User manual

Vetta and FBX Service Hints Page 2 of 2
If the DC bias voltage at the input pin 25, 24, 4, or 5 of the guitar input ADC U19 is
significantly off from its nominal value of 2.5V (less than 1.8V or more than 3.2V), the
part is probably bad. The same is true for Pin 22,23, 20 or 21 of the DAC U20 and U21,
and for pin 17,16,20,19,23,24,26, or 25 of the CODEC U16.
When troubleshooting the amp PCB by itself, you can power just the +/-15V rails and
check almost the entire audio path. Once that is checked then bring up the main rails and
check to see if the proper bias rails are all correct. This process allows for easier
troubleshooting before applying the high voltage rails.
If the software locks up when changing amp models, either the battery is not working or
dead, or the Model Defaults are bad. Model Defaults are loaded via MIDI SysEx from
the Save pages, and can be loaded from a working amp or from a MIDI SysEx computer
program.