Looking at the schematic:
- Vio/Yel = 50V, PPB J7, Pin 3
- Brn/Blk = Return, PPB J8, Pin 4
- 1N4001 across the leads
1. You noted if you bring return to ground, coil fires. Removing J8 and connecting Pin 4 in the connector to ground should produce the same result. If YES, then you have ruled out a break in the return wire.
2. Next, check the diode that sits across the coil's leads. Inspect the solder connection - if broken or funky, reflow them.
3. Next, with power off and DMM in diode mode, you want to measure voltage drop across the diode's leads (~500mV is correct range), with black lead on the banded end of the diode, red on non-banded end. If short or open, simply replace the diode, keeping the correct orientation.
1. Appears you are getting voltage to the coil via J7, Pin 3, though 78V seems high - this should be closer to 50V, per the schematic. I just checked my OEM PPB - I too read 75V on J7, Pins 1, 2, & 3. Let's rule that out.
2. Look at J8 next:
- Try the simplest thing first - reconnect/re-seat J8 and try to fire the raptor coil.
- Next, look for bad/cold solder joints on the backside of the PPB, under J8, specifically on Pins 3 & 4. If you see any oddities here, I would not repair, rather make a call to Rottendog or the distributor where you purchased to get replaced.
- Next, check Diode, D18 - with power off and DMM in diode mode. You want to measure voltage drop across the leads (~500mV is correct range), with black lead on the banded end of the diode, red on non-banded end (I read 539mV on D18). This is in circuit, so not perfect. You don't want to see a short or open here.
- Transistor Q4, (TIP36C) - look at the solder connections on this device's 3 leads. If any oddities here, I'd also look to get the board replaced vs repaired. Note: I just replaced the TIP36C and Diode on my flipper board - the second time this has been replaced. I'm not sure how to diagnose transistor issues in-circuit, so looking at surrounding evidence might be the best bet: burnt pins, burnt casing, shorted adjacent diode, open resistor, etc.
I'm out on the digital stuff. This is when I'd call a technician.
Hope that helps.