MegAChip - A500 agnus question

[arnljot]

Hi,

I have the DKB Software MegAChip for A2000/A500

My problem as a PAL user is that this version I have is fitted with the 8375 (318069-11 NTSC) Agnus, and not the 8375 (318069-10 PAL) Agnus.

I will be using the A500 with my SONY Flatscreen TV which I don't think can display NTSC.

Do I have to source up a PAL Agnus, and is it hard?

Manual for the thing here, see page 5.

Info here and here

[rkauer]

 Vesalia use to have all versions of Agnus to sell.

[arnljot]

They have the 1MB version, I need the 2MB version.

It's also most commenly that ebay have the 512k or 1MB version.

[alexh]

I've never seen one for sale for many many months.

It seems a shame to butcher an A600 for a 2Mbyte Agnus but they are your best source but you will have to desolder it. I've been looking out for a cheap "spares or repair" one for ages.

I do not think you can use any other 2Mbyte PAL Agnus other than the 318069-10 (i.e. a 390544-01 may not work)

Unless your MegAChip is for a CDTV... you're better off buying an A500 plus, A600 or A1200 and selling whatever it is you've got.

[arnljot]

The MegaChip takes the 84 pin PLCC chip(Socket), as you say. It will have to be the 318069-11 (NTSC) or the 318069-10 (PAL).

I will not butcher any Amiga. It's agains my belifs But I will swap if anyone can use the NTSC chip instead of their PAL one, perhaps some US amiga owners with a PAL machine?

Anyway, I am not still convinced that I need a PAL chip? Maybe the NTSC chip will work in my PAL A500, or will it make my PAL Amiga into a NTSC Amiga? Or will it simply just not work?

[alexh]

The 8375 390544-01 is also an 84-pin PLCC.

I think will work, but not correctly.

The Agnus is only a fraction of what makes an Amiga PAL or NTSC.

[Gilloo]

I have also Megachip and Agnus 8375 318069-11 NTSC on my A2000.
Agnus is not able to display anything. It's Denise job.

With a Super Denise chip 8373 R4 390433-02, you can be sure that NTSC mode is displayed correctly on PAL TV, because Denise uses RGB lines of the scart connector.

After, you can select your monitor, PAL or NTSC, or adapt a little program to switch.

[arnljot]

I think I'm reaching for straws here. But I think someone once said that one can "hack" the agnus by removing a pin. That it would change it from being NTSC to PAL. But I can't remember which way, or even find anywhere on the web to collaborate this.

Has anyone else heard this?

[arnljot]

This article is for the 8372A (part no: 318069-01). It is also 84 pin, so I might guess that pin 41 is the same on those two chips?

Read more here

Pin 41 of the Agnus socket which is earthed on all REV5 boards controls whether the A500 starts up in NTSC or PAL mode. When it is earthed the Obese Agnus initialises in NTSC Mode which means that all USA owners need to do is plug in the chip and they are in the correct mode. We on the other hand have to de-solder and remove the socket from the board to isolate pin 41 which is connected to earth on both sides of the board. This chip was designed in the USA!! Removing the socket is a difficult and laborious task so other methods of isolating pin 41 are possible. I DO NOT recommend trying to drill through the board as the two pins 41 and 42 are very close together, the trace between them is thick and there are thin tracks either side of it under the socket on the top of the board. Bending the contact on the socket is a possibility but make sure you get it right or you'll be removing the socket anyway. Placing a thin piece of hard plastic, eg mylar, between the pin and the contact is another possibility. By putting a SPST toggleswitch between pin 41 and earth it is possible to switch between NTSC and PAL on resetting the machine. This would give good compatibility with American software and for this reason and others DO NOT just break or cut pin 41 off the chip. Pin 41 is taken to a jumper pad on REV6A boards.

So it might seem that if I isolate pin 41 it will operate in PAL mode?

[darksun9210]

it would seem so, and i certainly hope so. i haven't got an 'ntsc' megachip to test with, otherwise i would have checked this out myself for my A500  :-)

it would be great if this works :-D

[meega]

arnljot wrote:

I will be using the A500 with my SONY Flatscreen TV which I don't think can display NTSC.

Are you sure it won't accept NTSC? Have you tried yet?

[countzero]

I'm sorry but the NTSC agnus simply won't work in your PAL machine (been there, done that). You also need to change your crystal to make your amiga fully NTSC. At least that's what I was told, but I never tried.

[arnljot]

@countzero
Even with the pin 41 hack?

@meega
It's a Sony KDL-40W2000, in the product spesification it says that it will take NTSC. But I haven never managed to get that to work. It just looses synch. But going NTSC with my A500 is not an option, since it's too much hacking on it to go that route. Buying an American A500 however is, if pin 41 hack doesn't work.

[orange]

I also think you should use RGB Scart, that way you skip PAL/NTSC and get best picture quality.

[countzero]

I don't think the pin 41 hack makes the agnus PAL magically. Probably it just asserts the agnus so that it will start in PAL mode.

Also using RGB scart doesn't mean you skip PAL/NTSC. A PAL amiga will still output PAL (50 Hz) and an NTSC amiga will output NTSC (60 Hz).