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!

[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

[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

[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.