Amiga 500 ++ replica + Diet Agnus adapter question

[turrican9]

So I soldered up five Amiga 500 ++ replica boards. 3 of them is using Agnus 8375 (2MB chip support)

The two last ones I make using the diet Agnus adapter in order to use Agnus 8372As (1MB chip support). Because I'm not willing to pay the insane prices the 8375s goes for now and I have plenty of 8372As laying around.

So I already made one using the Diet Agnus adapter with 1MB chip RAM on the adapter itself. I also made one with no RAM on it (supposed to use Amigas RAM) but that one failed (did a few mistakes). So I have more Diet Agnus adapters on order.

The question is, is there any point soldering on the trapdoor expansion connector with these 8372A setups? I cannot see one single reason to what I could use the trapdoor expansion for when I use 8372s in these two replica boards. Since the 8372A can only see 1MB chip RAM anyway.

[Jope]

Unless you plan to make a reslow circuit, you can just leave it out.

[seb132]

There are some boards on GitHub with mass storage and internet connection, I think. My memory might fail me but it’s not a big hassle to solder a connector, is it?

[LIV2]

As Jope said you can leave it out. RAS/CAS aren't connected to the motherboard by default. They can be passed through with the relevant jumpers on the bottom but I've never really thought to test that and don't know if they're useful at all off the top of my head.

[turrican9]

Originally Posted by LIV2

As Jope said you can leave it out. RAS/CAS aren't connected to the motherboard by default. They can be passed through with the relevant jumpers on the bottom but I've never really thought to test that and don't know if they're useful at all off the top of my head.

But you have tested the diet Agnus adapter with the jumpers set to Amiga RAM and no RAM on the adapter itself? Because the first diet agnus adapter I made was without the RAM on the adapter and the jumpers configured for Amiga RAM. I then populated the A500 ++ replica board with known good RAM. I got a green screen. I think I must have made a bridge or something when soldering the pins to the diet agnus adapter because I stuck them in so they touched the back of the Agnus socket instead of sticking them in just enough for them to hold. So I'm thinking too much solder may have flown along a pin and made a bridge on the back of the Agnus socket.

I have two more Diet Agnus adapters on the way and plan to make one of them with no RAM. So I need to be sure it should work using the Amiga RAM. So you never tested this?

[LIV2]

I should elaborate that I mean I haven't put much thought into the jumper configuration needed to make a trapdoor expansion work, but it should work fine with the onboard ram as long as all the Amigas memory chips are fitted.
The 500+/++ should be jumpered as default, rather than for the 1MB options set for Rev 8A 500's

[turrican9]

Originally Posted by LIV2

I should elaborate that I mean I haven't put much thought into the jumper configuration needed to make a trapdoor expansion work, but it should work fine with the onboard ram as long as all the Amigas memory chips are fitted.
The 500+/++ should be jumpered as default, rather than for the 1MB options set for Rev 8A 500's

So you don't think it would be possible to configure this A500 ++ board as a Rev 8A Amiga 500 with 512KB Chip and 512KB slow RAM from the trapdoor because the Diet Agnus adapter may be missing a few signals for it to work?

Anyway, my ACA 500 Plus can be configured to whatever I want really. So I can set 512KB slow RAM (coming from the ACA 500 Plus) leaving me with 1MB chip + 512KB slow RAM. With no need to have any slowram expansion in the trapdoor. So I can do those stubborn floppy games that requires slowram from trapdoor. Doing mostly whdload anyway.

I really prefer these A500 ++ replica boards over original A500 boards. All new solderjoints. All done by myself. All new sockets. Every chip is in a socket so easy to diagnose and repair. And it looks damn sexy.

And I must say that your Diet Agnus adapter looks very sexy aswell when paired with these boards.

[LIV2]

It may be possible to use 512K onboard and 512K in the trapdoor if you configured it as shown here, with the rams in U20,21,22,23, no U32 and with JP3 and the jumpers underneath U32 configured as shown in the attached image, you would still be able to use the slow ram option in your ACA too

[turrican9]

Originally Posted by LIV2

It may be possible to use 512K onboard and 512K in the trapdoor if you configured it as shown here, with the rams in U20,21,22,23, no U32 and with JP3 and the jumpers underneath U32 configured as shown in the attached image, you would still be able to use the slow ram option in your ACA too

What about JP2 and JP7A? As shown in this picture

This picture is from an 8A board configured from Commodore as a regular A500 (512 chip/512 slow)

[LIV2]

JP2 & JP7A set that way will configure as 512K chip + 512K slow, default JP2 & JP7A will configure as 1MB chip which is usually what you want

[turrican9]

Originally Posted by LIV2

JP2 & JP7A set that way will configure as 512K chip + 512K slow, default JP2 & JP7A will configure as 1MB chip which is usually what you want

yes, because I've seen guides on converting Rev 8a Amiga 500 boards to fully fledged Amiga 500 Plus boards. So I kinda knew about these jumpers.

I would say that 512KB chip/512KB slow and kickstart 1.2/1.3 is probably the best setup for floppy gaming. Some games require that slow ram from trapdoor to work.

Since I have almost done five replica boards now where 3 of them are using 8375 Agnus with 2MB chip, the one pictured in my first post is using the 8372A and 1MB chip I was thinking the last one could be configured as a regular Amiga 500 with 512 Chip/512 slow. But at the same time that would force me to cut a small trace between the bottom pads at JP2. Something I am not keen on doing on these fine looking boards.

I almost always use my A500s with either the ACA 500 or ACA 500 Plus anyway. Both the ACA 500 and ACA 500 Plus will convert trapdoor RAM into chip RAM without doing any jumpers on the motherboard. As long as it's 8372A Agnus. And the ACA 500 Plus can add 512KB slow RAM.

[turrican9]

Finally made a working Diet Agnus Adapter with no RAM on it. Really took my time with this one and made sure everything was done properly. Using glasses, magnifying glass and a headlamp. The jumpers to switch over to Amiga RAM are really small and I really had to take my time to cut them without damaging the PCB.

With regards to setting one of these replica boards up like a standard Amiga 500 with 512 chip/512 slow I've voted against it. Reason being I need to cut several traces between pads. Also at the JP3 location two of the pads are painted over (not there) on these replica boards. Which would involve not only having to cut the traces between both missing and the pads that are there but also reconfigure the missing pads elsewhere with a bodge wire. Also, I really don't want to cut traces in general on these replica boards.

One nice thing using the Diet Agnus adapter with RAM on it VS the one without is not only that you don't need any of the RAM chips from U16 to U23 but can also leave out U34, U35 and U32 logic chips. That is 11 chips which can be left out.

This picture is of course showing the Diet Agnus adapter with no RAM on it. Using Amiga RAM. The picture in my first post is the other Diet Agnus adapter with RAM on it. I will solder one last Diet Agnus adapter with RAM on it. Have some smd RAM chips on order from China. Nice way to use some of my 8372As. And very practical with the pin socket so I can swap the Diet Agnus adapters out easily with no soldering required.

[turrican9]

With regards to converting the replica board to a stock A500 with 512 chip/512 slow. Based on pictures I've seen of Rev 8A. A500 boards. Aside from cutting the connection between the two lower pads at JP3 and blobbing the two upper pads together, blobbing the pads at U32 and blobbing the two right most pads at JP7A I edited a picture of what I think I would have to do for JP3 on the replica boards. Because of the two missing jumper pads.

Correct me if I'm wrong please. This is what I have been able to gather by studying pictures from the A500 Rev. 8A boards.

Edit: Maybe the jumper pads are under the PCB solder mask? And just scratching would reaveal the pads under there? Removing the need for that bodge wire