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Sometimes the knob LEDs will be on, but the button LEDs will be off. This I find odd, because the knob LEDs get their on/off signal indicator from one of the legs of the button LEDs. So I guess that means the button LEDs aren't getting enough juice to light up, but they are getting enough juice so that the signal to activate the knob LEDs is working.

The signal only has to be slightly over 0.7V to fire up the transistor that feeds the knob LEDs, but will have to be over 2V to light the button LEDs...
Hmm come to think of it, IIRC, the LEDs may have constant 5V and switched ground, with the transistor being PNP, meaning the signal would have to be below 4.3V for the knob LEDs to light yet below 3V before the buttons lit.

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When the button LEDs are malfunctioning, if I go into the dimmer menu on the player, it does not affect the brightness of the VFD display. Only after I press on the face to make the buttons light up, does the dimmer menu actually cause the display to change brightness.


When this happens does pressing the face immediately make the dimmer change to its new setting, or does it wait until you make a subsequent change?

If the latter, this might tie in with a power/grounding problem on the PIC. The PIC controls the display brightness. button inputs, and the LEDs. A bad Vss (that's what we call 'ground' on CMOS logic chips) could result in the PIC not being able to drive the button LED output low enough to turn the button LEDs on. It could also screw up communications between the PIC and the CPU on the mainboard such that the PIC didn't correctly interpret dimmer commands.

The PIC should have a power decoupling capacitor very close by that should prevent noise issues on the power supply from interfering with the PICs operation. It is possible that there is a problem with that capacitor. The capacitor will be connected directly across Vdd and Vss. You should be able to locate it easily on the board as it should be a small chip capacitor (like an SMD resistor only less 'flat', unmarked and typically gray/pale brown/mauve in color) and it will be as near to the PIC as physically possible.

Also check the Vss connection. I'm not sure whether the display board has a separate power 'ground' for the VFD or whether the VFD and logic currents share Vss. If the former you may find that the PIC's Vss is a pcb trace. If the latter then it may well be connected to a ground layer within the pcb if the pcb is 4 layer, or a trace if it is 2 layer. ( I can't remember which it is. ) Anyway, look for a dodgy connection there.
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