Last year I built a DR clone, and wanted reverb on both channels. When I fired it up, I only had sound when the reverb level turned up. I looked and looked, but found nothing, and put it up for a while. I got it down recently, and once again, I found nothing wrong, until I discovered the 470K ohm resister in the reverb out, was really 470 ohm! I have always prided myself on knowing the color codes, and when younger used to "help" my uncle find the values he was needing.
Even with reading glasses, I guess I'll have to start checking values with a meter!