DELL flash code at startup
After changing SDRAM memory to solve the BSOD problem, the DELL Latitude D610 powers on with a caps lock light flashing like this - the screen is black, nothing happens;
A quick look on the Internet and the DELL support side indicates the flashing caps lock light is the result of a SDRAM memory fault. It flashes 10 times, after which all led lights above the keyboard go off.
Swapping DELL SDRAM memory
A total of 2 Gb of SDRAM memory was seated underneath the keyboard and at the back of the laptop. Checking and re-seating the SDRAM memory modules didn't help much. Same result.
Removing all SDRAM memory and power-on results in both the CAPS LOCK and NUM LOCK light on. No blinking - in this case just 2 static LED lights - this is normal and indicates a "no memory" installed.
Want to know why? Read about DELL POST - Power-On-Self-Test.
After reading a bit more about SDRAM memory clock speeds, a swap of both the SDRAM memory modules helped! Apparently slot A (underneath keyboard) and B (at the back) are not exactly the same for all DELL Latitude models. This might be due to timing or use of mixed memory modules brands.
If that wouldn't have helped - most likely RAM memory had to be replaced.
DELL D610 memory specifications
According to DELL specifications, the D610 requires the following SDRAM memory:
This means popular SODIMM 2GB single memory module's are NOT supported by the DELL D610 and might also cause a blinking CAPS LOCK light. However, the D610 does work with a single 2 Gb PC2-6400 CL5 SODIMM memory module from KINGSTON. (Partnumber: KVR800D2S5/2G)
On top of that, the 2GB KINGSTON memory module even works in slot DIMM-B, which is underneath the D610. However, 512Mb was still seated in slot DIMM-A. With 2,5 Gb available, still the D610 reports 2Gb of memory. This is according to it's specifications.
If there's only 1 memory module, it should be seated in position DIMM-A (Latitude D610). This is under the keyboard! NOT at the easily removable hatch underneath the laptop which is DIMM-B.
Check if single memory modules work in slot DIMM-A. If both work separately, most likely they are of incompatible specifications to work together.
DELL Power On Selft Test flash code
The flashing caps lock light is the output of the POST (Power On Self Test) when the DELL Latitude D610 is starting. The POST procedure can detect all sorts of system problems and is run by a separate micro-controller on the motherboard. After POST the BIOS startup test is executed by the CPU.
When the POST completes successfully (takes 1-2 seconds), all 3 lights above the keyboard light simultaneously for about half a second.
Next the BIOS startup test starts and can output a beep code and/or displays a message on the screen. Without a successful POST, the BIOS startup test does not commence.