newbie needs help with A500 ntsc / pal issue

Hi!

I'm an Amiga noob, first post here, i did a lot of reading before i posted, but i need advice! So here is my issue:

Recently i bought an AMIGA 500 in like-new (well, almost ) condition. My only problem is that the machine is NTSC. I want to "change" it to PAL. I opened the case to check the mobo and the fat agnus, mobo is Rev5, agnus is 8370.

I did some search about the subject, so i know some info about the ntsc/pal switch, 8372a install, etc.

But i was thinking: my only goal is to change the machine to pal, and rev5 mobo-s came with hardcoded ntsc or pal chips... what if i just simply remove my 8370 (hardcoded to ntsc) and replace it with an 8371 (PAL) agnus? Will it work? Do i need to do other modifications? Is 8372a the only way to achieve ntsc / pal change or a simple replacement of chips like i thought is sufficient?

Please experts, share your wisdom with me!!

[DH]

You'll find some info here regarding the 8372A. Ignore the heading for the link http://eab.abime.net/support-hardwar...a500-rev5.html

[Jope]

If you just stick in a 8371, it will become a PAL machine. You should also replace the main oscillator to one used in PAL motherboards, but this is not strictly necessary. The video timings are a tiny bit off if you leave the NTSC oscillator in.

Thanks for the quick replies guys, been very helpful!
Jope, could you please elaborate a bit on this oscillator? I'm quite noob, and i dont know which one is the "main oscillator" you refer to. Also, what specs should i look for if i want to buy a PAL one...
Thanks!

[Jope]

The oscillator is the silver rectangular package with the text OSC silkscreened next to it. Right next to the big square Agnus chip:
http://www.bboah.com/download_photos/a500mb_rev6a_1.jpg

28.63636 MHz NTSC or 28.37516 Mhz for PAL

Wow, super-quick, super-helpful reply! Many thanks!

[pandy71]

Also required frequency can be provided trough video port (Pin 1 and Pin 2).

Thanks for the input pandy71, could you please elaborate a bit on this info? I don't quite understand how should I provide the required freqency trough video port?
Also, Jope, you wrote that the replacement of the oscillator is not strictly necessary... what will happen if I only stick in a 8371 Agnus? Will i experience problems? Note that i will only use my A500 for some games!
Thanks in advance!

[pandy71]

Originally Posted by inkalsecurity

Thanks for the input pandy71, could you please elaborate a bit on this info? I don't quite understand how should I provide the required freqency trough video port?

General idea is very simple - there is one external clock input ^XCLK - where any reasonable frequency can be feed to Amiga, and additional line ^XCLKEN which serve as switch between internal and external clock source.
Both lines are TTL level, and as ^XCLKEN is unbuffered and directly connected to Agnus then extremely caution is required when you connecting anything (same principle for bidirectional lines HSYNC and VSYNC used for genlocking purposes).

Simplest way is use same type of the XTAL generator (metal cane, 4 pins, 5V VCC, TTL levels), +5V Vcc for generator is taken from pin 23, GND is taken from pin 13, generator CLK output connected trough resistor (22 - 47 ohm) to pin 1, selection between internal/external CLK can be made in various ways - simplest is use resistor 22 - 47 ohm and connect this resistor from one side to pin 2 and from second side to pin 13 - as an alternative logic can be considered to switch between CLK sources (or replacing generator by programmable one even dynamic frequency change - overclocking, variable floppy speed - possibility to read/write not standard floppy disk formats).

[Jope]

Originally Posted by inkalsecurity

what will happen if I only stick in a 8371 Agnus? Will i experience problems? Note that i will only use my A500 for some games!
Thanks in advance!

Some video timing will be a bit off and perhaps some tightly coded trackloaders might fail?

Nothing drastic though, it doesn't hurt anything to run it with the NTSC clock.

Thanks again for the quick replies guys, this forum is very friendly and helpful!

Best regards

[pandy71]

Originally Posted by Jope

perhaps some tightly coded trackloaders might fail?

Less than 1% error - probably not even noticeable by MFM decoding (Europe/US floppies are interchangeable).
Video no longer valid timings but still inside typical TV tollerance.