst I wait to find somewhere to do the upgrade.

Haven't had much time to do much on the MegaPC, but my Roland MT-32 (old) has finally arrived and has checked out ok🙂
Once I've got round to plugging it into the AWE card, it should give a nice additional option for music in Adventure games !

This is a bit off-topic, but I just read the news that Myst was "ported" to Apple II and thought you might find it interesting also.
- That page is no hacker site really, but a tinkerer's site. They often cover electronics, geeky art and such:
https://hackaday.com/2020/07/30/myst-demake-f … r-the-apple-ii/

This thread is awesome! I found it when doing a search on upgrading the Mega PC with a 486slc..

I bought a Mega PC back in 1993 when the price was cut to £599. I'd lusted after one for some time but the £999 price was too high.

I was shocked to find that it couldn't run some games any better than my Amiga CDTV. The machine was ridiculously crippled (for a PC), but I never realised back then when I bought it... I thought I was getting a rather powerful 25MHz machine with the ability to display 256 colours.. much higher than my Amiga..

I upgraded its RAM to 4MB and VRAM to 512KB and also put a Soundblaster pro in to get effects in PC games.. this caused issues with the MD card so I had to disable it when using SB.

I eventually had a machine that I very much enjoyed playing games on... Wing Commander, Monkey Island 2 (without all the disk swapping!) And Wolfenstein 3D to name a few. I also played Sonic to death on the Megadrive side.

Only about 6 months after, though, I felt stuck with the machine and wanted to do more... the advice from my local Amstrad dealer was to upgrade to 486... back then that meant getting a new machine at a very high cost (I never knew about the clip on upgrades)... I was a bit miffed and decided to sell it all and get an Amiga 1200... I still have that machine to this day and love it (I've made some rather crazy mods to it that I posted on Amibay some years ago).

The thing is, I really liked the idea of the Mega PC. I found out about the teradive in Japan which looked really awsome in black (reminded me of my CDTV) and for a while hoped that a more powerful version would appear... It never did..

Roll on 5 years later, 1998/9 i'm at a car boot sale and guess what I see?... A Mega PC all complete with monitor etc all looking in almost new condition for.... £5

I casually bought it, my face looking cool... but inside I was like.. OMFG!! Gotta run away with this fast before the guy realises!.. it was heavy.. so I walked very fast instead 😁

By this time, I had collected quite a few machines, one being a Mega CD which I thought would be fun to try on the Mega PC, but I couldn't find a cable for it... another Idea was to try to upgrade the PC. I had heared of the Mega PC plus with a 486 and figured out the board was also used in the Amstrad PC7486SLC. I managed to find one that I was given for free!

I got to a point where I had the board out of the 7486 and had ideas to making a cable to the Mega CD.. but never finished as I met a Danish girl and moved to Denmark.. that and alot of other projects got put on ice all left in my Mums loft in UK...

Soon after my son was born around 2006 I decided to sell off alot of my collection (pressure from Mum too), some really nice stuff (mint boxed Wondermega and Mega Jet to name a few... aaaarghhh!). I couldn't get rid of my Amigas, they were my main passion... and the Mega PC had captured my cousins attention who was 13 at the time and just recently discovered all things retro... I gave him it along with a boxed ZX81, Atari 1040STE and some other stuff... I said if he ever didn't want them anymore to give them back, don't sell them! I don't remember what happened to the 486SLC board...

I had pretty much forgotten about them...

Last month my aunt sends me a photo saying "look what we have found in our loft". Amongst it all is the Mega PC.. the monitor has gone sadly, but the PC, controllers, keyboard etc looks in really nice condition apart from slight yellowing. I've asked her to look around for the monitor... and a 'circuit board in a black plastic bag' (the 7486slc board in antistatic).

I also need to get someone technical to open it and take out the battery!

I plan to go over to UK in October all being well and pick it up..

So doing a little searching online I have now found out there seems to be a little following of folks for this fascinsting machine 😀

After reading this thread i'm curious about some things...

How to do the audio quality improvement mod?

If my 7486slc board can't be found, i'd like to try to upgrade the original 386sx board processor, GFX etc.. so..

Are there any differences between the original 386sx board and 486slc apart from the additional circuitry for the 486?

Does it seem possible to add the circuirty for Flush, A20M, KEN, BIOS L1 etc to the original 386 board?

Does the 386 board have the same 5420 GFX chip?

If so, could the 5429 GFX chip be added instead of the 5428? It seems like an even more enhanced GFX chip with support for higher memory clock and memory mapped I/O...

I have seen a ti486sxlc2 66mhz CPU was once made.. I can't find any for sale, but have come across the 50Mhz G version on ebay. It seems its a 3.3v powered part with 5v I/O tolerance... some have reported it works Ok in 386sx machines at 5V power so i'm thinking of giving it a try.. have any of you guys had experience with it?

Hi Keropi, its me phipsy from Amibay 😀 What is this "special card" you are making ? Seems like a soundcard and scan doubler of some kind... care to share more details?

hey phipscube !!! welcome aboard!
nice story - thanks for sharing! indeed the system has a cult following and true it was very weak , not only due to 386/486slc but also because it only has 1 free ISA slot...

The 386sx and 486slc mobo are completely different ones. Different chipset , different vga chips. The 386sx uses the WD90C00 vga controller - I have no idea if the later WD90C3x are compatible or not.
The 5429 I am almost certain it will work on the 486slc mobo but do not expect any wonders. It might offer better GUI acceleration but the bottleneck is the 486slc cpu , you can only go so far with it...
I would also not bother with upgrading the 386sx mobo with a 486slc or clip-on upgrade: the gains would be too low and the only thing that would make a difference - L2 cache - cannot be just added ... this is where the 486slc gains most of it's speed: the 64kb L2 cache.
About the audio improvement mod, these are the things I did on my board with Tiido's guidance since he is ultra knowledgeable about megadrives:

and this is the 60hz mod in case anyone needs it:

about that special card, it is a single isa card that combines lots of features missing in megapcs to make them more usable:
- soundblaster core
- opl3
- CMS support (switch between OPL3 or amstrad-opl2+CMS)
- 10mbps nic
- bootrom support (for xt-ide bios)
- covox dac support
- onboard wavetable synth based on SAM9733 + GS rom (basically an embedded TB Cancun/Dreamblaster Yucatan)
- expansion to add an optional PCMIDI daughterboard
- onboard scandoubler so one can use a VGA monitor for both PC and megadrive modes
- mixing of megadrive sound output via a fly cable at the back

I think that's all 🤣
basically you add one card and you get lots of functionality in return

phipscube wrote on 2020-08-10, 15:48:

This thread is awesome! I found it when doing a search on upgrading the Mega PC with a 486slc.. […]
Show full quote

This thread is awesome! I found it when doing a search on upgrading the Mega PC with a 486slc..

I also need to get someone technical to open it and take out the battery!
If my 7486slc board can't be found, i'd like to try to upgrade the original 386sx board processor, GFX etc.. so..
Are there any differences between the original 386sx board and 486slc apart from the additional circuitry for the 486?
Does it seem possible to add the circuirty for Flush, A20M, KEN, BIOS L1 etc to the original 386 board?
I have seen a ti486sxlc2 66mhz CPU was once made.. I can't find any for sale, but have come across the 50Mhz G version on ebay. It seems its a 3.3v powered part with 5v I/O tolerance... some have reported it works Ok in 386sx machines at 5V power so i'm thinking of giving it a try.. have any of you guys had experience with it?

Hi phipscube, thanks for the compliment on the thread, it has been a bit of a journey of discovery - the MegaPC does seem to be developing a bit of a cult following, probably as its the last real oddball PC that Amstrad made !

On the battery side - if the 386 one hasn't leaked then do cut it out asap - that said almost all of the boards I've seen up till now have had leaking batteries..... However the 486SLC is a better beast with a Dallas Clock chip and battery, so I'd definitely recommend pulling the old chip and replacing it with an Alt12887 (see pic) or similar since it allows you to remove and install the battery easily for storage - and a neater solution to modifying the Dallas.

On the 486/386 Keropi has answered re: the 386 MegaPC and the 7486 board (basically completely different boards) - however I can now confirm I've seen two genuine Amstrad MegaPC Plus boards recently, one working (held by a collector)/one not working with leak damage - these have the Ti486SLC 33MHz MAB chip soldered on in place of the 386 chip on the 7386SX board and have the 386SX 's 50Mhz clock crystal replaced by a 66Mhz one - the only other thing I can see is different is the BIOS which is part number 41652 and a Quadtel 486SLC (001034) chip which only enables L1 cache in a similar manner to the Cyrix upgrade CPU program does. I've looked into the prevelance of part numbers and an extract of what I've found so far is attached on this spreadsheet image.

The upshot of it is that (and in answer to your question), it probably isn't easy to add circuits for Flush, A20M, KEN etc to the original 386 board, but you could install the 486SLC 33Mhz MAB cpu on the 7386, change the clock chip and try and enable the cache etc.. using the Cyrix upgrade cpu enabling program which can be found on the web - but there could be stability issues and the performace gains won't be much (and less than the 7486 board). If you can find the 7486 board then go with it, as it is so much better, having MCA bus for graphics, more graphics ram, better CPU and cache (L1 and L2) that give much more performance. Realistically modifying the 7386 board wouldn't really be worth the effort, and it's fine for basic adventure games if your into them.

In answer to the ti486sxlc2 66mhz CPU question - this is again something I've looked into - since the chip is 3.3v powered, you would need to supply that seperately to the chip - from what I've seen supplying 5v directly to the chip doesn't tend to end well unless you get very lucky and get one of a very small early batch of chips. It's probably better and safer to supply 3.3v seperately and directly to the chip, and I've seen an Amiga Goldengate board modified to provide this - but it does require bending the voltage pins away from the board and a bit of work to provide a seperate 3.3v supply - not easy and definitely not for the faint of heart, but a quick google should find the page on Amibay.
From my research, there is an easier way to get a speed boost with no voltage modification or major board modification. This would be to solder a Cyrix 486SRX2 50Mhz "clip on" upgrade chip directly in place of the Ti486SLC 33Mhz (which has been removed from the 7486 board first !) - as these CPU's run off a 5v supply - but you would need to change the clock chip to a 50Mhz one to drop the board speed to 25Mhz to accomodate.

That said so far I've found the 33Mhz to be adequate for most of the stuff that I want it to do, and with the development of FastDOOM (see thread on this forum) - the 486SLC can run doom quite well through this route, so once the graphics chip has been upgraded then I think I'll be happy with it.

Will have a bit more to report at the end of the week as I've found a local PCB maintence firm who's going to do the graphics chip replacement for me - and I have a few upgrades in progress at the moment - until then I'll tantalise you all with the image of the NOS 5428 chip I managed to find for the upgrade !!

Hey Keropi, nice to be aboard, looks really cool here!

Ah yeah, ok it sounds pretty much impossible to make the original 386sx board run like the 7486... I hoped it was similar, never mind.. I will look into the GFX and see if its possible to put one of the newer WD paradise chips in.. I had a quick look at some data sheets and I don't think they are pin compatible....

I understand lack of L2 cache would be a crippler, but would having the L1 cache activated at least provide some increase? I think I saw 1kb on the cyrix chip and 8kb on the Ti...

Could you post a pic of your 386sx board just to have a look at please?

Thanks for the Audio and 60Hz mod! they look quite doable so thats nice. I contacted Tiido on Amibay and already bought 4x 4MB SIMMs from him 😀 that will go nice in any of the boards!

The special card sounds awesome!! All those features on one card! Amazing! This will really make the Mega PC open up.. How far away are you to finishing this and will you be making any for sale?

BTW, I vote my interest in you making a nice compilation of all your info etc on Mega PC 😀

-------------------------------------------------------------------------

Hey Zalog! I'm looking forward to having my own journey once I get my Mega PC back.. seeing other folks doing stuff with it is inspiring 😀 I think apart from it being oddball in design, the Megadrive being built in attracts attention too. When I bought it all them years ago the attraction was the MD and that it was so compact and cool looking.

I'm on the case with the battery. I have someone going to my aunts this week to get the base and undo it for me to see... I have a vague memory of infact replacing the battery as it didn't hold settings etc, maybe one of the reasons why it was going for £5.. I remember opening it and finding the original batt with the startings of leakage, fluff etc. But of course even the "new" batt is old now so it could have leaked too. The Alt12887 looks good, will that work in a 386 board too?

Thats really interesting about the Mega PC plus.. I thought they had used a 7486 board, but it just seems like Amstrad made a real rush job!... does the Cyrix program basically make it possible in software to use the L1 cache on upgraded Mega PC 386sx boards?.. i'm now wondering if changing the BIOSes to the plus versions would work, and be more stable (should I decide to upgrade the 386sx to a 486slc)

I'm now thinking if its possible to make a Mega PC plus out of my standard board (should it be leak free). Its not as good as the 7486slc.. yes like you say probably not much gains, but just a thought.. Hopefully the 486slc board turns up.. damn I hope I didn't throw it away!

Do you have a photo of the Mega PC plus 7386 board?

The ti chips.. yes I read how some of the 3.3v chips were run on the same process as the 5v so the difference was just expected tolerance.. so a bit risky, but some have done it and have no problems (yet). I saw the bridgeboard mod on amibay, it looks a bit untidy seeing the CPU like that. I prefer it to be neat really though so yes if I could find a 5V 486slc that would be nicer. Its just that right now there is a plethora of those G50 chips on ebay..

Looking forward to seeing your Mega PC running with the 5428!

Thanks for all the info, you guys rock! 😀