Some photo's from the testing...

Myst via Win3.1 works ! - the CD ROM drive struggles during the startup video, but the game itself plays fine and looks good . This is certainly a result as my attempt with the old 5420 graphics chip found it was very difficult to play - now the only limitation with MYST is how fast the Backpack CDROM is - the only solution would be running a drive from the IDE, but I'm not going to do that to this system, so the Backpack will have to do.

Other games such as Warcraft 2 play nicely and "talkie" adventure games are fine with the CD drive and perform flawlessly.

However I did get some sound issues with the AWE64 card with some games (especially Civilisation) when no sound, or even adlib (from the Megadrive) was heard. I was a bit suspicious about the pnp - so tried a non-pnp card. A quick change to a old Aztech Sound Galaxy card fixed it and all is working ok now. I'm probably going to leave everything else alone until Keropi's MegaPC card becomes avaliable, as the PC side is running well and I don't want to jinx it 😀

I had no idea "CL5428 scam" was a thing... wow!
atleast Zalog you got the memory boost and full 1MB support which is more important than gui acceleration features IMHO since the system is a bottleneck anyways

smsdave wrote on 2020-08-15, 22:42:

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[...]

My electronics skills are very rusty; I'm hoping to attach an external battery pack with 3xAAA batteries to the Ext Bat pins which I understand should work ok despite the original battery only being 3.6V, does anyone advise against that with the voltage difference?

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-batteries-in-old-pcs/ and how the pins for the original battery also behave but I would value a second opinion.
[...]

Welcome aboard! I am away for the weekend but I can answer the EXT.BATT. connector: yes 3xAAA will work and provide 3.6v to the motherboard for the cmos/clock just fine. External battery headers on mobos this age assume NON rechargeable batteries so you are good to go! If you can wait until tomorrow I can post a pic indicating the +/- pins on the external battery connector.

About the stock monitor - it is NOT perfect and cannot ever hope to be due to the way it's been made. Maybe there is an internal pot to fix bowing but tbh do not bother. What was more annoying to me is the horizontal linearity issue on megadrive mode which makes the screen on right side to be compressed. This can be somewhat fixed by replacing a capacitor in the monitor.

Stock is like this:

by replacing C521 with a 2.2uf 200v one (original was 470nf/200v and it's the S.Correction one for 15khz mode) you can get this result:

not perfect but there is no way to make it perfect and it's not noticeable during gameplay anymore.
With some luck soon those monitors will just be collection items and superior ones readily available can be used 😉

Zalog wrote on 2020-08-16, 12:57:

Welcome - seems like we're gathering a fair number of the megapc owners here on vogons 😉 In answer to your questions - Don't know what type of external battery you'll be using, but if it's a lithum or other non-rechargeable, you'll definitely need to have a diode in the link to the motherboard otherwise the megapc will try and recharge the battery which is a no-no. If it's a rechargable then don't worry about this. There is a bit on adding an external battery on this video https://www.youtube.com/watch?v=6dWb-uw27Yg - can't remember which of the 4 video's its on, but you may find it helpful.

Glad the monitor idea is helpful - its certainly an improvement over the old monitor - don't worry my old one is permanently switched on too (!)

Thanks for the link, I'd seen that RetroManCave video (which is excellent and helped me no end) but rather than solder another connection in where the old battery was as he did, I'm actually planning on linking some regular AAA batteries up to the External Battery Pins on the motherboard as per attached photo to avoid any soldering mishaps.

I've got hold of one of these battery packs from ebay (https://www.ebay.co.uk/itm/4-5v-3xAAA-CMOS-RT … rd/174320997984) and with an extension cable I should be able to have the batteries themselves sit outside the main casing so I can remove them when it's not in use and avoid any risk of future leakage. It's the direction of how to attach the connector that I'm unsure of! I got the idea to look for it on the MegaPC motherboard from this discussion: http://www.vcfed.org/forum/archive/index.php/t-30683.html

Dave

@smsdave
correct me if I am wrong but from the pic I see the right-most pin connecting to R27 and then D7 (that is a charging blocking diode)
so if this is truly the case then the right-most pin is the (+) side

since you have a multimeter it's easy to find the (-) pin since it's ground: so pick a ground place and see what pin has direct connection to it

keropi wrote on 2020-08-16, 18:27:

@smsdave correct me if I am wrong but from the pic I see the right-most pin connecting to R27 and then D7 (that is a charging bl […]
Show full quote

@smsdave
correct me if I am wrong but from the pic I see the right-most pin connecting to R27 and then D7 (that is a charging blocking diode)
so if this is truly the case then the right-most pin is the (+) side

since you have a multimeter it's easy to find the (-) pin since it's ground: so pick a ground place and see what pin has direct connection to it

Thanks, that's the corroboration I was looking for; testing one probe on a motherboard mount screw and the other on that left most pin gave near enough 0 ohm resistance so I've just attached the leads and the machine is now keeping BIOS settings for the first time since I acquired it. Hurray! Attached photos show the connector attached and the battery box on an extension cable for anyone else who's trying something similar in future. I'll just need to find a hole in the casing to thread that lead through.

I was fascinated by those screen tests on the megadrive you posted; where did you get the ROM image from for that as I'd love to try it on mine with my everdrive? I'd noticed it was badly off as I really felt it playing Sonic 2 earlier but didn't realise just how bad it actually was until I saw your screenshots!

?

yep, it's the 240p test suite for megadrive: http://junkerhq.net/xrgb/index.php?title=240p … is.2FMega_Drive
glad the external battery works 😁

all monitors have the same issue, you can even see it on the ads/reviews for the system back then 🤣
just see how compressed that right-most palm tree is compared to the others:

Some news on my side. I managed to dump the BIOS of the PC7486SLC80 using another method as the NSSI one proved not to be reliable (it only dumps a part of it). I removed both high and low BIOS chips and used a TL866II-Plus to dump their contents. Both chips were properly identified by keropi as AM27C512. This is what I came up with (also included is an interleaved file from the 2 dumps).

Edit: It turns out the chips were ST M27C512 instead, as they now dump even with "Check ID" ticked without any error. I also tried multiple redumps of both chips and all my dumps were byte-wise identical. Just in case it interests someone, I used the Xgpro software that came with the programmer.

Dioxaz wrote on 2020-08-26, 19:13:

Some news on my side. I managed to dump the BIOS of the PC7486SLC80 using another method as the NSSI one proved not to be reliable (it only dumps a part of it). I removed both high and low BIOS chips and used a TL866II-Plus to dump their contents. Both chips were properly identified by keropi as AM27C512. This is what I came up with (also included is an interleaved file from the 2 dumps).

thanks for sharing this! yes this should work just fine - I will try it tomorrow evening on the 386sx board , it should boot without issues

keropi wrote on 2020-08-26, 19:30:

thanks for sharing this! yes this should work just fine - I will try it tomorrow evening on the 386sx board , it should boot without issues

Very exciting news 😀 - have everything crossed that all goes well for you keropi and we get to see a what an stock original megapc plus could do performance wise 👍. It shoulds be a very interesting comparison and perhaps explain another bit of amstrad history 🤔

Well I do not expect much in terms of performance increase, the 486slc was used by amstrad as a selling gimmick because it had 486 in the name... benchmarks will show good improvement due to that 1kb of internal cache but real-life performance is not that drastically different.
I once had a 486slc2 upgrade on my IBM 386sx , maybe it gave it a 10~15% boost at best.
There are later and better 486slc made by IBM, those are really incredible and closer to a 486DX in terms of performance but they also need L2 cache to shine. It's too bad we can't source them - but even if we did maybe they are all 3.3v parts so a simple swap would not be possible...
at any rate - still awesome 😁 +10% is +10% in the end 🤣

Oh I forgot to update on the situation, the 386sx mobo does not boot even with the properly dumped BIOS.
Dioxaz made another dump this time with the correct eprom model but as expected nothing was different.
My theory is that you need that gate A20 patch-wire as that kbc pin is directly connected to the chipset (it was just easier to solder on that pin I guess)
I have not tried it though - maybe when the 486slc cpus arrive I'll give it a shot

By the way, since you seem to own flash carts, there's a small homebrew scene for the Mega Drive/Genesis ..
Project MD looks quite nice, for example.
A few commercial games, like Pier Solar or Tanglewood were also made recently.
(Betas and demos can be downloaded free of charge still. )

On top of that, a basic compiler, BasiEgaXorz, may run on Win9x (Win95).
So in theory, you could write and run programs directly on the Mega PC.

A parallel to SD adapter then could be used to transfer files to the SD card the flash cartridge uses..
Provided, that it is compatible to Windows 95.
Windows might switching inputs/outputs, which could cause trouble with LPT ports. Some modifications might be necessary, perhaps.
MicroProject - MicroSD to LPT Printer Port

My story has a little progress. I finally got my Auntie to drag my Mega PC out of her garage and pass to my step dad to check it out. She says the monitor has certainly been thrown away (by accident) along with some other old PC monitors and towers previosly used by my cousin about 2 years ago... damn! And all that seems to be left of my 7486slc is the user manual... so I guess thats been thrown too... double damn! But whats left looks in reasonably nice condition!

The battery has been removed finally, and it looked like gunk has spread on the board near it and under the FDD and HDD connectors... I can't see so well from the pictures sent to me, but it looks like corrosion is minimal to not so bad... my step dad cleaned it best he could with lemon juice but I fear there could be hidden damage under the HDD/FDD connectors..

Here's some pics..

Jo22 wrote on 2020-09-02, 16:24:

By the way, since you seem to own flash carts, there's a small homebrew scene for the Mega Drive/Genesis ..
Project MD looks quite nice, for example.
A few commercial games, like Pier Solar or Tanglewood were also made recently.

Yes, have been supporting these projects - its nice to have original carts for the new Tanglewood and XenoCrisis games - these new Megadrive games look (and sound !) really good on the Mega PC !

Actually I have been thinking about the MegaSD flash cart (https://shop.terraonion.com/en/products/16-me … _cartridge.html) - its a pretty interesting piece of kit since it would let us play MegaCD games on the MegaPC without the uber rare connector cable ! Still at the price it is at the moment, I'm having to save my pennies to get one !!

Krikzz has a superior product available than the MegaSD card now, I suggest you look at this instead :
https://krikzz.com/store/home/59-mega-everdrive-pro.html

phipscube wrote on 2020-09-08, 10:40:

My story has a little progress. I finally got my Auntie to drag my Mega PC out of her garage and pass to my step dad to check it out. She says the monitor has certainly been thrown away (by accident) along with some other old PC monitors and towers previosly used by my cousin about 2 years ago... damn! And all that seems to be left of my 7486slc is the user manual... so I guess thats been thrown too... double damn! But whats left looks in reasonably nice condition!

The battery has been removed finally, and it looked like gunk has spread on the board near it and under the FDD and HDD connectors... I can't see so well from the pictures sent to me, but it looks like corrosion is minimal to not so bad... my step dad cleaned it best he could with lemon juice but I fear there could be hidden damage under the HDD/FDD connectors..

Your MegaPC looks in great shape 😀 it is a really nice clean example - pity the monitor and 7486slc have been chucked - still with the Benq monitor discovery at least what is left will still be very usable. Yes definitely do check and clean beneath the HDD and FDD connectors if your able - the leak on my late 386 board definitely went under there and had done nasty damage by the time I'd got hold of it.

Some minor progress to report from me - I have added a small dual CF to 2.5" IDE upgrade !

this is attached using a basic 44pin to 40pin connector cable which connects the power feed as well - all autodetects nicely and tested with my usual 256MB CF card.
I then swapped in two 512MB cards to bring the total storage up to the massive total of 1GB which is pretty much all you can get in without a BIOS overlay or XTIDE.
When installed in the chassis using a 2.5" to 3.5" drive rail adaptor, its a neat fit and a hardly observable addition.

All running nicely now, with lots of free space for games - but also noticed one additional benefit - the PC is quieter as the only moving part now is the PSU fan !! 😀

Tiido wrote on 2020-09-09, 12:40:

Krikzz has a superior product available than the MegaSD card now, I suggest you look at this instead :
https://krikzz.com/store/home/59-mega-everdrive-pro.html

Ooooh, thanks Tiido that is interesting - and a little bit cheaper, so I won't have to save as many pennies too 😀 !

Zalog wrote on 2020-09-09, 12:46:

Ooooh, thanks Tiido that is interesting - and a little bit cheaper, so I won't have to save as many pennies too 😀 !

quite a bit cheaper I must add, no DHL shipping and no DHL import fees on top

I've got one of these flash carts (no name), too.
Just recently, I was able to run some SMS games on it when inserting the cassette in a Model 1..
This makes me wonder - does the Mega PC still allow the Z80 CPU to be the primary processor?
I don't mean to start an off-topic discussion, I'm simply curious. 😅
- Because some later Mega Drive units from TecToy didn't allow this anymore. Or so I heard. Phantasy Star 1 for Genesis was essentially the Master System game (with a built-in adapter) also.