A2000 Rev 6.2 only showing 512k of RAM

[SEgamer]

This is a continuation of this thread:
http://www.amiga.org/forums/showthread.php?t=61748

In short, I only get 512k of chip RAM to show up in SysInfo v3.18 and in the  Workbench configuration it only sees 512k chip RAM too. Neither one  shows signs of even seeing the other 512k which is causing the video toaster programs to yell at me about the chip RAM.

Here are the specs again:
GVP 68030 accelerator card @ 33 MHz
12 MB expanded RAM (4MB on the card, 2 x 4MB SIMM cards)
1 MB onboard RAM (8 x 256x4 chips)
SCSI interface w/ Quantum Fireball 2GB HDD (surprisingly most files are still there)
Motherboard Rev. 6.2
Kickstart 3.1
No keyboard (working on a deal at the moment), but did come with a mouse

Agnus is 8372A (1MB)
J101 originally set to pins 2 and 3
J102 originally soldered together (some people have had luck changing this one)
J500 originally open

No matter what jumper configuration I do with J101, J500, and J102 it still won't show the full 1 MB. The only time something different happened was when J500 was closed and J101 was set to pins 1 and 2 - this caused the screen to roll and the computer didn't do anything. I also changed from Kickstart 2.04 to 3.1, still not working right. Tried with and without the video toaster board and accelerator board without success.

I've checked the board for battery corrosion. There was some on one RAM chip, but I cleaned the pins, re-heated them with a soldering iron, checked the continuity of all onboard RAM chips, and used my dad's Huntron Tracker for a quick look to see if any of the chips have gone bad (all showed same characteristics, so should be good). I've also cleaned/re-seated every socketed chip, but still get only 512k RAM.

The only thing I can think of is that part of Agnus has kicked the bucket, since it should see 1MB regardless of the jumper configurations (correct?) since all the jumpers do is split or merge that 1MB into chip/fast ram.

I could just live with it as is, but knowing that something ain't right with it will bug me!

[shaf]

The J102 Jumper is if you are using the Later Agnus 8375 and controls the Video Mode Switch between NTSC and PAL. The 8372A Chip might be defective, try to use a PLCC remover to check the alignment of Pins in the Socket and reseat the Fat Agnus Chip.

[amiga-penn-wchester]

I have an A2000 + video toaster + C=68030 accel, which originally had normal agnus.   When I added a 1MB agnus from an A500, I had still 512k chip. I had to change a jumper and cut a solder bridge.  Might check into how the accel is autoconfiguring the memory, check the amiga hardware database for jumper settings on your particular accel, or - yes - try another / reseat 1mb Agnus if you can.

[SEgamer]

I'm almost certain it's not the accel board because the problem still occurs without it installed. I checked the pins and re-seated the Agnus when I re-seated the others, so it should be making contact. I'll clean the PLCC connector pins and check the traces going to the chip. It's just weird that the Agnus is acting like an older one that could only go up to 512k RAM.

[amiga-penn-wchester]

Ah, missed that part above about removing the accelerator. The only things I can think of would be 1) agnus tight in the socket, 2) replace if you can.  Have you looked at a CLI and do 'avail' to see what it reports?  In other words is the extra 512 not addressed by agnus showing up as "other memory" (fast+slow) = 12.5meg, or is the extra 512k just "not there"

[SEgamer]

Don't have a keyboard unfortunately so I can't use CLI yet, probably won't be until late next week until I get one. I did use the configuration program in Workbench, and it reported only 512k chip ram and no fast ram. With the accel board in, it reported 512k chip ram and 12MB fast ram. With the accel board installed, the Workbench 2.05  title bar reports around 450k graphics mem, and around 12.3 MB of other mem. I'm assuming graphics mem should still be near 1 MB. I thought it was reporting the full amount before, but I forgot that 12 megs is really 12582912 bytes.

I believe everything in the A2000 was originally used/working with it. The GVP device files and Video Toaster files were already on the hard drive when I got it, so something somewhere along the line has failed.

[Zac67]

Actually, all PLCC Agnus types can control 1 MB RAM. However, the older OCS types cannot make it usable as chipmem due to register restrictions - setting them up that way will crash the system. So C= invented the remapping from $08 to $C0 (J101 on 2-3) to render it useless as chipmem; Gary requires the _EXRAM signal to activate the RAM up there (J500 closed). J101 on 1-2 will map the 2nd 512KB to $08 as chipmem and requires J500 open and a compatible Agnus. (J500 open will NEVER deactivate the RTC, this is definitely nonsense on BBoAH).

J101 on 2-3 will remap the RAM to $C0 for Agnus but J500 open deactivates it with Gary - so only 512 KB visible is what is set up. Move J101 to 1-2 with an ECS Agnus or close J500 with an OCS Agnus. Both J101 on 1-2 and J500 closed will activate the 2nd 512K on BOTH locations - which will crash the system, obviously.

J102 is NTSC (closed) vs PAL (open) with a switchable Agnus. There's no connection to the RAM modes whatsoever.

If the RAM isn't accepted (added to system on boot) I suspect a bad contact or a bad RAM chip in the 2nd bank. Run a RAM tester on absolute addresses $080000 - $FFFFFF.

If you're not sure that it's been working with this exact Agnus at all, it is possible that it's a 2 MB type which won't work in a 2000 that way. You need to check with the exact part no.

[SEgamer]

Retried all of the jumper configurations and checked the traces to the ram and chips connected to the ram chips which were all fine. I'll try a ram tester this weekend, but I think Agnus is the problem.

[FuzzyNormal]

I have the same issue.  Reviving thread to see if this user got it resolved?  My understanding bopping around the internet is that it's typically chip u103, 104, 105, or 106 failure?

My story:  Amiga 2500. Sat unused for 2 decades. Booted it two years ago and was able to launch my Video Toaster. Said, "cool," then put it back in the closet for 30 months. Well, finally decided to mess around with it again.

Pulled it, cleaned it, put it back together.

The quantum drive began to fail. My Chip RAM wasn't showing 1MB like it's supposed to. Toaster won't launch.

Well, hell.

Guess I broke something. Now what? I ordered a AmigaKit floppy disk from eBay, but that's not getting here 'til mid July.

Advice appreciated. Thank you!