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Thread: Upgrading the Amstrad Mega PC

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    Thank you for responding to my question once again

    Quote Originally Posted by modem7 View Post
    In this application, it is a straight replacement - remove 3.6V Ni-CD then replace with 3.6V Ni-MH.


    The "blocking" is only describing what function the diode is being used for.
    One of the following cheap/common diodes will do: 1N4001 or 1N4002 or 1N4003 or 1N4004.


    No.

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    I have installed the cr2032 battery holder with a diode and it works perfect. Thanks for your help.

  3. #13
    Join Date
    Dec 2005
    Location
    Toronto ON Canada
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    6,806

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    Quote Originally Posted by limboy777 View Post
    Thank you for replying.

    Option A -Can i replace a NICD with ANIMH with any other modifications i.e blocking diode
    I assume you meant "without" instead of "with"? If so, yes, as Modem7 said.

    Option B - What does a blocking diode look like? Do I need one if I put in a rechargable cr2032?
    It won't be a CR2032 if it's rechargeable.

    I use 3.6V NiCd or NiMH cordless phone batteries to replace rechargeable CMOS batteries; $2.00 in any dollar store around here, and easy to mount off-board just in case they do leak some day.

  4. Default

    Quote Originally Posted by MikeS View Post
    I assume you meant "without" instead of "with"? If so, yes, as Modem7 said.

    It won't be a CR2032 if it's rechargeable.

    I use 3.6V NiCd or NiMH cordless phone batteries to replace rechargeable CMOS batteries; $2.00 in any dollar store around here, and easy to mount off-board just in case they do leak some day.
    Thanks Mike

    I installed the cr2032 with a diode and have also found some custom made cr2032 holders with built in diodes for old comuters that I use for my other two vintage computers.

  5. #15
    Join Date
    Jul 2003
    Location
    Västerås, Sweden
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    6,270

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    Perhaps I should have a go at my battery as well. Only that I expect it to be an evening worth just to disassemble and get the motherboard out to more easily work on it.
    Anders Carlsson

  6. #16

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    Hello

    I recently purchased a Mega PC as well and I'd love to upgrade it, to have the 16MB of Ram, a 486 processor and even the SVGA graphic memory chips.
    - About the ram simms, Ive been searching ebay and found these: 161019153517, can I use them? They say with parity (or should I use without parity?);
    - The Cyrix processor can be this one on ebay: 271804876675? (Does it require soldering?)
    - And which SVGA memory chip should I acquire?

    Thanks in advance! And long lives the Mega PC!!!!

  7. #17

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    Let's resurrect this thread for a 2nd time:

    I just picked up a Mega PC, am in the process of getting it configured to my liking. Unlike many people, I had no problem with the CMOS battery: no explosion, no leaking - not even a drop. Of course I immediately snipped out the long-dead battery. I've read about quite a few Mega PC owners soldering in either a new barrel battery or a CR2032 holder w/anti-recharging diode. I can't understand why someone would go to all that trouble, when I just lazily attached an AA-battery "kit" to the external battery input on the motherboard. Specifically, I'm using this one from Ultimateapple2 which they market for the Apple IIgs but obviously it has wider applications...

    https://www.ultimateapple2.com/catal...products_id=21

    I've also installed a 50MHz Cyrix 486 SRx2 "snap-in" upgrade (as I have the need for speed), Intel 387SX 16-25MHz coprocessor (just for kicks), 16MB system RAM and the video RAM upgrade. Before I put the machine into (hyper-)active use I'm going to install a little fan over the CPU, because that sucker runs HOT and the included heat sink won't fit (there's no clearance space under the FDD+HDD cage).

    Thing came complete w/original monitor, keyboard, mousey and manuals. Whoopiee!!! Like some other owners have reported, my monitor is finicky about turning on: the power button doesn't always stay locked in when pressed. Luckily once it does come on, it stays on. Other than that everything works like a charm. What a neat, quaint little machine. I'm glad I finally picked one up.

    All I really need now is a 60Hz mod for the Mega Drive side. Why? Because I'm a USA-ican who doesn't appreciate his games running ~17% slower than he's used to!

    I'm going to start doing some "hard core" [!] testing of the onboard Ad Lib support, to see if anything's different from the usual fare. I've already noticed that PCM playback thru the YM3812 either doesn't work at all, or works with hiccups: at least in the case of Super Fighter and Sango Fighter which are the only (of the few!) games I've thus far tested that actually bother to support this "feature." Using a real, authentic Ad Lib sound card, the PCM plays back 100% with no issues, 100% of the time. So... a curiousity at this point.

    Aaaaaaaaand that's about it for now. Where did all you other Mega PC owners scoot off to? In the words of Sebastian Krist, "Come back here."
    WANTED: 8-bit Pro Audio Spectrum (not PAS-16), Covox Sound Master, IBM 3D Sound PCMCIA
    Please contact me if you have any of these for sale!! Thanks.

  8. #18
    Join Date
    Sep 2016
    Location
    Melbourne, Australia
    Posts
    306

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    You will find a very short battery life with the type of diode you have used.
    Signal diodes typical have a forward voltage drop of .6V, that brings your battery voltage down to 3.0v at the RTC chip. RTC chips typically require a minimum of 2.8v to operate. So you have a .2v margin before you battery becomes useless.

    I would suggest you use a fr107 schottky barrier diode, they have a forward voltage drop of about .24v giving you a margin of over .5v on your battery life.

  9. #19

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    Update: My Mega PC's ISA Mega Drive card is now 60Hz modded thanks to Ronnie @ assemblergames.com, so I can now play games at the proper USA speed as God intended. I can confirm that the 60Hz mode displays fine on the bundled Amstrad monitor.

    I ended up installing a Sound Blaster CT-1350B with C/MS upgrade, as I didn't want to rob the PC side of DAC sound. I disabled the Sound Blaster's onboard Ad Lib chip and game port by way of jumpers, so as not to interfere with the Mega PC's native support for these.

    Not a bad system setup, don'cha think?
    WANTED: 8-bit Pro Audio Spectrum (not PAS-16), Covox Sound Master, IBM 3D Sound PCMCIA
    Please contact me if you have any of these for sale!! Thanks.

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