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Old 23 May 2018, 01:34   #1
boratintheuk
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Question Converting NTSC A500 rev 5 to PAL

I've read that you can convert a rev 5 A500 from NTSC to PAL by grounding pin 41 on Fat Agnus. Will this allow me to run PAL software without issue or are there still other constraints on the NTSC machine? I'm also using one of those cheap GBS-8200 as my scan doubler and a PAL compatible display.

Thanks!
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Old 23 May 2018, 02:02   #2
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the clock rate will still be a little bit to high, because the crystal is still the same after your mod.
So your A500 will output some pseudo-PAL with some inaccurate timings - PAL software should all work, but some old video-hardware might not.

But try software-switching first - with a tool like this:

http://aminet.net/package/util/misc/SwitchInst130
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Old 23 May 2018, 02:26   #3
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Thanks, Gorf for the info. Forgive my ignorance, I'm still an Amiga noob in a lot of ways, but does a tool like that have to ran from Workbench? If it does how would I be able run other software from floppy? Sorry if this is a dumb question, I was just wondering how I would do that with all of Workbench loaded into RAM. Or can it run without Workbench? AFAIK Amiga doesn't have something like autoexec like in DOS. Correct me if I'm wrong here. Sorry for asking things that are pretty much common knowledge for Amiga-heads.
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Old 23 May 2018, 11:07   #4
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Depends on which version of the Agnus you have. 8370 = not switchable in hardware or software, install a 8371 (not switchable either, but stuck on PAL) or 8372 (hw and sw switchable) instead.

Ground pin 41 on a 8372 = NTSC, NC = PAL.

You should get the right oscillator too if you end up dedicating a machine for PAL use.
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Old 23 May 2018, 13:30   #5
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Quote:
Originally Posted by boratintheuk View Post
Thanks, Gorf for the info. Forgive my ignorance, I'm still an Amiga noob in a lot of ways, but does a tool like that have to ran from Workbench? If it does how would I be able run other software from floppy?
the tool i posted modifies the boot-block of disk.
So it is the first thing that gets executed. No matter of you are going to start WB or a game from that disk.

There are other tools, you can run later e.g. via icon for WB as well...

Quote:
Or can it run without Workbench?
yes - with or without.

Quote:
AFAIK Amiga doesn't have something like autoexec like in DOS.
That now is a different story, but AmigaOS has the startup-sequence in the "S" drawer in your Workbench (or many other system-friendly boot disks.)
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Old 23 May 2018, 17:10   #6
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Quote:
Originally Posted by Gorf View Post
the tool i posted modifies the boot-block of disk.
Which would render any decent game useless, as their use their own bootblock/are not DOS disks.
(That's a great tool I didn't know of btw, though, for when you can actually change the bootblock. Thanks for the pointer!)

So yeah disconnecting pin 41 might be the best option IF you have the Fat Agnus chip that allows it. Put tape over that pin and re-insert it in socket. Presto, your Amiga now boots in PAL (but can still be changed to NTSC via software). As for the crystal, I thought that was used to generate RF/Composite signals, and would not matter for RGB at all. Maybe I am wrong though.

Personally I installed a switch recently and now the switch doesn't work anymore and am not sure what happened. My machine is stuck in PAL and nobody seems to be able to help with this matter.
For most people though, directly converting to boot to PAL is the best option, as most software runs in PAL machines.

For switching to/from PAL<>NTSC via software, I recommend these simple commandline tools:
http://aminet.net/package/util/boot/TINYpalntsc

You can invoke them from the startup-sequence that Gorf mentioned, or at any Amiga CLI window, and they will change your screen to the desired mode.

Last edited by Akira; 23 May 2018 at 17:17.
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Old 23 May 2018, 21:18   #7
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The whole system runs off the same oscillator, so it is not 100% the same as a PAL machine. I guess if we had some kind of speed running scene, this would be more relevant. It is only a tiny bit off, so it's barely noticeable.
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Old 23 May 2018, 21:37   #8
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Quote:
Originally Posted by Jope View Post
Depends on which version of the Agnus you have. 8370 = not switchable in hardware or software, install a 8371 (not switchable either, but stuck on PAL) or 8372 (hw and sw switchable) instead.

Ground pin 41 on a 8372 = NTSC, NC = PAL.

You should get the right oscillator too if you end up dedicating a machine for PAL use.
Turns out I have an 8370. Unfortunate! Thanks.
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Old 23 May 2018, 21:45   #9
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I can find the 8371 online for pretty cheap so I might pick it up.

Can anyone tell me what kind of oscillator crystal I need? Can a novice with a soldering iron install it easily?
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Old 23 May 2018, 21:54   #10
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It is moderately easy to replace, a solder sucker pump or desoldering braid can be used to loosen up the old one. Don't pull it off until all legs move freely in the holes.

The oscillator is 28.63636MHz for NTSC and 28.37516 MHz for PAL. The easiest place to find a suitable oscillator is probably another Amiga.

Last edited by Jope; 23 May 2018 at 22:01.
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Old 26 May 2018, 22:01   #11
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Is the 28.37516 MHz crystal a part specifically made for the Amiga? Does anyone know if there's a general purpose version of that crystal? I'm having trouble finding the crystal online, unless I can find someone on here that will part with there's.
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Old 29 May 2018, 19:53   #12
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To change an Amiga properly between PAL & NTSC there are two parts to change,
the colorburst crystal, and the master oscillator, as well as setting the jumper to tell Agnus.
It’s the cloudburst crystal that could be ignored if it’s only RGB video that is needed.

The master oscillator is probably more made for analogue video devices than Amiga specifically,
since these frequencies are chosen because they are multiples of the video frequency the computer works with.
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Old 30 May 2018, 21:58   #13
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Is there a trick for removing Fat Agnus? Mine is in the socket so tightly than it nearly breaks my PLCC extractor. I don't want to damage anything.
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Old 30 May 2018, 22:37   #14
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I got the old chip out and was able to line up the new one and insert it. But this is what I'm greeted with when I power on

https://i.imgur.com/OuiVFaV.jpg

It looks like software is booting from the floppy with no problem, but this is the only picture I'm getting. The crystal still hasn't been replaced but that shouldn't be a problem should it?

I still need help with removing the chip too, this new 8371 is stuck even deeper than the first chip.
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Old 01 June 2018, 09:01   #15
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Has your HP monitor been verified to sync to 50Hz or does your scan converter also perform a vertical frequency boost?
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Old 03 June 2018, 02:01   #16
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Red face

Quote:
Originally Posted by Jope View Post
Has your HP monitor been verified to sync to 50Hz or does your scan converter also perform a vertical frequency boost?
It preforms vertical frequency boost as well, I had no picture issues until I inserted the 8371 Agnus.
The 8370 worked fine. Does the clock speed of the Amiga matter for the composite sync? My scan converter/doubler only uses the composite sync for RGB.


Could it be the cloudburst crystal? Is the timing on the composite sync tied to the cloudburst crystal?


Also I haven't been able to troubleshoot with the 8370 because the 8371 is in the socket so tightly I'm afraid of ruining the chip carrier.

I have one of these PLCC extractors but it still won't come out.

https://www.amazon.com/SMAKN%C2%AE-P...plcc+extractor

It's on the cheaper side. It slips out with too much pressure. Is my extractor the wrong size? Or just a cheap product?

Thanks for the help everyone

Last edited by boratintheuk; 03 June 2018 at 02:08.
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Old 04 June 2018, 10:20   #17
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The chip just gets stuck so hard in there. :-/

It's not possible for the extractor's hooks to be much wider than that, else they wouldn't fit through the slots in the corners of the socket.

You can try pushing down on the chip a bit first, to see if this helps in dislodging it, then insert the extractor and start rocking it around in a circular motion.

The colourburst shouldn't be a thing in this case, as RGBS doesn't have that, it's a composite/s-video related signal.
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Old 04 June 2018, 14:43   #18
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On the underside of Agnus are two holes. If you get really desperate you can carefully push Agnus using those holes. I have done it with a flat headed screwdriver.

It will require removing the shielding from the bottom of the A500.
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Old 06 June 2018, 06:24   #19
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I managed to pop out Agnus without having to use the holes. Is there any sort electronic lubricant that won't ruin the socket that I can for easier removal?
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Old 06 June 2018, 07:41   #20
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I think I ruined the Agnus chip carrier... I got the 8370 back in there and I still just get a grey screen, although software is booting.

Some of the black teeth that divide the contacts on the carrier have been damaged. The slot in the top left is also damaged but I wouldn't think that would be an issue? Here's a very large picture of it. I marked in red where the damaged teeth are.

https://i.imgur.com/oHrdpCV.jpg

It may look like some other teeth are damaged but it's just my camera. It isn't meant for this sort of macro photography.

Could this be the problem? Is there a solution without buying a new chip carrier? I don't think I have the soldering skills to install a new one...



C
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