A bad RAM upgrade shows itself fast.

Pretty much right away.

Boot failures are the most common sign. The machine either won’t power on at all, or it spins up and does nothing. No POST, no beeps, no display. That often means a cold solder joint or a bridged connection.

Memory errors are the second sign. If it boots but crashes randomly, throws kernel panics, or fails memory tests, the solder job is brittle. Intermittent errors are worse — they mean a connection that works when warm or in a certain position, then breaks.

Physical signs matter too: any visible solder bridges, dull or grainy joints (cold solder), or lifted pads mean the job needs a redo. If you used too much heat, you might have damaged the pad or the chip itself.

Honestly, if you’re asking this question, you probably shouldn’t be doing a soldered RAM upgrade. It’s one of the hardest soldering jobs in consumer electronics. Pay a pro.