Problem with memory expansion?

[Zac67]

If the gurus with both expansions are the same (or very similar) the mainboard and/or the Agnus socket seems to be the problem.

You'll need to open the case and take a look at the trapdoor connector - possibly some of the acid damage has spread over there and some cleaning/resoldering is required. Additionally, the Agnus socket can become unreliable with old age and improper storage. I may have to pull out the Agnus chip to inspect/clean the contacts - make sure you use a PLCC puller (~3€). Levering with a screwdriver can very quickly break the socket, especially with age.

Ah yes: the RAM address lines come from Agnus (it's the RAM controller for chip RAM). The data lines run through some latches (U10-U13) to the CPU side. (The latch is the point where the busses can be deconnected to run independently: chipset side and CPU/fast side.)

[turrican9]

Hello. Sorry for posting in this old thread but I had almost the exact same problems on a Rev. 6A Amiga 500 motherboard. Only when the memory expansion was plugged in. I tried several different memory expansions that I know works.

One example was when loading a cracked version of The Chaos engine from cold boot. After the cracktro the game stopped loading and most of the time the Amiga would reset and show a guru. If I then clicked the left mouse button and loaded again the game would load up fine. However, if I turned the PSU off and left it off for 5 seconds or more the same guru thing would happen again or game loading would just lock up. I also left Silkworm running in demo mode a whole night and woke up to a guru. Street Rod cracked version would very often crash with a guru after I passed the copy protection by clicking one of the colours/numbers there. Also, when leaving the garage the driving scene would not be there. It would skip directly to the city. And there was something strange about the music.

And I tested this games in my other Amigas where they were completely fine. And again, this only happened if I had a RAM expansion card plugged in.

Yesterday I searched up the mod that can turn the trapdoor memory into chip RAM, to see if that would make any difference. What I discovered was that the chip RAM mod was already done on this board. lol. I then undid the mod and now everything works perfectly fine! Got this Amiga from a friend which had bought it on ebay.

So I thought this was worth mentioning if someone else has similar problems. Just check if the chip RAM mod is used and try and undo it. Here is the link to show how to mod/unmod trapdoor RAM into chip mem for 6A motherboards

[Oldsmobile_Mike]

The chip ram mod should be fine to do, and is generally beneficial - the only exception might be with old software that's expecting fast memory in that address space, or I suppose if you try to do the mod and don't have the right Agnus chip installed, or have done it wrong some other way.

I'd point the finger more at all those cracked versions of games you mention trying, rather than anything else. I bet if you boot it to Workbench it would be perfectly stable.

Also, you might want to look into either a Gotek or WHDLoad for your miggy. Floppies suck. lol

[turrican9]

The chip ram mod should be fine to do, and is generally beneficial - the only exception might be with old software that's expecting fast memory in that address space, or I suppose if you try to do the mod and don't have the right Agnus chip installed, or have done it wrong some other way.

I'd point the finger more at all those cracked versions of games you mention trying, rather than anything else. I bet if you boot it to Workbench it would be perfectly stable.

Also, you might want to look into either a Gotek or WHDLoad for your miggy. Floppies suck. lol

Hey there, yes Workbench worked fine. I have Several Goteks and tried with those too. The mod was done correctly and it has the right Agnus. I already have one other Amiga 500 which has ACA 500 + fully upgraded ACA 1221. ACA 500 will automatically turn trapdoor mem into chip ram on this setup. As long as it's Rev. 6A or newer. I also have Amiga 1200 with ACA 1233 and Amiga 600 with ACA 620. But I like to load floppy games out of nostalgia. I have over 300 fully working DD diskettes which are verified. But somtimes I like to use my other Amiga 500 which has two Goteks, for floppy games. I have alot to choose from.