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Re: Amstrad Mega PC

Posted on 2020-08-16, 12:57

I'm strugging to work out the +/- pins for the Ext Bat on the motherboard, using my aging multimeter, the resistance appears to be approx zero on pin 4 (furthest from the edge of the MoBo) which I think means that's negative? This is based on what I read at http://pc-restorer.com/replacing-cmos- …

Re: Amstrad Mega PC

Posted on 2020-08-13, 20:28

Hello there. I'm the one who made the post linked above. I've upgraded to a 486SLC33 motherboard since (the one with the CL5420 chip and AMI BIOS) but I still have the older PC7486SLC80 one. And the processor is indeed a Ti486SL 25Mhz as the following picture I've just taken of the naked …

Re: Amstrad Mega PC

Posted on 2020-08-12, 18:55

very interesting info Zalog about the 386sx board with a 486slc cpu... too bad we can't locate the correct bios - most likely the only change is the activation of the 1kb of cache LOL Looking into the whole issue has been a really interesting bit of Amstrad PC history, Indeed the whole of the later …

Re: Amstrad Mega PC

Posted on 2020-08-12, 18:20

I just watched him do the replacement and almost couldn't help talking and pointing at my screen... :D As for the fire, I'm thinking that was an exaggeration in the post before. When he turned it on, there didn't even seem to be any magic smoke. :) Agreed, my thinking is with these rare boards its …

Re: Amstrad Mega PC

Posted on 2020-08-12, 08:16

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 …

Re: Amstrad Mega PC

Posted on 2020-08-11, 08:05

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 …

Re: Amstrad Mega PC

Posted on 2020-07-22, 12:43

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 …

Re: Amstrad Mega PC

Posted on 2020-07-20, 09:11

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 …

Re: Amstrad Mega PC

Posted on 2020-07-18, 15:27

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 …

Re: Amstrad Mega PC

Posted on 2020-07-16, 18:15

line-in #2 stays ;) also: https://i.imgur.com/RZcc1Zjl.jpg 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 …

Re: Amstrad Mega PC

Posted on 2020-07-16, 07:15

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 …

Re: Amstrad Mega PC

Posted on 2020-07-15, 08:42

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 …

Re: Amstrad Mega PC

Posted on 2020-07-14, 20:36

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 …

Re: Amstrad Mega PC

Posted on 2020-07-14, 09:31

I also noticed on schematic the vga chip is marked as "CL-GD542x" and not GD5420 specifically like all other ICs... so they just went for the cheaper option apparently! That's good, looks like there should be no problem adding a 5428 then :D BTW have you noticed the artwork on the reverse of the …

Re: Amstrad Mega PC

Posted on 2020-07-13, 08:16

So have been busy over the weekend....... Dropped in a Cyrix FasMath 33Mhz Co-processor - unfortunately the Cyrix logo is a bit dull so it doesn't photo well :-( _20200710_073346.JPG Added on a nice gold coloured heatsink onto the 486SLC - things are running much cooler now and it does seem to make …

Re: Amstrad Mega PC

Posted on 2020-07-13, 08:05

Ah even photos like these are great! thanks! I see there are missing details anyways due to photocopy It makes sense they modified a 386SX design since the 486SLC will just work in place of a 386sx all it needs is bios to enable that 1kb of L1 LOL Thanks for the jumpers, I was wondering what JP12 …

Re: Amstrad Mega PC

Posted on 2020-07-13, 07:56

Jo22 wrote on 2020-07-10, 17:22: Wonderful thread! Thanks a lot for all the information and the pictures, too! 🙂👍 Glad your enjoying it - the MegaPC is a great machine to work on and good fun to play on too ! Filename DSC_2381.JPG File size 669.61 KiB Views 6551 views

Re: Amstrad Mega PC

Posted on 2020-07-09, 10:26

wait , what 7486SLC service manual you are talking about? share share share! :D Unfortunately I only have a printed out copy of the service manual DSC_2362.JPG Will have a look into scanning it, although it may take a little while to sort..... To help folk, here are a couple of quick phone snaps of …

Re: Amstrad Mega PC

Posted on 2020-07-08, 17:41

Yes those reserved pins are for 32bit access and lead to the empty vram sockets - but they are all connected on the board so this is why it will be possible to just replace with a better cirus chip Going to 2 mb will require too much soldering but a chip replace and 1mb would be easily achievable …

Re: Amstrad Mega PC

Posted on 2020-07-08, 14:15

ah you also researched the onboard 5420! I did some research though - it is possible in theory IMHO to replace the GD5420 to something better up to 5428 - the pins that connect to the 2nd ram bank to allow 32bit access are there - I have not checked about the MCA pins though - are they consistent …

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