The following boards are all plugged into the card rack, starting from the right end as viewed from the front. The card rack is located behind the 2nd panel from the top of the tester. There are also some test points, jacks, and BNC connectors behind this panel. The BNC connectors are for scope sync. The board names link to schematics.
- B621 COMPUTER INTERFACE - This is located behind the card rack. It is accessed through the back door, and is connected by a cable to the parallel port (LPT1) in the PC. This board contains 8 octal output registers and 3 octal input ports. These allow the PC to control all the functions of the tester and to read some data back to the PC.
- B500 - This is a dual 14-bit DAC with associated references and circuitry to control modulation for AC tests.
- B501 - This contains a track/hold, analog comparator, and 8 channel analog multiplexor, all part of the 14 bit ADC. It also contains a differential input ranging amplifier for ranges of 1.6383V and 16.383V.
- B552 - This board is a signal conditioning and ranging circuit for DC voltage and current. It is used for all IR ranges and for VZ ranges 163.83V and up. It also contains a modulation extractor circuit to output the AC component of the parameter being measured. This AC voltage goes to the next board, which ranges, rectifies, and filters it.
- B530 - This takes AC millivolts from the B478. The AC is amplified in three ranges, rectified, and filtered. The output is fed to one of the 8 ADC inputs. The B391 is used only for impedance tests such as ZZT, ZT, etc.
- B400 - This is a constant current generator for the three lowest ranges. It supplies reference currents for both constant voltage and constant current tests. It presently also contains some logical decoding of range control codes for the four ranges of the next board (which supplies the higher current ranges).
- B534 - This constant current generator supplies the forcing current for VF tests above 4mA. It supplies reference current for Reverse tests above 4mA but in this case the following board (B507) directly drives the DUT.
- B507 - A booster amplifier for voltages up to 500V and currents up to 5A. The B507 is used for all Reverse tests and for VF tests from 4mA down. Think of it as a high power co-amp, with a logical disable input. This board also contains circuitry to limit the maximum output voltage. This function is programmed with an analog voltage from DAC1, which is remembered by a sample hold circuit.
- B368 - For Polarity and Kelvin contact testing. On command this board performs the above tests and tells the CPU the results through one of the input ports.
- B502 (4) - Facing the rear of the tester. These are the four station interface drivers.