View source for 7A42

{{Plugin Sidebar
|manufacturer=Tektronix
|series=7000-series scopes
|type=7A42
|summary=350 MHz four-channel logic triggered amplifier
|image=Tektronix 7A42 front.jpg
|caption=7A42 front view
|introduced=1984
|discontinued=1990
|manuals=
* [[Media:070-4285-00.pdf|7A42 Operator Manual]] (OCR)
* 7A42 Service Manual
** [[Media:070-4286-00.pdf|070-4286-00 Volume 1]] (OCR)
** [[Media:070-4654-00.pdf|070-4654-00 Volume 2, Signature Analysis Tables]] (OCR)
<small>
'''ROM images'''
* [[Media:160-1959-00.bin|160-1959-00.bin A8U145]]
* [[Media:160-1960-00.bin|160-1960-00.bin A8U245]]
* [[Media:160-1961-00.bin|160-1961-00.bin A8U340]]
</small>
}}
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.

{{BeginSpecs}}
{{Spec | Bandwidth | 350 MHz }}
{{Spec | 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 }}
{{Spec | Input impedance | 1 MΩ // 15 pF or 50 Ω}}
{{Spec | Max. input voltage |
* at 1 MΩ: 25 V (DC+peak AC) below 36 MHz, down to 3 V<sub>AC</sub> at 300 MHz
* at 50 Ω: 5 V<sub>RMS</sub> during any 1 ms interval}}
{{Spec | 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)}}
{{Spec | Hysteresis | 40 mV (TTL), 8 mV (ECL) (or ×10)}}
{{Spec | Features |
* NiCd battery to preserve front-panel control status}}
{{Spec | Weight | 2.8 kg / 6.2 lb}}
{{EndSpecs}}

==Links==
{{Documents|Link=7A42}}

==See also==
* [[067-1155-99]]
* [[A6701]]
* [[821]]

==Internals==
The 7A42's functions are controlled by an [[Intel 8085]]A 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|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 [[7A42/Repairs|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==

<gallery>
Tektronix 7A42 front.jpg
Tek 7a42.jpg
Tek 7a42 1.jpg
Tek 7a42 2.jpg
Tek 7a42 fr1.jpg
Tek 7a42 fr2.jpg
Tek 7a42 fr3.jpg
Tek 7a42 fr4.jpg | display - four signal traces plus trigger view
Tek 7a42 fr5.jpg
Tek 7a42 fr6.jpg | 7A42 rear view
Tek 7a42 fr7.jpg | 7A42 top view
Tek-7A42-Bus.jpg                       | Schematic cartoon: Bus
Tek-7A42-Chirp.jpg                     | Schematic cartoon: Chirp
</gallery>
'''Internal'''
<gallery>
7A42 amplifier board.jpg  | amplifier board (one attenuator cover removed)
Tek 7a42 fr11.jpg         | amplifier board front - attenuators, amplifiers, channel switches 
Tek 7a42 fr12.jpg         | amplifier board rear - channel switches, two 15 ns delay lines
7A42 attenuator 1.jpg     | attenuator, cover removed
7A42 attenuator cover.jpg | attenuator cover
7A42 attenuator 2.jpg     | attenuator, top
7A42 attenuator 3.jpg     | attenuator, one relay actuator removed
7A42 attenuator 4.jpg     | attenuator, all relay actuators removed
7A42 attenuator 5.jpg     | attenuator, all relay actuators removed
Tek 7a42 fr10.jpg         | microprocessor board 
Tek 7a42 fr8.jpg          | memory backup battery on microprocessor board replaced with LiIon
Tek 7a42 fr9.jpg          | internal switch mode PSU for digital logic supplies
Tek 7a42 13.jpg
Tek 7a42 14.jpg
Tek 7a42 15.jpg
</gallery>

==Components==
{{Parts|7A42}}

[[Category:7000 series vertical plugins]]