All you can really do at this point is trace the button wires to the corresponding chip pin and see if they toggle the voltage there or not. Start with the working mode button to verify that it measures as expected. Then trace out the others and test.
Did I miss something on the datasheet, is having the reset line sitting high an issue?
First piece of curiosity is the buttons and how they make a connection. I measured the black dot on the backside of the buttons and they are resistive. I'm assumed they are 0ohms and connect the middle copper spoke wheel to the outer copper circle, however, that doesn't seem to be the case.
I guess the question is whether the chip is getting SCL and SDA, but trying to measure anything is way too difficult.
As for the CH453D IC, it seems the five non-working buttons that go through the diodes and resistors and connect to this IC are connected to pins 1, 23, 24, 26, and 28. Looking at the datasheet, these pins have multiple purposes - from the datasheet
CH453 periodically inserts keyboard scan during the display driver scan. During keyboard scan, the pins
DIG7~DIG0 output high level in sequence from DIG0 to DIG7, and the remaining pins output low level.
The outputs of the pins SEG7-SEG0 are disabled. When no key is pressed, SEG7-SEG0 are pulled down to
low level. When a key is pressed, for example, the key connecting DIG3 and SEG4 is pressed, SEG4 detects
high level when DIG3 outputs high level. In order to avoid error code caused by key jitter or external
interference, CH453 performs two scans. Only when the results of two keyboard scans are the same, the key
will be confirmed to be valid. If CH453 detects a valid key, the key code will be recorded, and active low
keyboard interrupt will be generated through INT# pin. At this time, the MCU can read the key code through
the serial interface. CH453 does not generate any keyboard interrupt until a new valid key is detected.
INT# is used for keyboard interrupt output and is at high level by default. INT# outputs keyboard interrupt
active at low level when CH453 detects a valid key. After the MCU is interrupted, it performs a read
operation to CH453, and CH453 recovers the INT# to high level and outputs the key code from SDA. The
MCU gets a byte of data from SDA, among which the lower 7 bits are the key code.
When the X_INT bit is 1, up to 15-bit LED Nixie tubes are supported. DIG15 pins are used for keyboard
interrupt output, whose functions are the same as the INT# pin.
Also, don't forget, the dial doesn't change the front panel numbers either; unless it's dependent on a particular button being pushed first.
Once the dial is removed, the shaft can slide out the backside. The bottom of the shaft is just copper plating that sits inside the potentiometer on the PCB. That pot (maybe it's obvious from the picture) has various copper pads. From what I can tell, the base of the pot is soldered onto the PCB with no electrical connection. There are three leads that solder onto the PCB, one is ground and the other two sit at equal voltages (I measured them but forgot the voltage). I'm assuming it's nothing more than a simple wiper and without the shaft inserted into the pot, the voltage sits in the middle of the two points.
I measured the pins at the encoder and I didn't see a waveform. I saw a 4v DC voltage, and, as I turned the knob (I stuck it in and held it in place while turning) the voltage would go to 0v periodically. Eventually I could slowly turn the knob and get it to sit at 0v or 4v, however, at no point did I see a middle voltage or a waveform.
As for the buttons, the inner spoke on all the buttons (except the 'mode' button) are common and go to pin 4 of the CH453 and one of the seven segment display pins.
5.3. Keyboard Scan
CH453 keyboard scan feature supports an 8×8 matrix 64-key keyboard. During keyboard scan, pins
DIG7~DIG0 are used for the column scan output, and SEG7~SEG0 pins have internal pull-down resistors
for the line scan input.
CH453 periodically inserts keyboard scan during the display driver scan. During keyboard scan, the pins
DIG7~DIG0 output high level in sequence from DIG0 to DIG7, and the remaining pins output low level.
The outputs of the pins SEG7-SEG0 are disabled. When no key is pressed, SEG7-SEG0 are pulled down to
low level. When a key is pressed, for example, the key connecting DIG3 and SEG4 is pressed, SEG4 detects
high level when DIG3 outputs high level.
Maybe this function of the IC got damaged because someone pushed two or more buttons simultaneously (or one got stuck and another was being pressed) and the driver couldn't handle the low impedance.
Maybe ordering them will not be so easy.
I don't see them on Digikey, Mouser, and Aliexpress appeared in a Google search but the page wasn't found.
I don't want to contradict myself, but it almost seems the display board could be fine and I need to dig into something like a reference voltage.
I found one high wattage resistor that looks like it took some heat. It seems to measure lower than the (I believe) 10ohms; I'm measuring 2.9ohms (capacitor seems to be good).
I'm not sure I understand the circuit though.
From what I can tell, the negative input on the front panel goes to the capacitor in the picture (and that pipe looking thing which I believe is a type of low ohm resistor), the other side of the capacitor to the resistor, and the other side of the resistor to ground.
The large metal pole (shunt) doesn't look like it connects to the positive input terminal, but I could be wrong.
I don't see what purpose the cap and resistor serve since the connection between the two doesn't look like it goes elsewhere (hard to tell because the components are soldered close to the board covering traces).
I wouldn't think so. But once you solve the button/knob problem, it'll be worthwhile to replace R2.
24LC541 or SN1747 (uncertain which is the part number) - EEPROM I think
I don't know the relationship between the microcontroller and the EEPROM.
Why are you uncertain of the part numbers? What is written on the ICs?
SN74HC14 has 1v on the input (pin 13) and 5v on the output (pin 12). All other gates are basically 0 with an output at 5v or vice versa. Pin 13 is the only one sitting at a point that isn't 0 or 5v. I'm confused on the datasheet because this is a Schmitt trigger inverter. I don't understand why it's showing waveforms on page 8 that shows the input and output are a high or a low (implying it's a bugger and not an inverter), and then it shows another figure with two outputs.
I don't understand at which voltage triggers the output to go opposite the input.SN74HC14 datasheet:
Maybe they change state when buttons are pushed, but I can't access the button side while trying to measure pins on the other side.You can solder small wires and have easier access this way - hot glue will hold them in place. Label for each wire would be helpful as well.
Does anyone think the M430 can be partially working?
Yup. It's entirely possible. I've seen MCUs with just a single pin gone bad.
I found a programmer for MSP430 chips, but it was over $300; clearly not worth buying.The official MSP430 programmer, the MSP-FET, is $115.