NFL Blitz 99 Repair Logs
Symptom: Dead Short
Replaced 2 shorted tantalum capacitors on the -5v line and tested.
Symptom: Will not work in Standard Res mode
Tested the DIP switches and found that U8 Switch 2 was stuck open. Replaced the surface mount DIP switch with one from a parts board and tested.
Symptom: Buzzing sounds from speakers, won't enter test mode
Board was VERY dirty. Cleaned board and replaced both sets of DIP switches. Audio issue was very odd. The hard drive, video, and any other operation could be heard through the speakers. The noise could be seen as ripple on the +5, -5, and +12v lines and No audio from the game was present. Pulled the D/A converter with no change. Pulled the audio op-amp and noise disappeared. Replaced the op-amp and reinstalled the D/A converter then tested.
The bad op-amp was overdriving the audio output IC and causing the loud noise. The overdriving also caused large current pull from the power supply which showed as ripple on the outputs and as noise through the speakers.