Amiga 500 rev 5 Chip ram mod issues

[Tony Gunk]

Hello again,

So I have this Boobip 2MB chip ram expansion for my amiga 500 that I'm attempting to install, and I'm having some issues with attempting to solder a wire to JP2 on the motherboard to connect to the expansion. Basically, I cut the connection from the bottom and middle pads and soldered the wire to the top and middle as instructed, but this causes a grey screen on boot up.

I fixed this by removing the wire and applying solder between the bottom and middle pads to reconnect them, but obviously this negates the point of the upgrade. Can someone tell me what I'm doing wrong and how to fix it?

Thanks

[Jope]

So you're talking about the Boobip trapdoor card + gary adapter?

In order to get 1MB of Chip in a rev 5 board, you must have a 1MB ECS Agnus (8372) fitted. Do you have that?

If not, you need to configure the trapdoor card as 1.5MB slow.

[Nbdy]

THe wire soldered to the JP2 is only in the middle, both upper and lower are empty and not connected ....

[Tony Gunk]

Originally Posted by Jope

So you're talking about the Boobip trapdoor card + gary adapter?

In order to get 1MB of Chip in a rev 5 board, you must have a 1MB ECS Agnus (8372) fitted. Do you have that?

If not, you need to configure the trapdoor card as 1.5MB slow.

I do have the ECS Agnus chip installed

[Tony Gunk]

Originally Posted by Nbdy

THe wire soldered to the JP2 is only in the middle, both upper and lower are empty and not connected ....

Everywhere I had seen talk of the top two pads being connected, but I'll try that and see if it works

[offog]

With these kinds of expansions using a board in the Gary socket, you definitely don't want to connect the top two pads of JP2 together - the wire just goes to the centre pad. (The outer two pads on JP2 are the A23 and A19 address lines from the CPU, both of which also go to the Gary socket, so there'd be no need for the wire if the pads were connected.)

[Tony Gunk]

Originally Posted by Jope

So you're talking about the Boobip trapdoor card + gary adapter?

In order to get 1MB of Chip in a rev 5 board, you must have a 1MB ECS Agnus (8372) fitted. Do you have that?

If not, you need to configure the trapdoor card as 1.5MB slow.

Okay so I have a problem, I was attempting to solder the wire to JP2 and the little pads on the jumper lifted off. What can I do now??

Do you know of anyone who can service it on the US?? I don't think I can make this repair myself...

[offog]

The centre pad of JP2 is only connected to the A19 pin on the Agnus chip - have a look at the the schematic in the service manual. You can see where exactly it goes in the great visualisation of the A500 PCB on amigapcb.org, although that's a Rev 8A PCB rather than Rev 5 - click on the pad and it'll show you which pin it's connected to.

I wouldn't worry about repairing the pad - just solder the wire to the appropriate pin of the Agnus socket on the underside of the board instead. The wire you've got may well be long enough to reach already, if you run it through the corner of the trapdoor slot near the Gary chip. Add a little fresh solder to the pin first so you can make a good joint quickly - you'll probably find it's easier to do this than it was to solder to the pad, since there's less stuff in the way!

[Tony Gunk]

Originally Posted by offog

The centre pad of JP2 is only connected to the A19 pin on the Agnus chip - have a look at the the schematic in the service manual. You can see where exactly it goes in the great visualisation of the A500 PCB on amigapcb.org, although that's a Rev 8A PCB rather than Rev 5 - click on the pad and it'll show you which pin it's connected to.

I wouldn't worry about repairing the pad - just solder the wire to the appropriate pin of the Agnus socket on the underside of the board instead. The wire you've got may well be long enough to reach already, if you run it through the corner of the trapdoor slot near the Gary chip. Add a little fresh solder to the pin first so you can make a good joint quickly - you'll probably find it's easier to do this than it was to solder to the pad, since there's less stuff in the way!

Thanks for the reply, hopefully I have a wire long enough to do it... Also the top pad of JP2 came off as well, what should I do about that one??

Also, where can get wire to work on this stuff if I need it??

[offog]

You can do the same if you need to connect to the top or bottom pad - use the schematic to find a pin on another chip that it's connected to. A19/A23 are both available on the CPU and on Gary. So you don't need to do anything about the top/bottom pads for now, but if you wanted to remove the expansion in the future, you could replace the missing jumper with a short wire on the underside between the appropriate pins of the Agnus and CPU (or Gary) sockets.

You can buy various kinds of wire in reels from electronics suppliers, but if you only need a few cm then you can recycle it. For repairing PCBs I like to use thin, solid-core wire - Ethernet cable is a good impromptu source of this, and you can hold it in place with a drop of superglue. If the wire needs some flexibility, use thin multi-stranded wire instead - if you can find an old printer cable or ribbon cable then the cores from that will probably do the job.

[Tony Gunk]

Originally Posted by offog

You can do the same if you need to connect to the top or bottom pad - use the schematic to find a pin on another chip that it's connected to. A19/A23 are both available on the CPU and on Gary. So you don't need to do anything about the top/bottom pads for now, but if you wanted to remove the expansion in the future, you could replace the missing jumper with a short wire on the underside between the appropriate pins of the Agnus and CPU (or Gary) sockets.

You can buy various kinds of wire in reels from electronics suppliers, but if you only need a few cm then you can recycle it. For repairing PCBs I like to use thin, solid-core wire - Ethernet cable is a good impromptu source of this, and you can hold it in place with a drop of superglue. If the wire needs some flexibility, use thin multi-stranded wire instead - if you can find an old printer cable or ribbon cable then the cores from that will probably do the job.

So just to clarify, for the sake of the ram expansion, all I need to do is solder the wire from A19 on the Agnus chip and connect it to the expansion, without having to make any other patches between the CPU, Agnus or Gary in regards to the top jumper?

[offog]

Yes, that should be correct. The top and bottom pads on JP2 don't need to be connected to anything with the expansion installed, so it doesn't matter if they're missing.

[Nbdy]

Do you read what we have written ....

From the gary adapter you should solder the wire to the middle pad of JP2, you don't need the upper and the bottm pad at all ...

[Tony Gunk]

Originally Posted by offog

Yes, that should be correct. The top and bottom pads on JP2 don't need to be connected to anything with the expansion installed, so it doesn't matter if they're missing.

Alright thanks, I'll reply here again once I have an update or if I need more help with this issue

[Tony Gunk]

UPDATE: I got the wire going from A19 (pin 59) on the Agnus socket to my expansion my Amiga now works and has the full 2MB from the expansion. Thank you guys a bunch for the help, I really thought I trashed my beloved A500 this time and I wouldn't have been able to figure it out with the advice.

[offog]

Excellent! Glad to hear you've got it working - I've found having the extra chunk of slow RAM is very handy in my A500s.