My new-to-me NEC 8201 is showing weird LCD behavior First, the contrast dial does nothing.
Second, the screen "pulses" a little bit. So, I took it apart and found that: *. The contrast pot is fine *. VDD (+5V) and VEE (-5V) are correct when measured on the LCD connector *. According to the schematic, R10 (100K) is supposed to go between VEE and the pot. The connection to the pot is there, but on the other side of R10 it measures +4.3V. (positive, not negative) *. Similarly, according to the schematic R77 (10k) is supposed to go between VDD and the other side of the pot. The connection to the pot is there, but on the other side of R77 the voltage is also around +4.3V *. The voltage at VR1 (the contrast voltage) kind of oscillates between +4.1 and +4.3V, regardless of the setting of the pot. This explains the "pulsing" I was seeing on the screen. The only things I could think of are: 1. A broken trace (or two?). I couldn't find any broken traces but also couldn't find the connections between R10 and VEE or R77 and VDD as shown in the schematic. I may have not been testing correctly, since there *is* a voltage on each of them with power on.... 2. Failure of Q2, the transistor between the pot and VR1. So, I removed it, but it tested OK. So... thoughts/suggestions?
