Amiga 500 rev8a.1 motherboard

Sim085 · 22 June 2021, 15:20

So while trying to solve an issue with an A500+ I have I bought another A500 motherboard, a rev8a.1, the one which is labelled A500+ but only has 512KB of ChipRAM on it.

I moved the chips from the broken A500+ (CPU, Kickstart, Agnus, Denise, Paula, CIAs), and another chip from an A500 (Gary).

It boots ok to Workbench, and everything looks good.

I then tried to install the +1MB ChipRAM board that was on my A500+, I booted but floppy disk did not work, and got artifacts on the "Insert Floppy Disk" screen. I said to myself probably jumpers are set so that it works with a +512KB ChipRAM board, so pulled one off from an A500 and tried that. The thing does not even boot.

Anyone with experience with this particular motherboard knows what is going on?

I never had one so zero experience. I know an A500 ChipRAM board does not work with an A500+ and vice-versa, but what is expected by this particular board?

chucsmom69 · 22 June 2021, 18:23

I am in the same boat - I have a 500 that is the rev8a.1 but if i put a 1meg expansion in the trapdoor the machine acts funky, if I use a 512k expansion it all works great but then I only have 1 meg chip instead 1.5

Jope · 23 June 2021, 10:44

You need to add one TTL chip, populate the missing RAM and reconfigure a few solder blob jumpers for the 512k board to become compatible with the 1MB trapdoor card.

chucsmom69 · 23 June 2021, 16:06

is that the only way? because thats beyond my skill set.

ovale · 23 June 2021, 17:44

https://retrocomputing.stackexchange...door-expansion

Sim085 · 23 June 2021, 20:48

However, if I wanted to leave it as is, why can't I neither use a +1MB ChipRAM expansion (which works fine with a normal A500+) and neither a +512KB ChipRAM expansion (which works fine with a normal A500)

?

Jope · 24 June 2021, 06:38

A 512k one should work fine. I guess you double checked that the connector was centered on both rows of pins?

22 June 2021, 15:20	#1
Sim085 Registered User Join Date: Apr 2009 Location: N/A Posts: 962	Amiga 500 rev8a.1 motherboard So while trying to solve an issue with an A500+ I have I bought another A500 motherboard, a rev8a.1, the one which is labelled A500+ but only has 512KB of ChipRAM on it. I moved the chips from the broken A500+ (CPU, Kickstart, Agnus, Denise, Paula, CIAs), and another chip from an A500 (Gary). It boots ok to Workbench, and everything looks good. I then tried to install the +1MB ChipRAM board that was on my A500+, I booted but floppy disk did not work, and got artifacts on the "Insert Floppy Disk" screen. I said to myself probably jumpers are set so that it works with a +512KB ChipRAM board, so pulled one off from an A500 and tried that. The thing does not even boot. Anyone with experience with this particular motherboard knows what is going on? I never had one so zero experience. I know an A500 ChipRAM board does not work with an A500+ and vice-versa, but what is expected by this particular board?

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22 June 2021, 18:23	#2
chucsmom69 Registered User Join Date: Apr 2021 Location: willenhall Posts: 86	I am in the same boat - I have a 500 that is the rev8a.1 but if i put a 1meg expansion in the trapdoor the machine acts funky, if I use a 512k expansion it all works great but then I only have 1 meg chip instead 1.5

23 June 2021, 10:44	#3
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	You need to add one TTL chip, populate the missing RAM and reconfigure a few solder blob jumpers for the 512k board to become compatible with the 1MB trapdoor card.

23 June 2021, 16:06	#4
chucsmom69 Registered User Join Date: Apr 2021 Location: willenhall Posts: 86	is that the only way? because thats beyond my skill set.

23 June 2021, 17:44	#5
ovale Registered User Join Date: Jun 2014 Location: milan / italy Posts: 174	https://retrocomputing.stackexchange...door-expansion

23 June 2021, 20:48	#6
Sim085 Registered User Join Date: Apr 2009 Location: N/A Posts: 962	However, if I wanted to leave it as is, why can't I neither use a +1MB ChipRAM expansion (which works fine with a normal A500+) and neither a +512KB ChipRAM expansion (which works fine with a normal A500) ?

24 June 2021, 06:38	#7
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	A 512k one should work fine. I guess you double checked that the connector was centered on both rows of pins?

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