Ferranti ZN401 Test Box
| |
| Caption | Part of Ferranti's sequencer drawing, 12 October 1983: the step timing chain and the reset relay on pins 21 and 22 |
|---|---|
| Type | Automatic production tester for the ZN401 television IC |
| Designer | Ferranti |
| Manufacturer | Ferranti (several built for its own use) |
| First released | Drawings dated 28 September to 18 November 1983 |
| Latest revision | — |
| Operating voltage | +12 V and 5 V internal rails; device supply 3.9 to 6.5 V |
| Layers / PCB | — |
| Compatibility | Ferranti ZN401, the custom IC of the Sinclair TV80 pocket television |
| Features | Relay-switched device supply, line standard, sound carrier and IF level; 35 mA current limit; window comparators; true RMS sound detector; PASS and FAIL lamps |
| Model No. | — |
The Ferranti ZN401 Test Box was test equipment that Ferranti designed between September and November 1983 to test the ZN401, the custom integrated circuit in Sinclair's TV80 flat-screen pocket television. Ferranti's drawings call it the "Sinclair TV test box"; its folder in the Ferranti Archives 2026 and a covering memo call it the "ZN401 test box".[1][2]
It works in the opposite way to the Ferranti Spectrum ULA Test Box, which relied on an operator watching a TV. The ZN401 box is built from relays, TTL logic and analogue comparators. It steps the chip through test conditions numbered 0 to 10, setting its supply voltage, signal level, line standard and sound carrier for each; it checks DC levels, AGC, sound output, lock and the EHT drive pulses against fixed limits, and lights a green PASS or red FAIL lamp.[3][4]
The ZN401 and the Sinclair TV80
[edit | edit source]The test box documents only say "Sinclair TV". Outside sources identify the chip:
- The Sinclair TV80, also sold as the Flat Screen Pocket TV or FTV1, was released by Sinclair Research in September 1983. It used a flat CRT with the electron gun at the side, viewed through a Fresnel lens; about 15,000 were sold.[5] The wiki has no page on the set yet.
- The circuit diagram in the FTV1 service manual labels the set's custom IC, IC1, "ZN 401E-2". The manual's description of IC1's pins matches the pins used on Ferranti's test box drawings (see ZN401 pin functions below).[6]
- A review of the set in Modern Electronics in January 1986 calls it the first TV to put almost all its circuitry on a single chip, "designed by Sinclair Research and produced by Ferranti Limited (using its FAB2 CDI process)". The chip takes the IF from the tuner at 230 MHz, recovers the video and sound, handles 625-line systems with 6.0 or 5.5 MHz intercarrier sound as well as the 525-line system, and generates the scan waveforms for the flat CRT digitally.[7]
The test box exercised the same features: both line standards, both 625-line sound carriers, two IF signal levels, and the output that drives the set's power converter.[3][6]
Production context
[edit | edit source]A handwritten memo of 25 November 1983 from Ferranti's Applications Manager records that the IC Applications Department had been asked for engineering effort "with the aim of getting several test boxes into commission as soon as possible in order to alleviate the urgent backlog of ZN401 devices awaiting test". It sets out, "on a temporary basis", that IC Applications would take overall engineering responsibility for producing and commissioning the ZN401 test boxes until the project could pass to the IC Test Department, "hopefully" within six months. The department's duties were to supervise wiring and construction, check out and test the circuit boards, commission completed units, and carry out limited maintenance and calibration of units in service. Wiring and construction were to move to a test department as soon as possible, and routine maintenance and calibration to the Test Department, with only major repairs and modifications referred back to IC Applications.[2]
The memo is later than every dated drawing in the folder: the relay table is dated 28 September 1983, the power supply, sequencer and pass/fail drawings 12 October, the circuits for tests 3, 5, 8 and 9 2 November, and the sound and AGC circuits 18 November.[3][8][9][10] The TV80 had gone on sale in September.[5]
Construction
[edit | edit source]The drawings divide the box into separate boards and enclosures:
| Part | Drawings | Contents |
|---|---|---|
| Power supply board | TV-FER-SCH-157 (layout), TV-FER-SCH-159 (circuit) | Device supply to pin 12; relays RL5 to RL8; 35 mA current source; supply monitor |
| Measurement board | TV-FER-SCH-158 (layout), TV-FER-SCH-163 and TV-FER-SCH-164 (circuits) | Comparators for the DC, lock, AGC and sound checks; AD536A RMS converter; 74122 EHT pulse detector |
| RF attenuator and input switching | TV-FER-SCH-162 | Coaxial relays RL3 and RL4A to RL4C and a 33 dB attenuator on a copper ground plane |
| Relay drivers | TV-FER-SCH-160, TV-FER-SCH-161 | One 8-input gate and one transistor per relay, with indicator LEDs |
| Sequencer | TV-FER-SCH-165 | Step button, step timing, step counter and decoder, TEST NUMBER display; the reset relay is "on sep board" |
| Pass/fail logic | TV-FER-SCH-166 | Flag gating, fail and pass latches, red and green lamps, supply-off signal |
| Elsewhere | TV-FER-DAT-167 | RL1 (sound on or off) "in die-cast box 1"; RL9 (625 or 525 composite sync) "in die-cast box 2"; RL2 (British 6 MHz or German 5.5 MHz sound) "in Philips" |
The logic is TTL on 5 V: low-power 74L00, 74L04, 74L10 and 74L30 gates, with 7400, 7430, 74121, 74122, 74154, 74163 and 7447. The comparators are Ferranti ZN424 operational amplifiers, with ZN458 and REF25Z references; the transistors are ZTX300, ZTX450 and ZTX500; the sound detector is an Analog Devices AD536A true RMS-to-DC converter, marked "R.S." on the drawing. The power supply board and the RF relays run from +12 V.[8][9][10][11][12]
| Control | Conditions for each step | Device under test | Measurement | Result | ||||
|---|---|---|---|---|---|---|---|---|
| Front-panel step button and RESET AND SYNC button; sequencer with step counter, decoder and TEST NUMBER display | → | Relay drivers; RL1 sound on or off; RL2 6 or 5.5 MHz sound; RL3 625 or 525-line signal; RL9 625 or 525 sync; RL4A to RL4C 10 mV or attenuated; RL5 to RL7 supply voltage; RL8 current limit | → | ZN401: supply on pin 12, IF into pins 19 and 18; pins 21 and 22 joined while RESET AND SYNC is held | → | Pins 9 and 14 DC windows; pin 3 lock; pin 17 AGC; pin 11 sound (AD536A); pin 6 EHT pulses (74122); supply monitor | → | Flags sampled by the strobe; fail latch (also set by VIDEO FAIL); green PASS or red FAIL lamp; device supply switched off |
Device supply and current limit
[edit | edit source]
Four ZN458 voltage references in series, fed from +12 V through 150 Ω, form a reference. A 1K preset marked "SET 6.5" sets the device supply to 6.5 V; relays RL5, RL6 and RL7 each connect a 5K preset that pulls it down, marked "SET 4.5V", "SET 4.2V" and "SET 3.9V". Two emitter followers in cascade, a ZTX300 driving a ZTX450, pass the voltage to "Vcc PIN 12" of the ZN401, with 0.1 µF and 6K2 to ground. A ZTX300 across the reference, driven through 10K from the input "HIGH FOR SUPPLY OFF", switches the device supply off.[8]
The followers' collector line is fed from +12 V by two routes: through 62 Ω in series with the contact of relay RL8, or through a constant-current source, a ZTX500 with 27 Ω and a 50 Ω preset marked "SET 35mA" in its emitter and its base held by a ZN458. With RL8 open, only the 35 mA source feeds the device.[8] The relay table agrees: RL8 open gives a "35mA current limit" and closed "no current limit", "Relay 8 is normally closed", and RL8 is closed in every step except step 3.[3] A ZN424 comparator compares the collector line with a preset taken from the current source's ZN458. Its output drives a red LED through a ZTX300 and, through a 10K and 10K divider, gives a logic-level flag labelled HF3', written over HF6.[8] The test 3 gate on the measurement drawings has an input with the same label, HF3'.[9]
A second, identical pair of followers, with an output "B2 Vcc", is marked "N/C" (not connected).[8]
Test signal switching and attenuator
[edit | edit source]The test signal enters on two 75 Ω coaxial inputs, whose labels are cut off at the sheet edge. Relay RL3 selects one of them; the relay table gives RL3 open as "625 PAL" and closed as "525 NTSC".[12][3] Relays RL4A, RL4B and RL4C either pass the signal straight through or route it through a 33 dB, 50 Ω attenuator built from 20 dB, 10 dB and 3 dB sections. The output is terminated by a 50 Ω carbon composition resistor and coupled through 33 pF ceramic to "IF I/P PIN 19" of the ZN401, with "IF GND PIN 18" beside it. The switching is built over a copper ground plane, and RL3 and RL4A to RL4C are 50 Ω coaxial relays with 12 V coils.[12] The relay table calls the two levels "100uV i/p" (RL4 open) and "10mV i/p" (RL4 closed).[3]
The other signal relays are outside the attenuator: RL1 switches the sound on or off, RL2 chooses "British 6 MHz" (open) or "German 55 MHz" (closed; typed without the decimal point), and RL9 chooses 625 or 525-line composite sync.[3]
Sequencer and step timing
[edit | edit source]A front-panel push-button feeds a cross-coupled 74L00 and 74L10 latch that removes contact bounce. The third input of the 74L10 is an "idle" signal, high only when none of the three timing monostables is running, so a press during a step is ignored. Each press produces one step, made by three 74121 monostables in a chain:[11]
- pulse A, 1.5 ms (470 nF and 4K7), at whose start the 74163 counter advances to the next step number;
- pulse B, about 200 ms (22 µF and 15K), started by the end of A, while the relays and the measuring circuits settle;
- pulse C, 1.5 ms (470 nF and 4K7), started by the end of B and labelled "STROBE", which samples the result.
Nothing on the sheet starts the chain again by itself, so as drawn the operator presses the button once for each step. The 74163 drives a 74154 4-to-16 decoder, whose active-low outputs are the "walking zero" step lines used by the relay drivers and the pass/fail logic, and a 7447 that drives a front-panel seven-segment "TEST NUMBER" display through 180 Ω resistors.[11]
The "RESET AND SYNC BUTTON" pulls a line low that goes to the clear input of the 74163 and to a fourth 74121, whose pulse also clocks the counter, so the count returns to step 0. The same line energises a 5 V relay, "on sep board", whose contact joins pins 21 and 22 of the device under test while the button is held.[11] A RESET input on the pass/fail drawing clears both result latches.[4]
Relay drivers
[edit | edit source]Each relay has its own driver: a ZN74L30 8-input NAND gate whose inputs are the walking-zero step lines of the steps in which that relay operates, with unused inputs pulled up through 10K. Its output goes high in those steps and switches a ZTX300 and the relay coil, with an indicator LED and a flywheel diode.[13][14] The RL4A to RL4C driver takes step lines 2 and 4 to 10, and the RL3 and RL9 driver lines 6 to 10, as in the relay table. RL1, RL2, RL5 to RL8 and RL9 have 5 V coils; RL3 and RL4A to RL4C have 12 V coils.[13][14][12]
Test steps
[edit | edit source]Conditions are from Ferranti's relay table of 28 September 1983; the checks are from the measurement and pass/fail drawings of October and November 1983. Several flag numbers were revised between those drawings, so the check listed for steps 7 to 10 is the one the drawings name for that test number (see unresolved points).[3][9][10][4]
| Step | Device supply | Current limit | IF input | Standard | Sound carrier | Relays closed | Check made |
|---|---|---|---|---|---|---|---|
| 0 | 4.5 V | None | 100 µV | 625 PAL | Off | RL5, RL8 | None ("'0' & '6' go nowhere") |
| 1 | 4.5 V | None | 100 µV | 625 PAL | Off | RL5, RL8 | AGC (pin 17) below 2.5 V |
| 2 | 4.5 V | None | 10 mV | 625 PAL | Off | RL4, RL5, RL8 | Sound (pin 11) below 0.2 V |
| 3 | 6.5 V | 35 mA | 100 µV | 625 PAL | Off | None | Pin 14 within 2.7 to 3.3 V; pin 9 within 2.88 to 3.52 V; supply monitor flag |
| 4 | 6.5 V | None | 10 mV | 625 PAL | On, British 6 MHz | RL1, RL4, RL8 | Sound present |
| 5 | 6.5 V | None | 10 mV | 625 PAL | On, German 5.5 MHz | RL1, RL2, RL4, RL8 | Sound present; lock (pin 3) above 1.5 V |
| 6 | 6.5 V | None | 10 mV | 525 NTSC, 525 sync | On | RL1, RL3, RL4, RL8, RL9 | None ("'0' & '6' go nowhere") |
| 7 | 6.5 V | None | 10 mV | 525 NTSC, 525 sync | On | RL1, RL3, RL4, RL8, RL9 | Sound present |
| 8 | 4.5 V | None | 10 mV | 525 NTSC, 525 sync | Off | RL3, RL4, RL5, RL8, RL9 | AGC (pin 17) above 1.5 V; EHT pulses present (pin 6) |
| 9 | 4.4 V (4.2 V on the power supply drawing) | None | 10 mV | 525 NTSC, 525 sync | Off | RL3, RL4, RL6, RL8, RL9 | EHT pulses present (pin 6) |
| 10 | 3.9 V | None | 10 mV | 525 NTSC, 525 sync | Off | RL3, RL4, RL7, RL8, RL9 | Not named on the measurement drawings; the pass/fail drawing gates step 10 with flag HF9 |
| 11 | End of sequence | Green PASS lamp if no failure has been latched; device supply switched off | |||||
Measurement circuits and limits
[edit | edit source]These are Ferranti's production test limits for a bare ZN401 in the test box, under the step conditions above (October and November 1983). They are not service voltages for a working TV80. The set-up voltages pencilled on the measurement board layout (1.5, 1.5 and 2.5 V, 2.7, 3.3, 2.88 and 3.52 V, and "VREF to 0.2" and "VREF to 0.5") match the comparator settings below.[15]
| Pin | Quantity | Step | Limit | Circuit | Flag |
|---|---|---|---|---|---|
| 14 | DC level, nominal "3V" | 3 | 2.7 to 3.3 V | ZN424 comparators 3 and 4 | HF3 |
| 9 | DC level, nominal "3.2V" | 3 | 2.88 to 3.52 V | ZN424 comparators 5 and 6 | HF3 |
| 12 | Supply current | 3 | Fed only from the 35 mA current source | ZN424 supply monitor | HF3' (written over HF6) |
| 17 | AGC | 1 | Below 2.5 V | ZN424 comparator 9 | HF1 |
| 17 | AGC | 8 | Above 1.5 V | ZN424 comparator 8 | HF8 |
| 11 | Sound, true RMS (AD536A) | 2 | Below 0.2 V | ZN424 comparator 1 | HF2 |
| 11 | Sound, true RMS (AD536A) | 4, 5, 7 | Comparator set to 0.5 V; the sheet heading says 1.5 V | ZN424 comparator 2 | HF4 (written over HF7) |
| 3 | Lock | 5 | Above 1.5 V | TL084 buffer and ZN424 comparator 7 | HF5, combined with the sound check |
| 6 | EHT pulses | 8, 9 | Pulses present to keep a 74122 retriggered (1 µF and 2K, "T = 1.4 ms") | 74122 monostable | Revised from HF8 and HF9 to HF9 and HF10 |
The flags are drawn high for a failure: the sheets label outputs "HI IF SOUND > 0.2V", "HI IF SOUND < 0.5V", "HI IF LOCK PIN <1.5V" and "HIGH WHEN EHT DOES NOT EXIST".[9][10] The AD536A averages with a 1 µF capacitor, and its thresholds come from a REF25Z 2.5 V reference through 20K presets.[10] In test 5, the lock comparator's output and the sound flag pass through 7400 gates to give HF5.[9]
None of the measurement circuits looks at the video output. The picture is left to the operator, through a "VIDEO FAIL" push-button on the pass/fail logic.[4]
Pass and fail logic
[edit | edit source]For each step, the inverted step line is combined in a 74L00 gate with that step's flag, and a 74L30 gathers all of them; a second 74L30 provides "extension I/P's", pulled up through 10K, for added tests. The strobe at the end of the settling time sets a fail latch if the current step's flag is high. The operator can also set the fail latch with the VIDEO FAIL button. A set fail latch lights the red "FAIL LAMP" through a ZTX500 and 150 Ω. If step 11 is reached with the fail latch clear, a pass latch sets and lights the green "PASS" lamp. A gate driven by both latches gives "HIGH SUPPLY OFF" to the power supply, so the device's supply is switched off when a failure is latched and at the end of a passing run. RESET clears both latches.[4][8]
ZN401 pin functions
[edit | edit source]The table gives every ZN401 pin that appears on Ferranti's drawings, with the function the FTV1 service manual gives for the same pin of IC1.
| Pin | FTV1 service manual (IC1) | Use on the test box drawings |
|---|---|---|
| 3 | In-lock detector | "Lock" voltage; must exceed 1.5 V in test 5 ("set lock range") |
| 6 | Converter drive: a pulse waveform to the power converter switching transistor TR4 | "EHT pulses", detected in tests 8 and 9 |
| 9 | 3.2 V temperature-compensated supply to the line hold and sound offset presets | DC level, nominal 3.2 V; 2.88 to 3.52 V in test 3 |
| 11 | Loudspeaker: output of the audio power amplifier | Sound output, measured as true RMS |
| 12 | VCC (pins 5 and 10 are ground) | Device supply, 3.9 to 6.5 V |
| 14 | 3 V d.c. varicap tuner supply | DC level, nominal 3 V; 2.7 to 3.3 V in test 3 (pin number corrected on the drawing) |
| 17 | AGC capacitor | AGC; below 2.5 V at 100 µV (test 1), above 1.5 V at 10 mV (test 8) |
| 18 | IF ground | IF ground |
| 19 | IF, the 230 MHz IF signal from the tuner | IF input, through 33 pF, terminated in 50 Ω |
| 21, 22 | Phase filter of the line hold phase-locked loop; shorting the pins lets the oscillator run at its natural frequency | Joined by a relay while RESET AND SYNC is held |
For a working set the service manual gives its own figures, measured on a set locked to a test signal with the volume at minimum: a 5.9 V ± 0.05 V supply, current no more than 95 mA (Issue 10 and 12 boards), and a 3 V reference supply of 3.0 V ± 150 mV, among others. Its specified supply range for the set is 4.7 to 6.5 V. When setting the line hold, it says to short IC pins 21 and 22 and adjust for a near-stationary picture.[6]
Points the documents leave unresolved
[edit | edit source]| Point | What the documents say |
|---|---|
| RL6 voltage | The power supply drawing sets the RL6 preset to 4.2 V. The relay table gives RL6 as "Vcc = 4.4V", and the power supply board layout labels the same preset 4.4 V, written over another figure. The documents disagree.[8][3][16] |
| Flag numbering | The pass/fail drawing of 12 October gates flags HF1 to HF5 with steps 1 to 5, HF6 with step 7, HF7 with step 8, HF8 with step 9 and HF9 with step 10. The measurement drawings of November renumber several flags: the sound flag from HF7 to HF4, the EHT detector's outputs from HF8 and HF9 to HF9 and HF10, and the supply monitor from HF6 to HF3'. They also add a tenth comparator in purple ink, giving HF7, whose input is marked only "(x)". The final link between steps 7 to 10 and their flags cannot be fixed from these sheets.[4][9][10][8] |
| Attenuator arithmetic | A 33 dB attenuator divides the voltage by about 44.7 (the drawing's title says "≈ 1/44"), which turns 10 mV into about 224 µV. The relay table calls the attenuated level 100 µV. The documents do not explain the difference.[12][3] |
| Sound threshold | The sound sheet's heading says the sound must exceed 1.5 V in tests 4, 5 and 7; the comparator for that check is set to 0.5 V. The scaling of the RMS converter's output is not shown.[10] |
| Attenuator title frequency | The attenuator drawing is titled for a frequency whose middle digit is unclear, 230 or 250 MHz. The FTV1 service manual and the 1986 review give the set's IF as 230 MHz.[12][6][7] |
| Pins 21 and 22 | The drawings do not say why the reset button joins these pins. The service manual's description of them is in the pin table above.[11][6] |
| The Philips instrument | The relay table puts RL2 "in Philips" without naming the instrument. The FTV1 service manual calls for a Philips 5519 pattern generator, or equivalent, when setting up a set; the test box documents do not mention it.[3][6] |
| Step button | As drawn, the sequencer runs one step per press of a front-panel button. The button's label is cut off at the sheet edge.[11] |
Documents in the archive
[edit | edit source]| Document | Date | What it is |
|---|---|---|
| TV-FER-MEM-156 | 25 November 1983 | Memo on building, commissioning and maintaining the ZN401 test boxes |
| TV-FER-SCH-157 | Undated | Power supply board layout |
| TV-FER-SCH-158 | Undated | Measurement board layout, with set-up voltages |
| TV-FER-SCH-159 | 12 October 1983 (issue label 30 September) | Power supply circuit |
| TV-FER-SCH-160 | Issue label 30 September 1983 | Driver for attenuator relays RL4A to RL4C |
| TV-FER-SCH-161 | Issue label 30 September 1983 | Drivers for RL1, RL2, RL5 to RL8, and RL3 and RL9 |
| TV-FER-SCH-162 | Issue label 30 September 1983 | RF attenuator and input switching |
| TV-FER-SCH-163 | 2 November (1983) | Circuits for tests 3, 5, 8 and 9 |
| TV-FER-SCH-164 | 18 November 1983 | Sound and AGC circuits |
| TV-FER-SCH-165 | 12 October 1983 | Sequencer logic |
| TV-FER-SCH-166 | 12 October 1983 | Pass/fail logic |
| TV-FER-DAT-167 | 28 September 1983 (issue label 30 September) | Typed relay functions and test step table |
| TV-FER-FOL-168 | Undated | The pink folder, labelled "ZN401 Test Box" |
Related pages
[edit | edit source]- Ferranti Archives 2026
- Ferranti Spectrum ULA Test Box, the other Ferranti test box in the archive
References
[edit | edit source]- ↑ Ferranti folder cover "ZN401 Test Box", Ferranti Archives 2026 (TV-FER-FOL-168). Source for the name of the file, which held documents TV-FER-MEM-156 to TV-FER-DAT-167.
- ↑ 2.0 2.1 Ferranti internal memo headed "ZN401 Test Box", from the Applications Manager, 25 November 1983, Ferranti Archives 2026 (TV-FER-MEM-156). Source for the urgent backlog of ZN401 devices awaiting test, the aim of commissioning several test boxes, and the temporary division of responsibility between the IC Applications and IC Test departments.
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 Ferranti typed relay table "Relays", "Sinclair TV Test Box Relays", 28 September 1983, issue label "TV TEST ISSUE 1 30/9/83", Ferranti Archives 2026 (TV-FER-DAT-167). Source for the function of relays RL1 to RL9 in their open and closed states, their locations, the relays closed in tests 0 to 10, and "Relay 8 is normally closed".
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 Ferranti ink schematic "Sinclair TV Test Box, Pass/Fail Logic", 12 October 1983, Ferranti Archives 2026 (TV-FER-SCH-166). Source for the gating of each step with its flag, "'0' & '6' go nowhere", the extension inputs, the strobe and fail latch, the VIDEO FAIL button, the red FAIL and green PASS lamps, the pass latch set at step 11, and the HIGH SUPPLY OFF output.
- ↑ 5.0 5.1 "TV80", Wikipedia (accessed 2026-10-18). Source for the names TV80, Flat Screen Pocket TV and FTV1, the September 1983 release, the flat CRT with side-mounted gun and Fresnel lens, and the sales of about 15,000.
- ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 Microvision Flat Screen Pocket TV (FTV1) service manual, transcribed text with circuit diagram and component layout, distributed as Sinclair_FTV1.zip with EEVblog #554 (accessed 2026-10-18). Source for IC1 marked "ZN 401E-2" on the circuit diagram, the IC pin functions (sections 3.4.2 to 3.4.17), the 4.7 to 6.5 V supply range, the 230 MHz IF, the receiving standards, the set-up checks (section 5.4) and the instruction to short IC pins 21 and 22 when setting the line hold.
- ↑ 7.0 7.1 Fred Blechman, "Tiny TVs", Modern Electronics, January 1986, pp. 22-26, with the sidebar "Single-Chip Television" on p. 24 (PDF). Source for the single-chip design, the chip being designed by Sinclair Research and produced by Ferranti on its FAB2 CDI process, the 230 MHz IF, the 625 and 525-line standards with 6.0, 5.5 and 4.5 MHz sound, and the digitally synthesised scan.
- ↑ 8.00 8.01 8.02 8.03 8.04 8.05 8.06 8.07 8.08 8.09 8.10 Ferranti ink schematic "Sinclair TV Test Box, Power Supply", 12 October 1983, issue label "TV TEST ISSUE 1 30/9/83", Ferranti Archives 2026 (TV-FER-SCH-159). Source for the ZN458 reference, the 6.5 V preset and the RL5, RL6 and RL7 presets labelled 4.5 V, 4.2 V and 3.9 V, the ZTX300 and ZTX450 followers to "Vcc PIN 12", the "HIGH FOR SUPPLY OFF" input, the 62 Ω and RL8 feed, the "SET 35mA" ZTX500 current source, and the ZN424 supply monitor with its red LED and flag HF3' (written over HF6).
- ↑ 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 Ferranti ink schematic "Sinclair TV Test Box, Tests 3, 5, 8 & 9 Circuits", dated 2 November (year cut off at the sheet edge), Ferranti Archives 2026 (TV-FER-SCH-163). Source for the pin 14 (3 V) and pin 9 (3.2 V) window comparators and their limits, the HF3 gate with the HF3' input, the pin 3 lock comparator "SET LOCK RANGE, PIN 3 >1.5V" and HF5, and the pin 6 "EHT PULSES" detector with its 74122 ("T = 1.4 ms") and outputs.
- ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 Ferranti ink schematic "Sinclair TV Test Box, Sound & AGC Circuits", 18 November 1983, Ferranti Archives 2026 (TV-FER-SCH-164). Source for "AGC range. Test 1 AGC must be < 2.5V. Test 8 AGC must be > 1.5V", the pin 17 comparators, "Sound. Test 2 must be < 0.2V. Test 4, 5, 7 must be > 1.5V", the AD536A on pin 11, the REF25Z reference, the comparator settings "VREF to 0.2V" and "VREF to 0.5V", the flags HF1, HF2, HF4 (written over HF7), HF5' and HF8, and comparator 10 in purple ink.
- ↑ 11.0 11.1 11.2 11.3 11.4 11.5 11.6 11.7 Ferranti ink schematic "Sinclair TV Test Box, Sequencer Logic", 12 October 1983, Ferranti Archives 2026 (TV-FER-SCH-165). Source for the front-panel button latch with its idle input, the 74121 monostables A (1.5 ms), B (about 200 ms) and C (1.5 ms, "STROBE") and their component values, the 74163 counter, 74154 decoder and 7447 "TEST NUMBER" display, and the "RESET AND SYNC BUTTON" with its 5 V relay joining pins 21 and 22.
- ↑ 12.0 12.1 12.2 12.3 12.4 12.5 12.6 Ferranti ink schematic "RF Attenuator Set To -33dB", issue label "TV TEST ISSUE 1 30/9/83", Ferranti Archives 2026 (TV-FER-SCH-162). Source for the two 75 Ω inputs and RL3, RL4A to RL4C, the 20, 10 and 3 dB sections, the 50 Ω carbon composition termination, the 33 pF coupling to "IF I/P PIN 19", "IF GND PIN 18", the copper ground plane and the 12 V coaxial relays.
- ↑ 13.0 13.1 Ferranti ink schematic "Relay driver for attenuator relays 4A, 4B, 4C", issue label "TV TEST ISSUE 1 30/9/83", Ferranti Archives 2026 (TV-FER-SCH-160). Source for the ZN74L30 gate on decoder lines 2 and 4 to 10, the three ZTX300 drivers, and the 12 V relay coils.
- ↑ 14.0 14.1 Ferranti ink schematics "Typical driver for relays 1, 2, 5, 6, 7 & 8" and "Driver for relays 3 & 9", issue label "TV TEST ISSUE 1 30/9/83", Ferranti Archives 2026 (TV-FER-SCH-161). Source for the gate-per-relay driver, the 5 V and 12 V coils, the LEDs and diodes, and decoder lines 6 to 10 for RL3 ("625/525 RF signal") and RL9 ("625/525 comp sync").
- ↑ Ferranti ink layout "Top View" of the Sinclair TV test box measurement board, undated, Ferranti Archives 2026 (TV-FER-SCH-158). Source for the board areas for tests 2, 3, 5 and 8 and AGC, the device-pin test points, and the set-up voltages on the 16-pin socket.
- ↑ Ferranti ink layout "Top View P.S.U. Sinclair TV Test Box", undated, Ferranti Archives 2026 (TV-FER-SCH-157). Source for the positions of RL5 to RL8 and the presets, the preset labelled 4.4 V written over another figure, and the connections "VCC Pin 12", 12 V, 5 V and "HIGH FOR SUPPLY OFF".