
Service | Model 8904A |
A3 OUTPUT ASSEMBLY (Service Sheets 1 through 4)
General
The A3 Output Assembly converts the digitally encoded waveform from the digital waveform synthesis integrated circuit (DWSIC) on the A2 Digital Assembly to a precise and useable analog signal. Instruments with Option 002 have a second Output Assembly (designated A10) which is identical to A3. For troubleshooting purposes the two Output Assemblies can be interchanged or compared
0the
0a
0clean up filters
0amplifiers and attenuators
0reverse power protection
Digital-to-Analog Converter (Service Sheet 1)
IC U6 is a 12 bit
The output of the DAC is converted to a voltage by the series combination of resistors R210, R224, and R221. R224 (DAC Level) is adjusted to give the correct waveform amplitude. Connector 54 is a convenient point for testing the DAC when jumper 5201 is moved to connect point 2 to point 3.
Track-and-Hold Circuit (Service Sheet 1)
After data is placed on the input of the DAC, the DAC requires 300 ns (that is,
The
0Sampler Drive
0Sampler Switch
0Sampler Amplifier
Sampler Drive
The Sampler Drive must provide sufficientcurrent through transformer T1 to turn on hard the sampler diodes (U201A, B, C, and F) in the Sampler Switch. When the sampler diodes are on, the voltage at the DAC output transfers to capacitor C219 at the input of the Sampler Amplifier. Operation of the Sampler Drive is most easily seen by referring to the simplified schematic of Figure