Amstrad Mega PC / Amstrad Mega PC Plus

Discussion in 'Repair, Restoration, Conservation and Preservation' started by Shane McRetro, Mar 21, 2012.

  1. DeChief

    DeChief Rustled.

    Joined:
    Jan 25, 2014
    Messages:
    1,492
    Likes Received:
    543
    And what screen would that be? It sounds quite useful, I might want one too. :D
     
  2. Bad_Ad84

    Bad_Ad84 Keyboard Error: Press F1 to Continue

    Joined:
    May 26, 2011
    Messages:
    7,868
    Likes Received:
    808
    Most Tvs with hdmi input that I've came across work like that.

    I have one on my workbench for testing.
     
  3. DeChief

    DeChief Rustled.

    Joined:
    Jan 25, 2014
    Messages:
    1,492
    Likes Received:
    543
    I've yet to have a monitor or TV that supports both 15khz and 31khz.
     
  4. Bad_Ad84

    Bad_Ad84 Keyboard Error: Press F1 to Continue

    Joined:
    May 26, 2011
    Messages:
    7,868
    Likes Received:
    808
    Meant to say vga not hdmi.

    If a TV has vga, it has to support 31khz, if it has scart it has to support 15.

    The ones I've tried have worked on the vga port with both
     
  5. DeChief

    DeChief Rustled.

    Joined:
    Jan 25, 2014
    Messages:
    1,492
    Likes Received:
    543
    Wait, there are monitors with both VGA and SCART?
     
  6. Bad_Ad84

    Bad_Ad84 Keyboard Error: Press F1 to Continue

    Joined:
    May 26, 2011
    Messages:
    7,868
    Likes Received:
    808
    I said TV's
     
    DeChief likes this.
  7. Mr. Sound-About

    Mr. Sound-About Never let dreams die!

    Joined:
    Jan 15, 2005
    Messages:
    217
    Likes Received:
    17
    I was lucky enough to score them all in the same set. The seller did a horrendous job of packing it all: the monitor only had a thin layer of bubble wrap around it, and the box was coming apart at the seams when it arrived from the UK! :confused: But surprisingly everything was OK. Only two keycaps had come loose from the keyboard, and they snapped right back in.

    Speaking of the TeraDrive, have you modded it at all? I know several people have (allegedly) desoldered the 286 CPU and soldered in a socket. What I'm trying to figure out is if anyone has tried installing a "Make-it-486" (or equivalent) upgrade CPU. But none of the modders have responded to my PMs...
     
    DeChief likes this.
  8. DeChief

    DeChief Rustled.

    Joined:
    Jan 25, 2014
    Messages:
    1,492
    Likes Received:
    543
    :mad::mad: Hearing stories of how badly people package CRTs makes me so mad, I've had them show up smashed to bits before. Such a waste...

    I have a Kingston 386 upgrade that I'm planning to put in it, but my TeraDrive is currently down. The PSU blew up and I can't quite figure out why, it was dead when I got the machine and then I re-capped it, so maybe I put a capacitor in the wrong place? It worked fine for months after though...

    Anyway, I can't see a reason why a CPU upgrade wouldn't work. I don't know anyone who has actually done it yet but @Ronnie and I have both been wanting to upgrade ours for quite a while. :p I'm also planning to add two more ISA slots to my TeraDrive so that it can fit a soundcard, 2MB EMS ISA card (from LoTech), and an XT-IDE compact flash ISA card (also from LoTech). Additionally I'd like to figure out how to connect a regular 3.5" floppy drive, which shouldn't be too hard; I think the TeraDrive's 3.5" interface is the same as the one in one of my IBM PS/1 computers.

    By the way, I've got all of the manuals for it and I'm going to scan them at some point. According to @Ronnie the TeraDrive doesn't quite work properly with SoundBlaster cards, but the manual specifically mentions compatibility with AdLib.
     
  9. Ronnie

    Ronnie Spirited Member

    Joined:
    Sep 13, 2012
    Messages:
    120
    Likes Received:
    30
    I've done the mod and it works ( cpu transplant) . I have a 286 to 486 Evergreen technologies upgrade. The last thing I was trying to achieve was getting more ram out of the simm connectors but I only got halfway through (see this thread) : https://assemblergames.com/threads/sega-teradrive-simms-ram-upgrade-help-needed.62782/#post-899946 too bad photobucket got greedy :D

    The Teradrive PC side can be temperamental, it can be picky about certain things. It's wired and interacts with the Sega side more than we probably know of.

    I was the first to wire a second ISA slot to the machine 'cause I needed a sound card badly :p , Retroswim later on got his Teradrive and did the same thing:



    Wait what? you didn't know I did that ages ago? :eek:
    Don't you remember I was even trying to get a modern FDD to work on it?

    It works ok with some sound cards but some work better than others. I'd like to see that part of the manual with reference to Adlib because the Teradrive doesn't have the -12V -5V power lines that some of the early sound cards use (Adlib, SB2.0, etc) to begin with. There are ways to get around this of course.

    See my crappy vid below for some Teradrive SBPro2/composite video sample:

     
    Last edited: Nov 6, 2017
  10. Mr. Sound-About

    Mr. Sound-About Never let dreams die!

    Joined:
    Jan 15, 2005
    Messages:
    217
    Likes Received:
    17
    If you haven't already, please consider running TOPBENCH to benchmark your system, then update the database and send it to the program author. It's interesting to explore the database and see how some of the exotic systems, and unique upgrades perform.

    Jeez, sure sounds like it! :confused: In fact your very detailed comments make it sound like a total pain in the ass system to own. I was wondering if I should bother picking one up, but I think you just helped me make up my mind: NO.
     
  11. Dioxaz

    Dioxaz Member

    Joined:
    May 28, 2012
    Messages:
    11
    Likes Received:
    5
    Back from a deep sleep. Dug out and settled my Mega PC again after moving out and thus having much more room. I'm glad to inform that I found a valid solution for displaying both the PC and Mega Drive parts of the Mega PC on any kind of monitor. I tried many solutions, including a Gonbes 8200 (slightly blurry and imperfect line-doubling, even at 60Hz), an Extron DVS 304 (only games running at 256x224 and 256x192 would show a picture...) and a Wei-Ya ACV-011.

    It's the last one who gave me the best results. It can be ordered here ($50 with free shipping) among others: https://sintron-hk.com/Wei-ya-ACV-011-CGA-to-VGA-video-converter-P2699910.aspx

    What this unit does is clean line-doubling: 15KHz transformed into 31KHz. Results isn't perfect yet (picture distorted at the top and some interferences are to note sometimes) but picture looks really nice IMO. DIP switches settings that give the best results are setting 14, OOXO. Setting 16 is to avoid as the top of the picture gets funnelled and the picture randomly disappears for 1 or 2 seconds.

    Some pictures here: https://imgur.com/a/SrJhZ

    Also, I took the opportunity to upgrade my unit with an 486SLC motherboard too! Except... there's a little problem as this is an earlier revision with an identical layout to the original 386 one (same chips everywhere, including the Western Digital 90C11, but with the 512K of video RAM already built-in) and only running at 25MHz instead of 33. There is a performance increase but it's not as drastic. That "new" motherboard has some incompatibilities if using an SB16 Value sound card. You can't use low DMA at 1 or some games will play their sound effects with a stuck loop (I had to set it to 3). Another minor issue, the PLAY.EXE audio player (from the SB16 software itself) randomly crashes the machine when attempting to play a 16-bit WAV file after an 8-bit one now.

    The other good news is that my original battery didn't leak despite letting the machine off for way too long. The one from the 486SLC motherboard didn't leak either but was dead. I did my battery replacement job (with an Amigakit CR2032 holder) on the 486SLC one and left the original motherboard with no battery.

    For the info, the 486SLC motherboard comes from an Amstrad PC7486SLC80 base unit (where the 80 is the HDD capacity, not the clock speed!) I bought from eBey.

    I might add some other pictures to that album later. I also hope to upload a video of the whole disassembly, motherboard and battery replacement process but with my usual laziness, it's not that easy. :p

    Edit: Just thinking about it now, does anyone here happens to still have all the software pre-installed on the Mega PC's original hard drive? I'd like to put my hands on that cool front-end menu (there's a screenshot of it on the PC7386SX manual cover) and that tutorial that I used to play around with younger. The only thing I could find till now to download is Counterpoint (I still have the SVGA utility disks, as far as I remember).
     
    Last edited: Nov 17, 2017
    DeChief likes this.
  12. DeChief

    DeChief Rustled.

    Joined:
    Jan 25, 2014
    Messages:
    1,492
    Likes Received:
    543
    Neat converter! I might get one if this monitor that I just won on eBay turns out to not support 15 and 31khz, but I'm hopeful - it's a Microvitech branded monitor that was often rebranded for Acorn computers, and I believe for Amigas as well. I couldn't get a sound card working on my Mega PC's 486SLC board either, but I don't know if it's the same board as yours now that I think about it. I haven't used the damn thing in an eternity!
     
  13. saxabar

    saxabar Member

    Joined:
    Jan 13, 2011
    Messages:
    10
    Likes Received:
    2
    Wow, very well! Could you share how to mod it?
    Thanks
     
  14. DeChief

    DeChief Rustled.

    Joined:
    Jan 25, 2014
    Messages:
    1,492
    Likes Received:
    543
    The monitor arrived, and it works great! There's a chunk of colour missing in the top left of the monitor though, only in Mega Drive mode - PC mode works perfectly. It doesn't affect gameplay, just looks a bit odd. :p

    Yes, please! I was testing some Japanese MD games in it and it was painful trying to play Sonic 2, it needs modding...
     
    Last edited: Dec 7, 2017
  15. Dioxaz

    Dioxaz Member

    Joined:
    May 28, 2012
    Messages:
    11
    Likes Received:
    5
    That's great news. That's one more monitor to mark as Mega PC compliant.
    The Mega PC ISA card uses a Sega 315-5487 chip which is the same used on VA0 and VA1 Mega Drive II systems, VA7 Mega Drive I ones. So it has the same pinout, and according to the Mega PC service manual, it can be easily modded to output 60Hz (and perhaps CSYNC).

    I also discovered by tracing the PCB that you only have to dissolder a black wire on the upper lower part of the board to make it ouput 60Hz! I don't know if all Mega PC ISA card have that last minute fix, but I think it's worth to look at if you'd like to see your Mega PC running at 60Hz. Indeed, that transforms your machine into an American Genesis. I recommend putting a 50-60Hz switch in order to retain European games compatibility.

    Until I decide making that picture gallery I was talking about earlier, here are some old photos I made from 2008 to 2012. They show PCB close-ups and picture viewing while plugged to a CRT TV (using vga2tv and a CSYNC circuit): http://dioxaz.free.fr/download/index.php?dir=megapc/pics/

    I think the wire you have to dissolder in order to have 60Hz is the black one next to the Z80 CPU, as seen on photo P9010333.JPG. is the wire located on the lower part of the board and brdging R75 and C43, as shown on this picture (note, it's already dissoldered here): DSC_0291.JPG

    Edit: sorry I gave a wrong info earlier, I actually removed my board again to double-check and now it's correct
     
    Last edited: Dec 8, 2017 at 11:27 AM
    DeChief likes this.
  16. saxabar

    saxabar Member

    Joined:
    Jan 13, 2011
    Messages:
    10
    Likes Received:
    2
    Unfortunately it doesn't work, without the black wire is still 50hz
     
    DeChief likes this.
  17. Mr. Sound-About

    Mr. Sound-About Never let dreams die!

    Joined:
    Jan 15, 2005
    Messages:
    217
    Likes Received:
    17
    No, because I didn't do the mod myself. Quoted from my previous message (which in fact you quoted too):
    "My Mega PC's ISA Mega Drive card is now 60Hz modded thanks to Ronnie"
     
  18. DeChief

    DeChief Rustled.

    Joined:
    Jan 25, 2014
    Messages:
    1,492
    Likes Received:
    543
    Then can @Ronnie share how to mod it? :p
     
  19. Dioxaz

    Dioxaz Member

    Joined:
    May 28, 2012
    Messages:
    11
    Likes Received:
    5
    I'd like to know too. :p
    That black wire must trace to pin 46 on the Sega 315-5487 chip by following the PCB traces (pin 46 is labelled "NTSC" according the service manual). It was the case with mine. I don't know if all boards have that same quick fix. Also, I'll have to check again which exact wire have to be dissoldered (my memories might be off, but I don't remember being other wires on my board).
     
    DeChief likes this.
  20. Bad_Ad84

    Bad_Ad84 Keyboard Error: Press F1 to Continue

    Joined:
    May 26, 2011
    Messages:
    7,868
    Likes Received:
    808
    It could be that you need to connect it to VCC, otherwise it could just be floating.

    (so move wire from leg of capacitor its on, to the other leg)
     
    DeChief likes this.

Share This Page