A4000 Chip RAM question

[swanng]

Greetings All-

I have an A4000 (Rev B Mobo) that is registering 1Meg Chip RAM when I have a 2Meg SIMM (70nS) in the Chip RAM slot, and I don't know why. All the jumpers on the mobo appear to be in the correct positions to allow 2Meg chip, and when I insert the exact same RAM in my other A4000 (with the same exact jumper settings on the mobo) chip RAM slot, it registers 2Meg. There was one additional problem on the Rev B motherboard from the factory that I rectified. Apparently, someone at the Commodore factory placed a sticker on the bottom of the motherboard that prevented a couple pins on the outside RAM bank from being wave soldered, and as such, when Fast RAM was fully populated, it would only recognize 12 Meg instead of 16Meg. So I fixed that problem, but still have the Chip RAM problem. Could they have been related? What should I check? Any advice would be welcomed...
Thanks!

[Bonami]

Hi Swanng, sorry i'm not experienced enough to offer any help to your Chip ram problem - it's puzzling indeed. Instead i thank you for the info regarding the Fast ram bank problem - which is exactly the problem i've had with my A4000 with rev.B mobo. When i got it the battery had just started to leak and caused some minor corrosion, hence i thought that was the reason for the failure of bank#4. (all banks were unpopulated when i got the A4k; the battery had since been removed)
Anyway, i hope to have some time to probe the bottom of the mobo later. Could you kindly elaborate how you fixed the problem please? Just get a solder gun and patch up the missing bit?
TIA. Regards, bonami.

[swanng]

Hi, Bonami-

There were two solder pads on the motherboard for the 72 pin SIMM socket on the outside bank (closest to the edge of the motherboard) that were not soldered at all. The two pads were occluded by a QA sticker which I believe prevented the pads from being wave soldered. All I did was remove the sticker, recite some obscenities directed at the Commodore QA department, and solder the two pins on the socket to the solder pads on the motherboard. That fixed the problem for me. Verify that nothing on your motherboard prevented ALL the SIMM socket pins from being soldered to their respective solder pads.

G

[Zac67]

When I upgraded my 3000 from 8 to 12 Megs I noticed many weird memory related problems. Lots of RAM tests and some research later I took out the board to find a socket with 2 address lines completely unsoldered...

I would check continuity from the SIMM socket to Alice (through U212) - probably one of the RAS/CAS lines is faulty. Are the 8/2 MB chip jumpers in the 2 MB position?

[Flashlab]

For the Amiga to recognize a 2Mb simm in the ChipRam slot it has to be a doublesided simm. You can use 4 or 8 Mb simms for this as well. As long as it's double sided it will see them as 2 Mb.

[TjLaZer]

Well he is not having a "right simm" issue.  He is clearly having a hardware issue with that MB.  Bad connection to the SIMM slot?

[swanng]

Thanks to all who have replied so far. The chip RAM jumper is set to 2Meg. The SIMM size jumper is set to 1Meg SIMM, not 256K. I have a 4Meg SIMM in the Chip RAM slot, and the machine is reporting only 1Meg chip RAM. It definitely could be a bad connection from the socket to the motherboard, so I will have to check each one. That's on my to do list, but don't want to tackle that just yet until I run out of easier (more convenient) solutions and possible problem areas to check.

G

[zipper]

I think 4 MB simms do report as 1 MB; 8 MB show as 2 MB.

[boing4000]

you can use a (single sided, 2 chips) 4MB ps/2 simm and set the two jumpers to "8M".
then you will have 2MB chip ram (the other 2MB of the simm are unavailable).
its working fine since many years in my A4000D

[swanng]

Thanks to all who responded. Ultimately, after quite a bit of testing, I found that the 2 Meg double sided SIMM I was using for the chip RAM is making an intermittent connection to the Chip RAM SIMM socket on the MOBO. Under normal circumstances, the A4000 would not boot and a flashing yellow screen would appear on my Commodore 1960 monitor. When I actually pushed down on the chip RAM SIMM with my fingers while the A4000 booted, it would boot fine and indicate 2Meg (actually a bit less after Workbench was up and running) chip RAM. Just to be on the safe side, I replaced the SIMM socket with a new one (not a job for the inexperienced) and tried again. Same thing happened, so potential problems with the MOBO or SIMM socket were dismissed. I'm waiting on a new 2Meg SIMM, but have tried the one in my other A4000 and it works fine. So, problem solved, and on to other things.