7A18: Difference between revisions
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==Repair issues== | ==Repair issues== | ||
===Attenuator solder joints=== | |||
The pins of the attenuator modules are connected to conductive traces on the ceramic substrate inside by low-temperature soldering, which can go bad. | The pins of the attenuator modules are connected to conductive traces on the ceramic substrate inside by low-temperature soldering, which can go bad. | ||
Re-seating the module can temporarily restore the internal contact but will usually not fix the problem permanently. | Re-seating the module can temporarily restore the internal contact but will usually not fix the problem permanently. | ||
Repair is possible by opening the click-locked lid and carefully resoldering. | Repair is possible by opening the click-locked lid and carefully resoldering. | ||
===Variable gain pots=== | |||
These pots (R237A,B and R437A,B 315-0241-00) are bonded together - looking at a few 7A18s, I see that the design was changed at least once. | |||
==Pictures== | ==Pictures== | ||
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7A18 and 7A18N from 070-1126-01.png | 7A18 and 7A18N from service manual 070-1126-01 | 7A18 and 7A18N from 070-1126-01.png | 7A18 and 7A18N from service manual 070-1126-01 | ||
Tek 7a18n.jpeg | 7A18N with "Identify" Kurt to check? | Tek 7a18n.jpeg | 7A18N with "Identify" Kurt to check? | ||
7A18N front.jpg | 7A18N Front | |||
7A18N RHS.jpg | 7A18N RHS switch cover removed | |||
7A18N LHS.jpg | 7A18N LHS switch cover removed | |||
</gallery> | </gallery> | ||
===Development Prototypes=== | ===Development Prototypes=== | ||
Revision as of 04:09, 11 August 2023
The Tektronix 7A18 is a general-purpose 75 MHz dual-trace vertical plug-in for 7000-series scopes. Model 7A18N is identical except it omits the readout circuits.
Option 06 (first offered in 1975 catalog) adds offset voltage controls giving ±200 Div offset range. This option replaces the IDENTIFY buttons with DC offset controls and adds a fourth "DC offset" position to the input coupling switch.
The 200 MHz 7A26 and 400 MHz 7A24 share the same front panel layout and operation.
The 7A18 uses a discrete front-end followed by M36 channel switch ICs for the vertical and trigger signals.
Key Specifications
| Input impedance | 1 MΩ // 20 pF |
|---|---|
| Deflection | 5 mV/div to 5 V/div in 1–2–5 sequence, 2% |
| Bandwidth | 0 – 75 MHz (DC), 10 Hz – 75 MHz (AC) |
| Noise | < 300 μV in 5 mV/Div |
| Option 06 offset range | ±200 Div equiv. from ±1 V in 5 mV/Div range up to ±200 V in 1 V/Div range (above that limited by maximum input voltage) |
| Features |
|
| Weight | 1.4 kg |
Links
- Tektronix 7A18 II Repair and Alignment (With a Deeper Look at the High Frequency Compensation) @ Zenwizard Studios YouTube
- Tektronix 7A18 Repair and Function Generator Alignment @ Zenwizard Studios YouTube
Prices
| Year | 1971 | 1976 | 1980 | 1984 | 1990 |
|---|---|---|---|---|---|
| Catalog price | $535 | $615 | $915 | $1,250 | $1,790 |
| 2018 value | $3,300 | $2,700 | $2,770 | $3,000 | $3,420 |
Repair issues
Attenuator solder joints
The pins of the attenuator modules are connected to conductive traces on the ceramic substrate inside by low-temperature soldering, which can go bad. Re-seating the module can temporarily restore the internal contact but will usually not fix the problem permanently. Repair is possible by opening the click-locked lid and carefully resoldering.
Variable gain pots
These pots (R237A,B and R437A,B 315-0241-00) are bonded together - looking at a few 7A18s, I see that the design was changed at least once.
Pictures
-
7A18 Front
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7A18 attenuator opened. One of the attenuation R/C modules has been unplugged to reveal the switch contacts.
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7A18 attenuator, bottom (switch) side
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A 7603 with two 7A18s
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7A18 in 7613 mainframe
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7A18 and 7A18N from service manual 070-1126-01
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7A18N with "Identify" Kurt to check?
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7A18N Front
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7A18N RHS switch cover removed
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7A18N LHS switch cover removed
Development Prototypes
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First prototype of 7A18
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First prototype of 7A18
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Second prototype of 7A18
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Second prototype of 7A18
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Third prototype of 7A18
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Third prototype of 7A18
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Third prototype of 7A18
7A18A
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7A18A Front
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7A18A left side. The step attenuators can be seen on the left, the amplifier board on the right.
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7A18A right side. The circuit boards on top carry the readout circuitry.
Option 06
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7A18A Opt.06 Front. AC/GND/DC switches have an extra rightmost "DC Offset" position enabling the offset controls.
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7A18A Opt.06 left side (rear). Note the two blue 10T-potentiometers for offset voltage adjustment.
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7A18A Opt.06 - offset controls take the place of the Identify buttons on the standard model.
Components
Custom ICs used in the 7A18
| Page | Model | Part nos | Description | Designers | Used in |
|---|---|---|---|---|---|
| 155-0022-00 | M036 | 155-0022-00 • 155-0022-01 | analog multiplexer | Gene Andrews | 147 • 148 • 149 • 335 • 468 • 1430 • 1441 • 1461 • 1900 • 1910 • 2220 • 2221 • 2230 • 5223 • 5403 • 5440 • 5441 • 5443 • 5444 • 5A38 • 7313 • 7403N • 7503 • 7504 • 7514 • 7603 • AN/USM-281C • 7613 • 7623 • 7623A • 7633 • 7704 • R7704 • 7704A • 7834 • 7844 • 7854 • R7912 • 7912AD • 7912HB • 7904 • R7903 • 7904A • 7934 • 7A12 • 7A18 • 7A18A • 7A18N • 7B52 • 7B53N • 7D10 • 7D11 • 7D12 • NT-7000 • P7001 |
Custom ICs used in the 7A18A
| Page | Model | Part nos | Description | Designers | Used in |
|---|---|---|---|---|---|
| 155-0022-00 | M036 | 155-0022-00 • 155-0022-01 | analog multiplexer | Gene Andrews | 147 • 148 • 149 • 335 • 468 • 1430 • 1441 • 1461 • 1900 • 1910 • 2220 • 2221 • 2230 • 5223 • 5403 • 5440 • 5441 • 5443 • 5444 • 5A38 • 7313 • 7403N • 7503 • 7504 • 7514 • 7603 • AN/USM-281C • 7613 • 7623 • 7623A • 7633 • 7704 • R7704 • 7704A • 7834 • 7844 • 7854 • R7912 • 7912AD • 7912HB • 7904 • R7903 • 7904A • 7934 • 7A12 • 7A18 • 7A18A • 7A18N • 7B52 • 7B53N • 7D10 • 7D11 • 7D12 • NT-7000 • P7001 |