31 March 2024, 19:17 | #1 |
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Amiga 500 rev 5 Chip ram mod issues
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 Last edited by Tony Gunk; 01 April 2024 at 07:25. |
01 April 2024, 08:53 | #2 |
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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. |
01 April 2024, 12:53 | #3 |
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THe wire soldered to the JP2 is only in the middle, both upper and lower are empty and not connected ....
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01 April 2024, 16:05 | #4 |
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I do have the ECS Agnus chip installed
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01 April 2024, 16:08 | #5 |
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01 April 2024, 17:01 | #6 |
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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.)
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02 April 2024, 22:19 | #7 | |
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Quote:
Do you know of anyone who can service it on the US?? I don't think I can make this repair myself... Last edited by Tony Gunk; 02 April 2024 at 22:34. |
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03 April 2024, 01:06 | #8 |
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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! |
03 April 2024, 04:11 | #9 | |
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Quote:
Also, where can get wire to work on this stuff if I need it?? |
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03 April 2024, 15:23 | #10 |
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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. |
03 April 2024, 16:00 | #11 | |
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Quote:
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03 April 2024, 17:15 | #12 |
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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.
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03 April 2024, 18:03 | #13 |
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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 ... |
03 April 2024, 20:40 | #14 |
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Alright thanks, I'll reply here again once I have an update or if I need more help with this issue
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05 April 2024, 08:33 | #15 |
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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.
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05 April 2024, 15:49 | #16 |
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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.
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