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Old 09 January 2019, 18:42   #1
simon_m74
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Amiga 3000 low memory

I managed to kind of repair a non-working A3k the other night.

Original problem, green screen and blinking power LED.
After a google; Agnus fault.
Tried a couple of other agnus Ic`s I have, and found a working one.

YAY!

system boots to kickstart (3.1 v40.68) - BUT not booting to the Hdd.

So going on changing Ic`s.. I tried to change the Scsi WD chip... still no Hdd. Next I checked the schematics, and saw that the Scsi IC connects almost completely to Super-DMAC.

Super-DMAC changed and YAY again! - boots to Hdd

BUT>>>>

when I`m loading from the drive (its a Hdd from a Virtuality machine) it starts to load VR system programs up (inc a modified startup-sequence) - it complains that its low on memory.
So I typed `Loadwb` to see if I could see available memory, but it wouldn't -too low.

So, I have installed a total of 6mb ZIP`s - but still low on memory?

Any ideas?

Thanks

Simon
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Old 09 January 2019, 19:01   #2
indigolemon
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Try running 'avail' to get the memory stats?
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Old 09 January 2019, 19:06   #3
simon_m74
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I`ll try that tonight if it allows me.

I also just checked the manual, and apparently theres a jumper to set ram type or something?
I`ll check that too.
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Old 09 January 2019, 19:13   #4
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I'd guess at buffers for the hard drives eating ram, how many partitions is it loading? Have you checked in early startup?
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Old 10 January 2019, 00:16   #5
simon_m74
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I disconnected the Hdd & booted WB3.1 from floppy.
Tried swapping some zips around.
Removed zips, and put dips in from another amiga 3k
all shows zero fastram on `avail`
also tried swapping `Ramsey` with another.

Going to try the A3640 on it next

Any other ideas?

Last edited by simon_m74; 10 January 2019 at 00:27.
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Old 10 January 2019, 00:26   #6
simon_m74
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no change with A3640..
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Old 14 January 2019, 08:01   #7
lesta_smsc
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If is failing to detect any RAM then the likelihood is it is not seeing the RAM. Was there corrosion towards the RAM socket base? It may be worth tracing the tracks for the port...

Can you post pics of the board with close up of RAM?
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Old 14 January 2019, 18:40   #8
simon_m74
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I`ll take some photos tonight.
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Old 15 January 2019, 14:25   #9
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Ok... I `think` I have found the problem......

Chip Ram not reading properly.
Fast ram not reading at all.

Ramsey IC sends out `R_W` to the Chip & Fast ram, via U252 (XOR gate)

When R_W is HIGH from Ramsey - its LOW to Fastram, and HIGH to Chipram.
When R_W is LOW from Ramsey - its HIGH to Fastram, and LOW to Chipram.

This IC seems to set the `Output Enable` on the Fastram (when HIGH after U252) and sets the `direction` of the data on the ChipRam (either `read or write`).

So as this IC is quite integral to the Ram operations, I`m assuming this IC is the problem.
Only about £1 each...pity its not on a socket though!
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Old 16 January 2019, 21:55   #10
lesta_smsc
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But without chip RAM how did you boot to Workbench or shell? I assume you're referring to the add-on card?

I still suspect the trace may have suffered corrosion which is mimicking the process you identified... fingers crossed I'm wrong lol.
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Old 17 January 2019, 11:26   #11
simon_m74
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All sorted!

I put Diagroms in to do tests, and the memory test passed fine on both chip & fast.

So I put the roms back in - and it works... So must of been a bad connection on the roms ?


Thanks all for suggestions and help though!

Now its working... I will start work on Lesta_smsc A500+
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Old 17 January 2019, 11:36   #12
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Well done! I was going to suggest Diagrom as I only just came across in yesterday on reading online!

May have been some dirt or something that made it not work although now I know why they say take out chips and reinsert lol.

Yay! I hope the challenge of my A500 plus is not as difficult as your A3000!
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