Purchased a board with no sound reported
Fired it up but my switcher kept power cycling. Uh oh! That means something is shorting the power!
Metered across all the power points on the finger board (+5, -5, and +12). +12 was measuring 3 ohms which is way too low! Checked the schematics and the +12 only goes to a couple caps and the audio amp. Oh look! One of the caps is missing. Lifted one leg on the other cap and still have a short so it must be the audio amp. Replaced the audio amp and both caps (the one still on the board was bulging in the bottom) and we have sound!
But what is this? The colors look off. Your plane looks all pink and the white text looks pink. Light color is made up of RGB so white being pink means either the red is over-driving or the GB are weak. Looked over the schematics and found the color output signals are generated by some color PROMs connected to resistor ladders. Measured the resistors and they were all within tolerance. Pulled out my logic probe and found that pin 2 on the color PROM @ B4 was stuck low. Pulled the PROM, programmed a new one, and everything was right with the world again, at least in Time Pilot.
Fired it up but my switcher kept power cycling. Uh oh! That means something is shorting the power!
Metered across all the power points on the finger board (+5, -5, and +12). +12 was measuring 3 ohms which is way too low! Checked the schematics and the +12 only goes to a couple caps and the audio amp. Oh look! One of the caps is missing. Lifted one leg on the other cap and still have a short so it must be the audio amp. Replaced the audio amp and both caps (the one still on the board was bulging in the bottom) and we have sound!
But what is this? The colors look off. Your plane looks all pink and the white text looks pink. Light color is made up of RGB so white being pink means either the red is over-driving or the GB are weak. Looked over the schematics and found the color output signals are generated by some color PROMs connected to resistor ladders. Measured the resistors and they were all within tolerance. Pulled out my logic probe and found that pin 2 on the color PROM @ B4 was stuck low. Pulled the PROM, programmed a new one, and everything was right with the world again, at least in Time Pilot.
