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Offline AndrewPTopic starter

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A500 GVP HD+ Memory Expansion Issues
« on: March 15, 2023, 03:06:25 PM »
Hi everyone,

long time Amiga owner here, I've got an A500 which I've been using for a few years with no issues. Full Spec is A500 Rev 6, 1MB Chip RAM, 1.5MB Slow RAM (via a 2MB trapdoor expansion and the chip ram mod), Dual 1.3 and 3.1 ROMS,HDMI output via a Pi and a GOTEK floppy emulator. I recently added a A500 GVP HD+ 40mb drive with WB 3.1 installed. This boots and works absolutely fine.

However, I recently added a couple of 1MB 30 pin SIMMS to the GVP (2MB total) and can't get them to run. They were apparently tested ok. When the machine boots it goes straight in the Amiga Expansion Board Diagnostic with the red screen and tells me the SCSI controller board is OK (Board 1, Manufacturer 2017, Product 11) but the Memory board is defective (Board 2, Manufacturer 2017, Product 10). The jumper settings have been triple checked, I've cleaned both ram contacts and the GVP ram pins as well as the sidecar bus on the A500 with IPA, the version 4.13 ROM in the GVP is seated correctly and I've checked the SCSI lead to the HDD.

Bizarrely, in Workbench 3.1, SYSINFO->Boards and the Autoconfig tools both tell me they can see the RAM board in the GVP (the Product and Manufacturer numbers all match) and that it is populated with 2MB ram so I'm now quite confused...

I've reached the limit of my knowledge and googling the issue hasn't turned up anything extra. Any advice as to what if anything I can try next? Many thanks.
 

Offline Matt_H

Re: A500 GVP HD+ Memory Expansion Issues
« Reply #1 on: March 15, 2023, 05:36:10 PM »
Welcome!

Are the RAM jumpers set correctly? http://amiga.resource.cx/exp/impact500mk2
That page also mentions an incompatibility with trapdoor fast RAM expansions (which it sounds like you have). Not sure what the alluded fix is, however.
 

Offline AndrewPTopic starter

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Re: A500 GVP HD+ Memory Expansion Issues
« Reply #2 on: March 15, 2023, 08:58:03 PM »
Hi Matt, thank you for the welcome, much appreciated  :)

The jumpers are definitely set correctly. Based on what you said though, I disconnected the 2mb trapdoor expansion so there was just 512kb chip ram and verified this in Sysinfo. I then connected up the GVP then rebooted the machine. No change in the errors and only the 512kb was shown in Sysinfo.

Just to check, I then moved the GVP jumpers to the 4MB position (despite only the 2MB being fitted) and Sysinfo reports the memory to still be 512kb but in the 'boards' tab it shows 4MB....meaning Sysinfo is detecting the ram board and the jumper settings but not the memory itself.

Based on this and the info in the page you linked to, I think either both sticks of ram are faulty, or the chip ram mod to the Gary chip is causing the errors, since the board is being detected in Sysinfo (but not in the Expansion Diagnostic Tool on boot though). The page also mentions cutting a trace to fix it, but doesn't give any further details sadly.
 

Offline Matt_H

Re: A500 GVP HD+ Memory Expansion Issues
« Reply #3 on: March 16, 2023, 08:16:23 PM »
Hmmm. Seems like the next diagnostic step would be to try some different sticks of RAM in the GVP. Or different slots? I imagine the RAM needs to be inserted in a specific order.
 

Offline Motormouth

Re: A500 GVP HD+ Memory Expansion Issues
« Reply #4 on: March 16, 2023, 11:39:32 PM »
Mmmm.  Other than Jumper 2 for the 1 meg chip ram mod, what else has been done? any mods to the Gary?

is your mod something like this
http://www.boobip.com/hardware/A500_2MB

if so you may need to try removing the gary adapter and put the trapdoor ram back in.  The 2MB trapdoor expansion will act like it is 0.5 meg expansion (the gary will not know anything else is there)

The fast ram in the GVP will be accessed rather than the slow ram (mapped as fast ram) in the trapdoor.

Just FYI the GVP fast ram should be faster than trapdoor slow ram mounted as fast ram) anyway.
 

Offline AndrewPTopic starter

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Re: A500 GVP HD+ Memory Expansion Issues
« Reply #5 on: March 20, 2023, 05:29:42 PM »
Sorry for the late reply, thank you both.

The only mod is to Gary to give 1mb chip ram. I think it's a good idea to reverse this as you suggest and if that doesn't work, I'll try some new ram in the GVP> Will report back....
 

Offline Motormouth

Re: A500 GVP HD+ Memory Expansion Issues
« Reply #6 on: March 20, 2023, 08:35:06 PM »
Sorry
To be specific about this
The one meg chip mod should be on the A500 motherboard itself near the 68000, jumper 2
https://www.amibay.com/threads/a500-r6a-1mb-chip-ram-modification-caution-dialup-users-excessive-h-w-pr0n.4984/
This allows 0.5 the regular slow memory to be to added to the 0.5 meg on board to get 1 meg chip.
up to $0FFFFF
http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node00D3.html

As for the gary adapter, I am wondering if it allowing some of the trap door ram to added to the 8 meg auto config space
ie $200000 - 9FFFFF    8 MB Auto-config space

you could check this with sysinfo or another utility.

FYI slow-fast ram is usually mapped at  $C00000

It might be useful to look your ram mapping.

Regular Fast Ram (ie the GVP HD8 ram goes to the 8 MB auto-config space)

I have an GVP HD8 on my main A500, and an IDE Ad540 on one of my other A500s (which is a large trapdoor memory expansion with a gary mod plug in)
However your trapdoor expansion might be different which is why I would look at the address space with sysinfo


« Last Edit: March 20, 2023, 09:33:08 PM by Motormouth »