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Old 06 March 2020, 17:39   #1
manossg
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ACA500 plus question

Hello, fine Amiga people!

It is time for me to get myself a nice ACA500 plus!

But I found out that my trapdoor memory expansion is no longer recognised by the miggy. I removed the battery, but to no avail.

So, ACA500 plus' website claims that the card can add the trapdoor expansion even if the Amiga does not have one. Is that true and does it work? Has anybody here tried it?
Or should I buy myself another trapdoor expansion, until I repair the first one?
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Old 06 March 2020, 19:50   #2
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It will add c00000 ram, but this is not strictly trapdoor ram as it cannot be made into chip ram.
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Old 06 March 2020, 20:01   #3
manossg
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Quote:
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It will add c00000 ram, but this is not strictly trapdoor ram as it cannot be made into chip ram.
Thank you for your reply, Jope. Could you please explain to me if and how this will affect day-to-day performance, if I want to use my Amiga mainly for WHDLoad and the odd productivity software?
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Old 06 March 2020, 20:12   #4
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Check your Amiga 500 trapdoor memory expansion card for an enable/disable switch or jumper. It's possible that you've put the card into disabled mode.
Also check both the expansion card and your Amiga 500 for electrolyte leak damage (from either the old battery or old electrolytic capacitors)
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Old 06 March 2020, 20:19   #5
manossg
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Quote:
Originally Posted by jlin_au View Post
Check your Amiga 500 trapdoor memory expansion card for an enable/disable switch or jumper. It's possible that you've put the card into disabled mode.
Also check both the expansion card and your Amiga 500 for electrolyte leak damage (from either the old battery or old electrolytic capacitors)
Thank you, my friend, for your reply!

I have already checked both positions of the switch about 95639476398 times, but no luck.

I have removed the old battery and tried to clean the damage done by it (a bit of a mess, but hopefully nothing major), but no luck again. The capacitors look ok, so I didn't bother with them, but I will definitely give them another look.
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Old 06 March 2020, 20:33   #6
jlin_au
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The trapdoor expansion memory operates as it normally would (as slow ram) except it would be mapped starting at address c00000 hex.

The ACA500plus has its own 8MB of ram installed that will be added to the ram already accessible on the Amiga 500. This 8MB operates at the same speed as the ACA500plus CPU while the ACA500plu CPU must slow down (wait) to access any memory or devices within the Amiga 500 or trapdoor expansion slot.
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Old 06 March 2020, 20:43   #7
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Take lots of good pictures before starting so you have a record of what cap goes where and in what orientation when you install the replacements.

Remove all the electrolytic capacitors and clean where they were.

Melt new solder into old solder joints with good quality flux to lower the melting point of the old solder before you remove the solder and parts. Will make work easier and hopefully lessen chances of lifting pads and traces.

Check entire board for dark or dull solder joints, corroded or discolored pins and vias; its all evidence of electrolyte leakage and damage. Using a dark light may also help as the electrolyte may fluoresce under UV.
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Old 06 March 2020, 21:10   #8
manossg
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Quote:
Originally Posted by jlin_au View Post
The trapdoor expansion memory operates as it normally would (as slow ram) except it would be mapped starting at address c00000 hex.

The ACA500plus has its own 8MB of ram installed that will be added to the ram already accessible on the Amiga 500. This 8MB operates at the same speed as the ACA500plus CPU while the ACA500plu CPU must slow down (wait) to access any memory or devices within the Amiga 500 or trapdoor expansion slot.
So, if I understand, there will be no noticable difference in day to day performance of ACA500+ w/o trapdoor expansion compared to ACA500+ with trapdoor expansion?
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Old 06 March 2020, 21:13   #9
manossg
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Quote:
Originally Posted by jlin_au View Post
Take lots of good pictures before starting so you have a record of what cap goes where and in what orientation when you install the replacements.

Remove all the electrolytic capacitors and clean where they were.

Melt new solder into old solder joints with good quality flux to lower the melting point of the old solder before you remove the solder and parts. Will make work easier and hopefully lessen chances of lifting pads and traces.

Check entire board for dark or dull solder joints, corroded or discolored pins and vias; its all evidence of electrolyte leakage and damage. Using a dark light may also help as the electrolyte may fluoresce under UV.
So the capacitors may be the culprits. A nice project here, even though my skills with the solder are below beginner level.

I was thinking of using a multimeter to try and find the culprit, but I wouldn't know where to start, the circuit look like a maze!
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Old 06 March 2020, 21:40   #10
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Originally Posted by manossg View Post
So, if I understand, there will be no noticable difference in day to day performance of ACA500+ w/o trapdoor expansion compared to ACA500+ with trapdoor expansion?
From what I understand the trapdoor expansion allows to extend your chip ram to 1MB, which in turn is needed to run some WHDLoad games (not sure what percentage). From their site:
Quote:
This includes a new revolutionary method that can turn your 512k trapdoor memory expansion into chipram! If your Amiga is equipped with an ECS Agnus chip and said internal 512k memory expansion, you can turn your computer into a 1MByte-Chipram computer, just by selecting a menu item in the configuration menu of the ACA500plus! A lot of stock A500 computers with board revision 6 or higher have this exact configuration.
So, you'll also need to have the specific ECS Agnus motherboard for that to work. I'm no expert though, so maybe somebody else can clarify it further.
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Old 06 March 2020, 21:54   #11
manossg
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Originally Posted by dreadnought View Post
From what I understand the trapdoor expansion allows to extend your chip ram to 1MB, which in turn is needed to run some WHDLoad games (not sure what percentage). From their site:
So, you'll also need to have the specific ECS Agnus motherboard for that to work. I'm no expert though, so maybe somebody else can clarify it further.
Thanks, man, that's why I reach out to the community...wanted to make sure if I need to solve my expansion problem first or if I can have full functionality with ACA500+ and fix the expansion at my leisure.
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Old 07 March 2020, 16:12   #12
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You can have full functionality with ACA500+ and then fix/replace the expansion later at your leisure.
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Old 07 March 2020, 16:42   #13
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Well, I guess it depends how you look at it. If you can't have 1MB Chip Ram without the extension (and specific motherboard) then it's not a "full functionality". Question is, how much do you really need this.

I think I recall hearing that even if some WHDload games won't work without 1MB CR (some even need 2MB) then you can use native hdd installers, so it's a sort of a workaround. But, again, this may or may not be true. I'm ineterested myself, since I use my Amiga strictly for gaming.
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Old 07 March 2020, 17:13   #14
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Originally Posted by jlin_au View Post
You can have full functionality with ACA500+ and then fix/replace the expansion later at your leisure.
That would be simply awesome, I would not want get hasty and end up with a messed up expansion, or an extra but useless expansion, thanks!

Quote:
Originally Posted by dreadnought View Post
Well, I guess it depends how you look at it. If you can't have 1MB Chip Ram without the extension (and specific motherboard) then it's not a "full functionality". Question is, how much do you really need this.

I think I recall hearing that even if some WHDload games won't work without 1MB CR (some even need 2MB) then you can use native hdd installers, so it's a sort of a workaround. But, again, this may or may not be true. I'm ineterested myself, since I use my Amiga strictly for gaming.
Yes, I recall reading that myself, so I would also be very interested to learn about that. I guess that native hdd installers might be an excellent temporary solution, or even use adf2disk (or actually give in and get me a Gotek) for the games that don't support hdd installation.
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Old 07 March 2020, 17:42   #15
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It is possible to modify an Amiga 500 with a Rev6 or higher motherboard to have 1MB of chip ram installed on the motherboard and an extra 1MB of chip ram installed in the Trapdoor. A Fat Agnus version that supports the specific motherboard version must be installed.

Regardless of the Agnus version installed the memory installed in the trapdoor will only operate at a slow access speed regardless of it being used as chip or slow ram.
The standard 8MB ram installed in the ACA500plus will operate as fast ram for either the Amiga 500 or the ACA500plus CPU.

Not sure what relative speed the ACA500plus 8MB ram will operate at if an additional Amiga 1200 CPU card with its own ram on the card is plugged into the ACA500plus.
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Old 07 March 2020, 17:48   #16
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Quote:
Originally Posted by jlin_au View Post
It is possible to modify an Amiga 500 with a Rev6 or higher motherboard to have 1MB of chip ram installed on the motherboard and an extra 1MB of chip ram installed in the Trapdoor. A Fat Agnus version that supports the specific motherboard version must be installed.

Regardless of the Agnus version installed the memory installed in the trapdoor will only operate at a slow access speed regardless of it being used as chip or slow ram.
The standard 8MB ram installed in the ACA500plus will operate as fast ram for either the Amiga 500 or the ACA500plus CPU.

Not sure what relative speed the ACA500plus 8MB ram will operate at if an additional Amiga 1200 CPU card with its own ram on the card is plugged into the ACA500plus.
I thought the 6a motherboard didn't have the extra pin needed for 2M chip ram? I know the hack to install 1M on the motherboard but not how to install a second meg of chip mem...
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Old 07 March 2020, 17:54   #17
manossg
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Quote:
Originally Posted by jlin_au View Post
It is possible to modify an Amiga 500 with a Rev6 or higher motherboard to have 1MB of chip ram installed on the motherboard and an extra 1MB of chip ram installed in the Trapdoor. A Fat Agnus version that supports the specific motherboard version must be installed.

Regardless of the Agnus version installed the memory installed in the trapdoor will only operate at a slow access speed regardless of it being used as chip or slow ram.
That's good to know, if I get in a REALLY hackerish mode!

So, another question;
Let's forget WHDLoad for now...if I want to run 512chip+512slow games (ie Dungeon Master), will I be able to boot these from floppies with the ACA500+ even without the physical expansion installed?
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