A500 + A3000 Agnus 2MB chip RAM via trapdoor

cmorley · 05 August 2018, 11:11

So I've been asked about modifying my 2MB trapdoor RAM card for the A500 to provide 2MB chip RAM in conjunction with an A3000 Agnus on an Amiga 500 rev 6A.

I am well aware that this is an easy enough mod for those competent at soldering.

Doing it via the trapdoor slot makes the 2MB chip upgrade trivially reversible. Also very easy to install with basic soldering skills (A500 jumpers need configuring only).

This can (probably) already be achieved by desoldering (or cutting off) the PLD on my 2MB card and soldering a few links to connect RAS, CASL/H and DRA9 at the PLD pads to connect the A3000 Agnus signals to the RAM.

I could provide current boards without the PLD on to make this easier.... I could spin a new board easily enough... I could do a new board with different PLD code to allow using the mobo RAM as slow RAM.... I could do a 4MB board for 2MB chip RAM and 1.5MB slow RAM...

Lots of options. I could sell them tested, solder yourself kit/PCB only or DIY gerbers.

If you're doing this mod then you're probably fine soldering some DRAMs acquired from China so is there much point? I also don't have an A3000 Agnus for testing there are none on eBay. I myself would have no use for such a board since I'd just use my A500+ with 2MB chip & 1MB slow.

Thoughts?

watman · 06 August 2018, 10:33

A3000 Agnus is a rare sight, I doubt there will be a lot of people wanting to buy such card/kit, a guide to modifying existing board is probably a safest bet...

alexh · 06 August 2018, 10:54

Why would you do this?

The rev6a can be upgraded to 2MiB chip RAM by simply replacing the Agnus (Doesn't have to be an A3000 Agnus it can be 2MiB 8375 Agnus), changing some jumpers and replacing the 1MiB RAM with 2MiB RAM on the motherboard.

http://www.rasterline.com/images/ami..._2MEG_CHIP.jpg

If you want to reverse it you put the jumpers back, swap the Agnus and the RAM.

cmorley · 06 August 2018, 11:32

Quote:

Originally Posted by watman

A3000 Agnus is a rare sight, I doubt there will be a lot of people wanting to buy such card/kit, a guide to modifying existing board is probably a safest bet...

Yeah that is what I though. Guides already exist.

Quote:

Originally Posted by alexh

Why would you do this?

I was asked by someone.

Quote:

Originally Posted by alexh

The rev6a can be upgraded to 2MiB chip RAM by simply replacing the Agnus (Doesn't have to be an A3000 Agnus it can be 2MiB 8375 Agnus), changing some jumpers and replacing the 1MiB RAM with 2MiB RAM on the motherboard.

http://www.rasterline.com/images/ami..._2MEG_CHIP.jpg

If you want to reverse it you put the jumpers back, swap the Agnus and the RAM.

The A500+ and A600 8375 have different pinouts. It does have to be an A3000 Agnus as is mentioned in the JPG you linked. Swapping back is not trivial - desoldering RAM is a pain.

alexh · 06 August 2018, 11:52

Quote:

Originally Posted by cmorley

The A500+ and A600 8375 have different pinouts.

I don't think that is true. The PAL A500+ 390544-01 is AFAIK pin compatible with the PAL A600 318069-10 (and the same for the NTSC variants).

It was me (and Zetr0) who started compiling the information available today about different Agnus'.

Quote:

Originally Posted by cmorley

It does have to be an A3000 Agnus as is mentioned in the JPG you linked.

The JPG I linked to says you can use 8372B, 8372AB and 8375.

Quote:

Originally Posted by cmorley

Swapping back is not trivial - desoldering RAM is a pain.

Understood. I had thought the RAM was socketted.

cmorley · 06 August 2018, 12:20

Quote:

Originally Posted by alexh

I don't think that is true. The PAL A500+ 390544-01 is AFAIK pin compatible with the PAL A600 318069-10 (and the same for the NTSC variants).

The A500+ and A600 Agnus have different pinout to the A500 (rev 6A) Agnus. I could have worded that differently.

Quote:

Originally Posted by alexh

The JPG I linked to says you can use 8372B, 8372AB and 8375.

I don't think you can use any 8375, the JPG specifies 318069-19 or 318069-03

I went by your list http://eab.abime.net/showthread.php?t=21961

hlide · 06 August 2018, 14:18

@alexh

If you have a 318069-3 (PAL/NTSC), a 318069-18 (PAL, Vbb) or a 318069-19 (NTSC, Vbb) which are "compatible" with A500 rev6A/7, you need to remove the original 512Kx4bit RAMs and put 1MBx4 RAMs on the empty RAM slots due to the way how JP5 and JP3 are modded because N.C pin becomes A9 and /RAS1 becoming DRA9 goes only to the N.C pins (which are A9 for 1Mx4bit RAM) of the second RAM row (the one with empty RAM) and if you don't remove the first RAM row, DRA9 will go to /RAS which is wrong, hence "Swapping back is not trivial - desoldering RAM is a pain."

I have a 318069-18 - I can deal with jumpers mods (JP2, JP3, JP4, JP5 and JP7A) but I have no sockets on DRAM rows. And I happen to have the 2MB expansion card which may be helpful in this regard if I can swap the ram to get a full 2M chip RAM (with or without extra slow RAM coming from the original RAM).

The point is the card could be universal so it can be used for any Agnus (including A3000 ones). I could go by removing the PLD, add a socket to be able to revert by putting the PLD back or use pin header strips to connect the necessary wires to get an A3000 Agnus compatible card.

And yes, not many people would be concerned. I just think if that card could be more universal, it would be great.

Daedalus · 06 August 2018, 14:34

But is it not considered normal practice in general to add sockets for the RAM when doing mods like this? at least that's what I do. then you're not desoldering chips, just removing them from sockets. Once you've removed the original chips, there should be no more desoldering no matter what configuration you choose.

hlide · 06 August 2018, 14:57

Quote:

Originally Posted by Daedalus

But is it not considered normal practice in general to add sockets for the RAM when doing mods like this? at least that's what I do. then you're not desoldering chips, just removing them from sockets. Once you've removed the original chips, there should be no more desoldering no matter what configuration you choose.

Oh, I guess you have no idea how hard it is to find 1Mx4b RAM in DIP20 format in affordable price. On EBay, 4 x TC514400 --> above 56€. This article is becoming rare.

Sure I could find them in Ali Express - probably cheaper - but are they working TC514400 DIP20?

Mr.Flibble · 09 August 2018, 10:04

Quote:

Originally Posted by hlide

Oh, I guess you have no idea how hard it is to find 1Mx4b RAM in DIP20 format in affordable price. On EBay, 4 x TC514400 --> above 56€. This article is becoming rare.

Sure I could find them in Ali Express - probably cheaper - but are they working TC514400 DIP20?

There’s an adaptor board to convert the surface mount version over to DIP if that helps.

alexh · 09 August 2018, 11:17

Quote:

Originally Posted by Mr.Flibble

There’s an adaptor board to convert the surface mount version over to DIP if that helps.

Yeah nice.

It effectively doubles the price of the RAM but at approx £1/chip for SOJ 20-pin 1Mx4 DRAM (so £8 total for 4 chips inc adapters) it's hardly bank busting.

https://www.ebay.co.uk/itm/New-4x-Ad...-/122327379622

hlide · 09 August 2018, 22:15

Someone advised me to get those adaptors as well. Their prices were too high and their availabilities close to nil until I was given that link so I ordered them in case of.

Daedalus · 14 August 2018, 12:12

Quote:

Originally Posted by hlide

Oh, I guess you have no idea how hard it is to find 1Mx4b RAM in DIP20 format in affordable price. On EBay, 4 x TC514400 --> above 56€. This article is becoming rare.

Sure I could find them in Ali Express - probably cheaper - but are they working TC514400 DIP20?

I don't get the relevance of this post to what I said. Yep, the chips are rare, and I am actually aware of that, but that only make it even more sensible to fit sockets while you have the opportunity, then no more desoldering if you get faulty/fake chips or want to transfer them to another machine.

Marchie · 04 September 2018, 01:24

Those adapters are great, I was beginning to despair that, having finally found an 8372B for my A2000 I was now unable to find RAM!

Any tips on how to solder pins to them? (asking as a complete soldering amateur)

05 August 2018, 11:11	#1
cmorley Registered User Join Date: Jun 2018 Location: Oxford, UK Posts: 66	A500 + A3000 Agnus 2MB chip RAM via trapdoor So I've been asked about modifying my 2MB trapdoor RAM card for the A500 to provide 2MB chip RAM in conjunction with an A3000 Agnus on an Amiga 500 rev 6A. I am well aware that this is an easy enough mod for those competent at soldering. Doing it via the trapdoor slot makes the 2MB chip upgrade trivially reversible. Also very easy to install with basic soldering skills (A500 jumpers need configuring only). This can (probably) already be achieved by desoldering (or cutting off) the PLD on my 2MB card and soldering a few links to connect RAS, CASL/H and DRA9 at the PLD pads to connect the A3000 Agnus signals to the RAM. I could provide current boards without the PLD on to make this easier.... I could spin a new board easily enough... I could do a new board with different PLD code to allow using the mobo RAM as slow RAM.... I could do a 4MB board for 2MB chip RAM and 1.5MB slow RAM... Lots of options. I could sell them tested, solder yourself kit/PCB only or DIY gerbers. If you're doing this mod then you're probably fine soldering some DRAMs acquired from China so is there much point? I also don't have an A3000 Agnus for testing there are none on eBay. I myself would have no use for such a board since I'd just use my A500+ with 2MB chip & 1MB slow. Thoughts?

06 August 2018, 14:18	#7
hlide Registered User Join Date: Dec 2017 Location: VIGNEUX SUR SEINE Posts: 14	@alexh If you have a 318069-3 (PAL/NTSC), a 318069-18 (PAL, Vbb) or a 318069-19 (NTSC, Vbb) which are "compatible" with A500 rev6A/7, you need to remove the original 512Kx4bit RAMs and put 1MBx4 RAMs on the empty RAM slots due to the way how JP5 and JP3 are modded because N.C pin becomes A9 and /RAS1 becoming DRA9 goes only to the N.C pins (which are A9 for 1Mx4bit RAM) of the second RAM row (the one with empty RAM) and if you don't remove the first RAM row, DRA9 will go to /RAS which is wrong, hence "Swapping back is not trivial - desoldering RAM is a pain." I have a 318069-18 - I can deal with jumpers mods (JP2, JP3, JP4, JP5 and JP7A) but I have no sockets on DRAM rows. And I happen to have the 2MB expansion card which may be helpful in this regard if I can swap the ram to get a full 2M chip RAM (with or without extra slow RAM coming from the original RAM). The point is the card could be universal so it can be used for any Agnus (including A3000 ones). I could go by removing the PLD, add a socket to be able to revert by putting the PLD back or use pin header strips to connect the necessary wires to get an A3000 Agnus compatible card. And yes, not many people would be concerned. I just think if that card could be more universal, it would be great. Last edited by hlide; 06 August 2018 at 14:29.

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06 August 2018, 10:33	#2
watman Registered User Join Date: Apr 2018 Location: Poland Posts: 36	A3000 Agnus is a rare sight, I doubt there will be a lot of people wanting to buy such card/kit, a guide to modifying existing board is probably a safest bet...

06 August 2018, 10:54	#3
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,337	Why would you do this? The rev6a can be upgraded to 2MiB chip RAM by simply replacing the Agnus (Doesn't have to be an A3000 Agnus it can be 2MiB 8375 Agnus), changing some jumpers and replacing the 1MiB RAM with 2MiB RAM on the motherboard. http://www.rasterline.com/images/ami..._2MEG_CHIP.jpg If you want to reverse it you put the jumpers back, swap the Agnus and the RAM.

06 August 2018, 14:34	#8
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,334	But is it not considered normal practice in general to add sockets for the RAM when doing mods like this? at least that's what I do. then you're not desoldering chips, just removing them from sockets. Once you've removed the original chips, there should be no more desoldering no matter what configuration you choose.

09 August 2018, 22:15	#12
hlide Registered User Join Date: Dec 2017 Location: VIGNEUX SUR SEINE Posts: 14	Someone advised me to get those adaptors as well. Their prices were too high and their availabilities close to nil until I was given that link so I ordered them in case of.

04 September 2018, 01:24	#14
Marchie Registered User Join Date: Jul 2016 Location: Sydney / London Posts: 589	Those adapters are great, I was beginning to despair that, having finally found an 8372B for my A2000 I was now unable to find RAM! Any tips on how to solder pins to them? (asking as a complete soldering amateur)

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