Cathode Corner SCTV Use and care manual

SCTV Scope Clock Kit
Assembly and User Manual
Copyright (C) 2022 Cathode Corner. All rights reserved.

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Table of Contents
Introduction ................................................................................................................................................. 5
Theory of Operation .................................................................................................................................... 6
PC Board Assembly .................................................................................................................................... 8
Cabinet Assembly ..................................................................................................................................... 14
Initial Checkout ......................................................................................................................................... 27
Final Assembly ......................................................................................................................................... 27
Using Your Clock ..................................................................................................................................... 31
Optional GPS receiver .............................................................................................................................. 32
Care of the Cabinet ................................................................................................................................... 32
Warranty ................................................................................................................................................... 32
Schematic Diagram ................................................................................................................................... 32

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Introduction
The Manual
This user manual is divided into sections. Not all sections are relevant to all users. The Theory of
Operation section is provided for the curious and may be skipped, as it is not necessary to know exactly
how the clock works in order to make it work.
The Clock
The SCTV scope clock is an electronic clock that displays the time and more on a small oscilloscope
tube using artfully drawn numbers. While most digital clocks use a seven-segment display optimized for
low cost and ease of manufacture, the SCTV is optimized for aesthetic appeal.
The clock is supplied with a laser-cut Plexiglass cabinet.
Contacting Cathode Corner
If you are having trouble assembling your clock, getting it to work, or you just want to talk with us about
clocks, you may contact Cathode Corner in any of the following ways.
Visit Cathode Corner on the Web at www.cathodecorner.com
Phone: [phone]
Email: [email protected]
Mailing address:
Cathode Corner
2560 E Ross Pl
Tucson AZ 85716
USA

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Theory of Operation
Power Supply
The power supply is of the switching type. 12V DC power is switched through a high-frequency
transformer to produce the necessary operating voltages. The power supply uses a unique topology to
drive the CRT and the logic circuits.
The most common types of switching power supplies are flyback and forward converters. A forward
converter uses the power driven when the primary switch is conducting, and multiplies that voltage by
the turns ratio. A flyback converter stores energy in the transformer while the switch is on, then transfers
that energy to the secondaries when the switch turns off.
This supply is both of these types in one - its outputs are all fed through voltage doublers, so that both
halves of the cycle are used. This is done to allow the voltage multiplier for the high voltage negative
supply to be regulated as well as the lower-voltage supplies.
The reason is that a forward converter develops a secondary voltage proportional to the turns ratio,
whereas a flyback converter develops a secondary voltage proportional to the duty cycle. These two
functions are different with regard to load, so a regulator for one will not be well regulated the other
way.
The switching IC is a National Semiconductor LM2586. It interrupts the current flowing through the
primary winding of T1 at a rate of 100 Kilohertz, and controls the duty cycle of this interruption to
provide regulated voltage outputs.
Moving on to the regulator, the deflection voltage is the one actually regulated. The other voltages
follow this voltage in proportion to their turns ratios. The regulator samples the deflection voltage
through a resistive divider.
The low-voltage supply provides -5V to the deflection amplifiers. The +5V supply is provided by a
linear regulator, because the switching supply doesn’t start up with a solid 5V to bring up the Teensy
computer reliably. This was an engineering change after problems wee found in a few of the kits sent to
early customers.
The filament supply is straight AC, since that heats up a wire as well as DC does. An AC-coupled
connection to the filament supply feeds a doubler which powers the optoisolator used for the modulation
signal. This optoisolator is a special logic-level photodiode unit with sub-microsecond switching time.
The Z modulation supply provides enough voltage to switch the grid on and off (~60VDC) and enough
current to do so quickly. A simple transistor switch controls the grid.
CRT Beam circuits
The CRT requires the correct DC voltages at all of its electrodes in order to form a bright yet small spot
on the screen. The cathode may be considered as the starting point of this system.
The grid requires a negative voltage relative to the cathode. This voltage is adjusted by the Intensity
control.
Blanking is active whenever the beam is being moved from one location to another. The computer tells
the blanking circuit when to blank the beam. Blanking is accomplished by switching the grid to a much
more negative voltage by the Z modulation circuit to cut off the beam.

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The focus anode requires about +500 volts with respect to the cathode. This voltage is adjustable over a
wide range to accommodate different CRTs with different focus voltage requirements.
The second anode requires about +1500V with respect to the cathode. This voltage is adjusted by the
Astigmatism control, which changes the second anode voltage with respect to the voltage on the
deflection plates, since the deflection plates have the secondary effect of acting as focusing lenses, first
in one axis then the other axis. The magnitude of this effect depends on the voltage on the second anode
relative to the average DC voltage on the deflection plates.
Deflection Amps
The deflection amps are push-pull Class A amplifiers, which strive to keep the voltage at the transistor's
emitter at 0.6V below its base by changing the current through the transistor. This in turn changes the
voltage at the collector, according to Ohm's Law. It's not a real fast circuit, but it works for clock use.
Numeric display
The digits are formed from circles, lines and arcs. The basic method of drawing a circle on a CRT is
called a Lissajous pattern. This is something that every student of electronics learns about early in
school, then promptly forgets. The only other known use of this numeric display technique is in the HP
1600 logic analyzer.
A Lissajous pattern is displayed by applying sine waves of different phases to the X and Y deflection
plates of a CRT. A sine wave on the Y plates and a cosine wave on the X plates give a circle. If the
phase difference is zero, then the circle collapses to a slanted line. If Y=0, the line is horizontal, etc.
Each character is made up of segments. Each segment has a center, a size code, and a dwell time. The
center places the segment within the digit's cell space. The size code indicates the X and Y radii of the
circle/ellipse, as well as if it will be a line (x=cos, y=cos) or a circle (x-cos, y=sin). The dwell time is
longer for larger circles to make the intensity appear consistent. An arc code tells the circuitry which
octants of the circle to blank out to make an arc, such as in the number 2.
Computer program
The software running on the computer is written in C for the Teensy, using the Arduino environment.
The program executes a main loop about 50 times per second, in sync with the mains frequency to
prevent electromagnetic interference from being visible in the display. Each display screen is built of a
draw list, with some extra parts that are drawn by special code such as the Tetris bucket and pieces, the
Pong paddles and the clock hands. Other code monitors the USB port for GPS data messages, and the
encoder knob for mode changes.
The code is open source. It resides at www.github.com/nixiebunny/SCTVcode
Optional GPS Input
An optional USB GPS connector allows the clock to take its timekeeping reference from the GPS
satellite constellation. The firmware automatically connects to the GPS receiver as long as it emits an
NMEA data stream at 4800 baud. The internal clock chip is reset to match GPS time every second, so
that the time will still be correct if GPS reception is lost.

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PC Board Assembly
Getting Started
Make sure that you have the following major parts:
SCTV printed circuit board (PCB) with surface-mount parts already installed
Anti-static bag with thru-hole PC board components
Ziploc bag with CRT and pot wiring parts
Ziploc bag with hardware
Seven laser-cut plastic pieces (coated in paper)
3RP1-A CRT
12V wall power adapter
If anything is missing, please contact Cathode Corner for assistance.
The PCB is provided with all the surface-mount parts already soldered to it. These parts are rather
difficult to solder without a lot of experience. The easy work is left for you to do.

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Board photo
A photograph of the top side of the assembled board is shown below. Refer to this photo to see how the
parts fit.
Tools needed
Soldering iron, fine tip, adjustable temperature preferred
Solder, high quality lead-free or leaded .031" diameter or smaller, rosin or no-clean flux
Small diagonal cutters
Small long-nose pliers
#1 Phillips screwdriver

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Parts List
The parts supplied in the kit are listed below in order of installation. 'Step' refers to the assembly
sequence. 'Marking' refers to any part number printed on the part itself. The assembly instructions begin
after the parts list. Note that the only parts that may be confused are the three trim pots. There are two
pots with the same value and a third with a different value, in case the numbers are too difficult to read.
PC Board parts
Step Qty Marking Description Designators
1 1 small Battery contact B1
2 1 big Battery holder B1
3 1 P6KE18A Diode, TVS D3
4 1 USB jack J9
5 1 504 Trim pot 500K R1
6 2 103 Trim pot 10K R2, R3
7 2 black Socket strip 24 pin for U2
8 1 black Socket strip 5 pin for U2
9 1 DC power jack J1
10 1 Header 6 pin .10" J5
11 1 Header 7 pin .10" J3
12 4 MPSW42 Transistor NPN Q2-Q5
13 1 Header 5 pin .156" J4
14 1 Header 6 pin .156" J2
15 2 1uF Capacitor 1uF 400V C29, C30
16 1 1.85A Fuse, PolySwitch F1
17 1 1000uF Capacitor 1000uF 25V C3
18 1 Rotary encoder S1
19 1 T-1596-01 Transformer T1
20 1 Heat sink for U1
21 2 Screws #4x1/4” for U1
22 1 Screw, 4-40x5/16” for U1
23 1 Thermal pad for U1
24 1 LM2586T Regulator U1
25 1 Lockwasher, #4 for U1
26 1 Hex nut, 4-40 for U1
27 1 7805 Regulator IC with cap. U7
28 1 black Wire, 1.5” long for U7
29 2 black 24 pin strip for U2
30 1 black 5 pin strip for U2
31 1 Teensy 3.6 Computer U2
32 1 CR2032 Battery B1

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Step by step guide
Since the clock has a transparent case, the effort you put into making sure that all the parts are installed
neatly will be reflected every time you or someone else looks at the clock. For this reason, it is
recommended that you take your time to ensure that every part is straight before soldering the second
pin. You can reheat a pin and move the part with your fingers to align it properly. This is the method
used for the factory-assembled clocks.
0) Check that the surface-mount part U8 is not installed. If it is installed, then remove it by heating the
side with two legs using a blob of solder, then prying it up a bit. Heat the leg on the other side and pry it
up a bit. Repeat until the part is off the board. Remove the excess solder so that the pads are mot shorted
together.
1 and 2) Install the small round battery contact in the center of the B1 footprint, then install the large
battery holder on top of it, with the open side facing the edge of the PC board. Solder them both.
3) Install and solder the P6KE18A diode D3 next. Bend the legs to a 90-degree angle first. Install the
diode with its striped end over the stripe shown on the board. Bend the legs apart at a 30-degree angle to
hold it in place while you solder it. Trim the excess leads with diagonal cutters.
4) Install the USB jack J9. Snap it into place, then be sure that it is straight instead of tilted. Solder one
of the big tabs first. Check that it’s still straight. Reheat and straighten it if not. Then solder the other big
tab and the four small pins.
5-6) Install the 500K trim pot R1 (marked 504) and the 10K trim pots R2 and R3 (marked 103). Spread
the legs on each of these pots after installing. Solder the center pin of each pot, then reheat this pin while
pressing the pot against the board, to ensure that it fits tightly against the board. Check also for square
alignment to the board to keep a neat appearance. After they are aligned, solder the remaining pins. Trim
the excess lead length.
7) Install and solder the long socket strips for U2 next. Place both strips in the board, turn it over and
solder one pin in the center of each strip. Then turn the board over and make sure that the strips are
straight. Then solder the remaining pins.
8) Install and solder the short socket strip in the middle of the U2 footprint. Again, solder one pin first,
make sure it’s straight, then solder the remaining pins.
9) Install the DC power jack J1. Solder the center pin, then reheat it and align the block so that it is
square and flush. Solder the other two pins.
10-11) Install the two small headers J3 and J5. Be sure that the plastic tab is towards the center of the
board. Solder one pin on each then check that they are fully seated. Reheat that pin while pressing down
on the header if needed to make it flush with the board. Solder the remaining pins.
12) Install and solder the MPSW42 transistors Q2-Q5 next. Cut them from the tape strip with the leads
as long as possible. Be sure to orient these parts with the flat side as shown on the board. Spread the
outer legs 30 degrees to hold them in place while soldering. Check and adjust the parts’ alignment after
soldering the center pin of each before finishing the soldering work. Trim the excess lead length.
13-14) Install the two large headers J2 and J4. Be sure that the plastic tab is towards the center of the
board. Solder one pin on each then check that they are fully seated. Solder the remaining pins.
15) Install and solder the 1uF electrolytic capacitors C29 and C30 next. Observe polarity! Note that the
Japanese manufacturers mark the negative lead of the electrolytic capacitors, but the PC board marks the

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positive hole with a + sign. The positive leads of the capacitors are longer. So put the long leads into the
plus holes. Bend the legs apart to hold them while soldering. Trim the excess lead length.
16) Install self-resetting fuse F1, bending the legs apart to hold it in place. Solder it. Trim the excess lead
length.
17) Install and solder the 1000uF capacitor C3 next. Put the long lead into the hole near the + sign. Trim
the excess lead length.
18) Install the rotary encoder S1. It snaps into place in the two large holes. Use care when snapping it
into place, so that all the small legs go into their holes. Ensure that it is aligned perpendicular to the
board, then solder it.
19) Install T1 next. You may have to straighten the leads to get them all to go into their holes. Make sure
it sits straight on the board, which may require work since one corner tends to sit higher than the others
due to the wires underneath it. Solder one pin on each side, then adjust it, then solder the remaining pins.
Trim the excess lead length.
20-21) Mount the heat sink for U1 using the two #4x1/4" self-tapping screws. Orient it with the notch
towards the board and the flat surface at the top. Blow all the metal filings off the board.
22-26) Put the 4-40 x 5/16” screw through the top hole of the heatsink from the capacitor side. Place the
beige thermal pad onto the screw. Place U21 into the holes in the board and onto the screw, while
holding the screw in place. Place the lockwasher and nut on the screw. Tighten the screw snug but not
real tight.
Solder the pins on U21.
27) A late change to the design has added a 7805 regulator IC to the bottom of the board, to improve
reliability of the power-on sequence. Remove the heat sink screw closest to the end of the board. Install
the 7805 regulator IC under this screw, with the legs over the F1 pads. Bend the leg without the
capacitor down so that it contacts the top of the F1 lead. Solder this pin to the F1 lead.

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28) Strip 1/8” of insulation from each end of the black wire. Solder one end to pin 3 of the 7805, the end
leg with the capacitor. Solder the other end to pin 48 of U2, the Teensy pin nearest the corner of the
board.
29) Press the two 24-pin strips into the socket strips at U2.
30) Press the five-pin strip into the socket at J8.
31) Place the Teensy on the pin strips at U2. Orient the Micro-USB end of the Teensy with the edge of
the board.
Solder the two 24-pin strips and the five-pin strip to the Teensy holes. Use care, as there isn’t much
room to work on the Teensy and it has many small parts that don’t want your soldering iron to touch
them. You may prefer to solder a few pins first, then remove the Teensy from the board and solder the
rest of the pins. (Apologies for making you do this work, the Teensys with pins were all sold out.)
31) Remove the CR2032 battery from its package by trimming away the paper area with scissors, then
insert it + side up into the B1 battery holder.
PC board assembly is complete.

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Cabinet Assembly
Introduction
This section describes the wiring of the clock controls and CRT, and the assembly of the clock into the
laser-cut Plexiglas cabinet. The wiring harnesses are made first, then the clock is assembled.
The wiring parts are packed in a separate bag. The wires are provided with pre-crimped terminals to
simplify assembly and assure durable connections. Do NOT insert the terminals into the connector shells
until instructed. If a terminal is inserted into the wrong shell hole, it may be removed by gently pushing
down with a 1/8" slot screwdriver blade on the little tang visible through the slot in the shell while
simultaneously pulling the wire gently out of the shell.
Each of the four control pots is soldered to a tiny cat-shaped PC board. Three wires from each pot are
terminated in two Molex connectors. The CRT socket has ten wires soldered to it, which are terminated
in two Molex connectors.
The cabinet assembly is the next step. The cabinet is made of seven pieces of laser-cut acrylic plastic.
The clock base is two identical pieces that are sandwiched together for added rigidity. The base holds
the PC board, the front and rear faces, and the cover. A bag of cabinet hardware is used to assemble the
cabinet.
The PC board is first mounted to the base assembly, then the front and rear faces are added to this. The
pots are installed and plugged in. The CRT socket is installed, the CRT clamp ring is installed, and the
CRT is installed. At this point, the clock is plugged in and tested. Then the CRT is aligned with the case
and its clamp tightened.
Next, the rear cup and cap pieces are installed (the tricky part). The cup is a small flexible piece that
protects the neck of the CRT. The cap is a flat piece that fits into the end of the cup. The front and rear
faces hold the controls and the CRT. Finally, the cover is installed over the clock.
Tools needed
1/16” hex driver or ball driver
Slip-joint pliers
5/16” wrench or nutdriver
#1 Phillips screwdriver
#2 Phillips screwdriver
Small file
Roll of duct tape or Gorilla tape (for peeling paper from laser-cut plastic)
Cabinet wiring parts
There is a bag of cabinet wiring parts provided, the bag with the wires. Check that all parts listed below
are present.
Separate the wires carefully by length, as there are six different groups of wires that are soldered to
different things. The pot wires have small gold Molex pins, while the CRT socket wires have large tin
Molex pins.

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2 103L 10K pots Pos
1 504L 500K pot Brightness
1 105L 1M pot Focus
4 Kitty Pot PC boards
3 H pos 6" wires: brown, red, orange
3 V pos 4" wires: yellow, green, blue
3 Focus 8" wires: brown, red, orange
3 Brightness 7" wires: green, blue, violet
1 white CRT socket
5 CRT defl 11.5" wires: blue, violet, grey, black, white, with large pins
5 CRT gun 7.5" wires: brown, red, orange, yellow, green, with large pins
10 3/16” dia ½” long pieces of heat shrink tubing
1 Shell, Molex, 6 pin .156” P2
1 Shell, Molex, 5 pin .156” P4
1 Shell, Molex, 6 pin .10” P5
1 Shell, Molex, 7 pin .10” P3
Control Wiring
Each of the four control pots is a blue square with a white shaft. The two pots with long shafts are the H
position and V position pots. Their shafts need to be cut to length with diagonal cutters. The place to cut
is ¼” from the end of the shaft, about where the flat spot begins. After cutting the shafts, clean the burrs
off the end with a small file.
Each of the pots is soldered to a tiny, round PC board with cat ears. The pot is inserted into the board on
the side with the white square. This work is done most easily by putting two pots in a vise, one near each
end of the jaws with the pins pointing skyward. Place a cat PC board over the pot with the white square
down, so that the square is facing the pot. Solder the three pins, then trim the leads flush. Repeat for the
other two pots.
Each pot has a small number identifying its value. Be sure to use the two labeled 103L (with the cut
shafts) for the H pos and V pos controls. 504L is the Brightness pot. 105L is the Focus pot.
V pos pot board
Find the three 4” long yellow, green and blue wires. Strip 1/4" of insulation off the free end of each
wire. Tin the bare ends of the wires with solder, being careful to remove any blobs.
Mount a kitty board with a 103L pot in the vise with the pot facing up and/or away from you. A 45
degree angle works well if your vise is adjustable. Insert the yellow wire into the hole marked 1, with
the insulation on the pot side of the board. Solder it from below/front.
Install the green wire in hole 2 and solder it. Install the blue wire in hole 3 and solder it. Trim the
soldered wires with diagonal cutters. Set aside this wired board.
H pos pot board
Find the three 6” long brown, red and orange wires. Strip 1/4" of insulation off the free end of each wire.
Tin the bare ends of the wires with solder, being careful to remove any blobs.
Mount the other kitty board with 103L pot in the vise. Insert the brown wire into the hole marked 1, with
the insulation on the pot side of the board. Solder it from below/front.

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Install the red wire in hole 2 and solder it. Install the orange wire in hole 3 and solder it. Trim the
soldered wires with diagonal cutters. Set aside this wired board.
Brightness pot board
Find the three 7” long green, blue and violet wires. Strip 1/4" of insulation off the free end of each wire.
Tin the bare ends of the wires with solder, being careful to remove any blobs.
Mount the kitty board with 504L pot in the vise. Insert the violet wire into the hole marked 1, with the
insulation on the pot side of the board. Solder it from below/front.
Install the blue wire in hole 2 and solder it. Install the green wire in hole 3 and solder it. Trim the
soldered wires with diagonal cutters. Set aside this wired board.
Focus pot board
Find the three 8” long brown, red and orange wires. Strip 1/4" of insulation off the free end of each wire.
Tin the bare ends of the wires with solder, being careful to remove any blobs.
Mount the remaining kitty board with 105L pot in the vise. Insert the orange wire into the hole marked
1, with the insulation on the pot side of the board. Solder it from below/front.
Install the red wire in hole 2 and solder it. Install the brown wire in hole 3 and solder it. Trim the
soldered wires with diagonal cutters. Set aside this wired board.
Position pot connector
On each of the four pot boards, twist the three wires around each other to form a twisted triad. See the
picture below. Bend the wires down around the pot board so that they exit parallel to the board.
Find the small 6 pin header block. Orient it so that the large holes are facing you, and the small slots are
at the top. This places pin 1 at the left end. You will insert the little terminals into this block with the
tiny tab facing up. The pins need to be inserted with the pin aimed up slightly so that it will slide into an
internal groove in the block. Don’t force it if it won’t slide in; pull it out and try again at a different
angle. The pin will snap into place when properly guided in and seated.

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Insert the little terminals into this block as shown in the chart below.
Pin Wire
1 Brown
2 Red
3 Orange
4 Yellow
5 Green
6 Blue

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Bright/Focus pot connector
Find the small 7 pin header block. Orient it so that the large holes are facing you, and the small slots are
at the top. This places pin 1 at the left end.
Insert the little terminals into this block as shown in the chart below.
Pin Wire
1 Brown
2 Red
3 Orange
5 Green
6 Blue
7 Violet

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CRT socket wiring
The kit is supplied with 10 different colored pieces of wire, each with a large Molex pin crimped to one
end. Strip 1/4" of insulation off the unterminated end of each wire.
Clamp the white CRT socket in the vise with the terminal pins facing you and pin 2 pointing down.
There is a pin number molded into the ceramic next to each pin. Pin 1 is to the left of the notch in this
orientation, and pin 12 is to the right of the notch.
Solder the wires to the CRT pins per the table below. Bend each wire's bare end into a V shape and hook
it through the socket terminal, then squeeze it around the terminal, to ensure a tight mechanical
connection. Start with pin 12 and orient the wires such that they curl downward from the CRT socket.
Rotate the socket in the vise 180 degrees before soldering pins 6-10, so that the pin being soldered is
always near the bottom.
Color CRT Pin
Red 12
Orange 1
Brown 2
Yellow 3
Green 4
Grey 6
Violet 7
Blue 8
Black 9
White 10

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Slide one piece of heat-shrink tubing over each wire on the CRT socket, making sure that each piece is
seated against the socket. Shrink all the tubing pieces onto the CRT socket terminals using a match or
lighter for heat, or a heat gun if you have one. It is best to hold the socket assembly by the wires when
doing this, so that you don't burn your fingers. Don't worry, the heat shrink tubing is flameproof.
Clamp the socket in the vise again, then twist together the two wires in each of the following three pairs
of CRT wires. Twist them by holding both wires out at a 20-degree angle from each other, then passing
one over the other repeatedly until they’re in a single cable with about 2 twists per inch.
Violet-Grey
White-Black
Red-Orange
Plug the Molex pins into the large 5-pin and 6-pin connector shells per the table below, using the
photograph above for reference. Again, hold the shell with the large opening facing you and the slots at
the top. In this orientation, pin 1 is on the left end.
Shell Pin Color
6 pin 1 Brown
6 pin 2 Red
6 pin 3 Orange
6 pin 4 Yellow
6 pin 5 -
6 pin 6 Green
5 pin 1 Blue
5 pin 2 Violet
5 pin 3 Grey
5 pin 4 White
5 pin 5 Black