A500 NTSC/PAL switch

[Amiga1992]

I have been thinking about adding this switch because it seems relatively easy in my A500 model.

I have a Rev.5 NTSC board, but I am a bit confused about what kind of Agnus I have.

The Rev.6 schematics I downloaded say in Key Componeents that Fat Agnus number is 8370 or 8371, but I have an 8372A in a socket clearly labeled on the motherboard as "Fat Agnus". I also read somewhere in these boards about a 8375 Agnus.

So what is it that I have, then?

As for the mod itself, I just need to lift pin 41 and then connect that through a switch to the socket, or leave "lifted", right?

Figured that while I have it all open trying to fix the joystick port, I might as well perform this little upgrade.

[EzdineG]

Akira, you are correct about the pin 41 mod. I wouldn't do it if I were you though, as you can get the exact same functionality by using the early boot menu (2.0+) and choosing PAL/NTSC from there.

The timings won't be exactly the same either way, as PAL and NTSC machines use different speed oscillator crystals. As to the significance of this... I'll leave it to someone with a little more knowledge to answer.

[Amiga1992]

Originally Posted by EzdineG

you can get the exact same functionality by using the early boot menu (2.0+) and choosing PAL/NTSC from there.

That only applies if you have Kickstart 2.x+. Which I don't (and won't).

[EzdineG]

Originally Posted by Akira

That only applies if you have Kickstart 2.x+. Which I don't (and won't).

If you're primarily using the machine to boot game floppies (and therefore won't be able to take advantage of any of the degrader/switcher programs on aminet) then the hardware mod does indeed make sense.

[DrBong]

Originally Posted by Akira

I have been thinking about adding this switch because it seems relatively easy in my A500 model.

I have a Rev.5 NTSC board, but I am a bit confused about what kind of Agnus I have.

The Rev.6 schematics I downloaded say in Key Componeents that Fat Agnus number is 8370 or 8371, but I have an 8372A in a socket clearly labeled on the motherboard as "Fat Agnus". I also read somewhere in these boards about a 8375 Agnus.

The 8372A is a 1MB Fat Agnus (aka Fatter Agnus), which gives your A500 ECS capabilities. The 8375 is a 2MB Fat Agnus (aka Super Agnus) and was also present in some A500 set-ups, notably Rev. 8 A500s......but also were whacked on Rev. 6 A500s too IIRC, due to C='s habit of whacking new chips on older motherboards on the production line before new revision motherboards became available.

Anyway, if ever in doubt about chip revisions, something called The Old Big Chip List on Aminet provides good info on all manner of Amiga chips.....according to chip name/no. on the label and, even, C= part no. The guy who compiled it apparently used to work at C= and it's actually quite good value!

Here's also another thread that debates the merits of a NTSC-PAL switch that may or may not be handy for you. Good luck with it all!

http://eab.abime.net/showthread.php?t=83629

[Amiga1992]

Thanks for that chip list DrBong! Will come in handy.
Do I understand correctly that Fat Agnus allows the computer to address 1MB of Chip RAM (max) while Super Agnus allows me to address 2MB (A500+-like)?

So I guess I can go ahead and do this, if I could see anywhere, with photos, how to do it. I'm quite unsure on how to lift a pin of a chip of this type (always dealt with the "centipede-like" types before).

[DrBong]

Originally Posted by Akira

Thanks for that chip list DrBong! Will come in handy.
Do I understand correctly that Fat Agnus allows the computer to address 1MB of Chip RAM (max) while Super Agnus allows me to address 2MB (A500+-like)?

Spot-on! That's always been my understanding and the BBOAH - which has some nice pics of different Agnus revisions BTW - suggests as much too.....

http://www.bigbookofamigahardware.co...t.aspx?id=1478

[Amiga1992]

OK cool. I Don't need 2MB Chip so this is great. I want to keep this as compatible with old software as possible.
Also why I want the NTSC/PAL switch. I can't live life just playing Cinemaware games

[DrBong]

If you can swing it easily enough on a Rev. 5 motherboard mate, then yeh go for the NTSC-PAL switch. Less messing around with software solutions, which will definitely make life easier and more pleasurable in the long-run!

[Jope]

It's a bit of a pain to do on the rev 5, the test pin is not that easy to isolate from the motherboard and add a switch at the same time.

Add a piece of sticky tape on top of the pin and reinsert the Agnus to make it PAL and be happy with that, no-one needs an Amiga that boots into NTSC as default. ;-)

[Amiga1992]

Originally Posted by Jope

no-one needs an Amiga that boots into NTSC as default. ;-)

That's a fair point haha. But if I can add a switch it would be neat.
I know what you mean about being difficult, I wouldn't even know how to do it as it is now. As I said, no experience with this form factor of ICs. I don't even have a chip puller for this, I need to get one.

[idrougge]

Easiest way to extract Agnus is from below. Commodore have made a hole in the motherboard underneath the socket so you can push the chip out instead of lifting it.

[Amiga1992]

I'm going to buy a PLCC puller just to be sure, I don't want to mangle this just because I am lazy and not get the right tools!

About the switch itself, I thought it was enough to connect it to ground or leave it disconnected, but I read somewhere else I have to connect it to ground or to 5V through a 10K resistor. Which is it?

[Jope]

Ground = NTSC, float = PAL

[idrougge]

Originally Posted by Akira

I'm going to buy a PLCC puller just to be sure, I don't want to mangle this just because I am lazy and not get the right tools!

Pushing it out is actually safer than a puller in my experience.

[Amiga1992]

Originally Posted by idrougge

Pushing it out is actually safer than a puller in my experience.

OK guys, I tried to push that thing, but it won't budge. I pushed quite hard, and at some point I thought I could damage it so I stopped it.

Any tips about how to do this? It really seems stuck!

[dalek]

Get a friend to hold on to the socket and push it out from the bottom with something plastic like a pen tube - as idrougge said. If it's stuck that hard and you try the plcc extractor you'll just end up scratching or chipping the plastic package.

[Amiga1992]

I have no plcc extractor. I put the Motherboard on a flat surface and pushed with a chopstick 🤣. Then I realized I might damage the socket so instead i held the mb from the socket and pushed. Still stuck. What if it snaps in half?

[dalek]

Doubt it will snap in half - Agnus' are easy enough to get from elsewhere though. Another option might be to drop some isopropyl alcohol in between the pins of the socket and the IC legs and use something like a sewing needle to get in between the socket pins and legs to gently create a bit of space to break the bond. Not to much force as those as the socket legs can break and then you need to source a replacement socket.

[Amiga1992]

One more question, there are two holes below, is it ok to push from one or should i be pushing from both at once?

I might try the isopropyl route to give some lubrication, thanks for the tip!