7A42

Manuals – Specifications – Links – Pictures

The Tektronix 7A42 is a four-channel 350 MHz plug-in for 7000-series scopes. It is a double-wide plug-in, with signal outputs and mainframe readout only using the left slot.

It was specifically designed for logic signals (TTL, ECL, CMOS) and supports triggering based on Boolean conditions of the four inputs. A fifth trace, "Trigger View", displays the trigger function output or external clock input.

There are two sets of conditions, A and B, that can be individually selected or paired in an "A then B" mode called nested triggering, where the occurrence of condition A arms the trigger and condition B causes the trigger to be generated. The trigger can be qualified by an external clock. A trigger filter control, variable from 0-300 ns, allows events shorter than the selected length to be suppressed. A TTL-level "reset" input will inhibit the trigger if active.

Selected by an internal jumper, either the trigger signal, or the "A then B" interval, is available on a front-panel trigger output. This can e.g. be routed to a counter for time measurement or event counting.

The input V/Div setting can only be seen in the mainframe's readout. There is a jumper to allow the readout to work in a 7854 mainframe. The trigger level is set digitally and shown on a 7-segment display.

Tektronix recommended the P6131, 300 MHz, 10 MΩ ×10 probe, and the P6230, 1.5 GHz, 450/50 Ω ×10, variable-offset probe for ECL circuits.

The 067-1155-99 calibration fixture is specific to the 7A42.

Key Specifications

Bandwidth	350 MHz
Deflection	0.1 / 0.2 / 0.5 V/Div (TTL mode) 20 / 50 / 100 mV/Div (ECL mode) each direct or through 10:1 probe always DC coupled
Input impedance	1 MΩ // 15 pF or 50 Ω
Max. input voltage	at 1 MΩ: 25 V (DC+peak AC) below 36 MHz, down to 3 VAC at 300 MHz at 50 Ω: 5 VRMS during any 1 ms interval
Trigger level	−1.27 to +1.28 V (TTL mode) in 10 mV steps −254 mV to +256 mV (ECL mode) in 2 mV steps (or ×10)
Hysteresis	40 mV (TTL), 8 mV (ECL) (or ×10)
Features	NiCd battery to preserve front-panel control status
Weight	2.8 kg / 6.2 lb

Links

Documents Referencing 7A42

Document	Class	Title	Authors	Year	Links
42W-5588.pdf	Application Note	Advanced Triggering Techniques	Roger Ensrud	1984	7A42 • 7D11 • 7D15

See also

• 067-1155-99
• A6701
• 821

Internals

The 7A42's functions are controlled by an Intel 8085A microprocessor, with code in three 2764 EPROMs (a fourth ROM socket is unused). The front-panel pushbuttons are handled by an Intel 8279 keyboard controller.

Each of the four 119-1517-00 input attenuator modules contains five 148-0145-00 miniature bi-stable relay actuators. These have four long pins plugging in to the base board, driving two solenoids that move aa yoke which is held in the last active position by a permanent magnet. The yoke moves a pair of contact springs that directly short corresponding pads on the thick-film ceramic substrate. The relay coils are wired in a 4×5 matrix.

The 7A42 contains its own switch mode PSU, based on an SG3524 controller, that generates +5 V, −2 V and −5 V from the mainframe's ±50 V rails.

There is a NiCd backup battery that allows the unit to retain its last configuration.

A 555 timer implements a 15 ms "real-time clock" and watchdog reset, another drives a beeper.

An internal jumper enables partial compatibility with a 7854 mainframe in storage mode (displaying any single channel, 1+2 in ALT, or 3+4 in ALT only). There are no restrictions with the 7854 in analog mode.

Pictures

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  display - four signal traces plus trigger view

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  7A42 rear view

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  7A42 top view

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  Schematic cartoon: Bus

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  Schematic cartoon: Chirp

Internal

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  amplifier board (one attenuator cover removed)

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  amplifier board front - attenuators, amplifiers, channel switches

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  amplifier board rear - channel switches, two 15 ns delay lines

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  attenuator, cover removed

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  attenuator cover

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  attenuator, top

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  attenuator, one relay actuator removed

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  attenuator, all relay actuators removed

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  attenuator, all relay actuators removed

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  microprocessor board

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  memory backup battery on microprocessor board replaced with LiIon

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  internal switch mode PSU for digital logic supplies

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Components

Some Parts Used in the 7A42

Part	Part Number(s)	Class	Description	Used in
148-0145-00	148-0145-00	Discrete component	miniature bi-stable relay actuator	7A42 • 119-1517-00
155-0038-01	155-0038-00 • 155-0038-01	Monolithic integrated circuit	5-bit current source D/A converter	7A42 • 7D13 • 7D14 • 7M13 • T4005
155-0078-00	155-0078-xx • 155-0273-00 • 155-0274-00	Monolithic integrated circuit	broadband amplifier	464 • 465 • 466 • 468 • 475 • 475A • 475M • 485 • 7834 • 7844 • 7854 • 7904 • R7903 • R7912 • 7912AD • 7912HB • 7104 • 7A16A • 7A16P • 7A24 • 7A26 • 7A42 • 067-0587-01 • 067-0680-00 • AM503 • PG502 • PG508 • DC510 • DC5010 • FG5010
155-0236-00	155-0236-00	Hybrid integrated circuit	channel switch	2445 • 2465 • 7A42
ICM7218	156-1621-00 • 156-1622-00	Monolithic integrated circuit	8-digit, 7-segment LED driver	7A42
Intel 8085	156-1088-00	Monolithic integrated circuit	8-bit microprocessor	308 • 468 • 4025 • 7A42 • 7D02 • AFG5101 • AFG5102