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Mercury 30A Ham Radio SMPS

Mercury 30A SMPS
Mercury 30A SMPS

After having a couple of the cheap Chinese PSUs fail on me in a rather spectacular fashion, I decided to splash on a more expensive name-brand PSU, since constantly replacing PSUs at £15 a piece is going to get old pretty fast. This is the 30A model from Mercury, which seems to be pretty well built. It’s also significantly more expensive at £80. Power output is via the beefy binding posts on the front panel. There isn’t any metering on board, this is something I’ll probably change once I’ve ascertained it’s reliability. This is also a fixed voltage supply, at 13.8v.

Rear Panel
Rear Panel

Not much on the rear panel, just the fuse & cooling fan. This isn’t temperature controlled, but it’s not loud. No IEC power socket here, the mains cable is hard wired.

Main Board
Main Board

Removing some spanner-type security screws reveals the power supply board itself. Everything on here is enormous to handle the 30A output current at 13.8v. The main primary side switching transistors are on the large silver heatsink in the centre of the board, feeding the huge ferrite transformer on the right.

Transformer
Transformer

The transformer’s low voltage output tap comes straight out instead of being on pins, due to the size of the winding cores. Four massive diodes are mounted on the black heatsinks for output rectification.

 

SMPS Controller
SMPS Controller

The supply is controlled via the jelly bean TL494 PWM controller IC. The multi-turn potentiometer doesn’t adjust the output voltage, more likely it adjusts the current limit.

Standby Supply
Standby Supply

Power to initially start the supply is provided by a small SMPS circuit, with a VIPer22A Low Power Primary Switcher & small transformer on the lower right. The transformer upper left is the base drive transformer for the main high power supply.

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Thorn Ultra 6816 B&W CRT TV Teardown

Thorn Ultra 6816
Thorn Ultra 6816 (Stock Photo)

The other day at the local canal-side waterpoint, this TV was dumped for recycling, along with another later model Colour TV. This is a 1970’s Black & White mains/battery portable made by Thorn. It’s based on a common British Radio Corporation 1590 chassis. Having received a soaking from rain, I didn’t expect this one to work very well.

Tuner
Tuner

Being so old, there is no electronic control of the tuner in this TV, and only has the capability to mechanically store 4 different channels. The tuner itself is a cast box with a plastic cover.

Tuning Lever
Tuning Lever

The mechanical buttons on the front of the TV push on this steel bar, by different amounts depending on the channel setting. This bar is connected to the tuning capacitor inside the tuner.

Tuner Compartments
Tuner Compartments

Unclipping the plastic cover, with it’s lining of aluminium foil for shielding reveals the innards of the tuner module.

Tuner Input Stage
Tuner Input Stage

Here’s the tuner front end RF transistor, which has it’s can soldered into the frame, this is an AF239 germanium UHF transistor, rated at up to 900MHz.

Tuner IF Mixer Stage
Tuner IF Mixer Stage

As the signal propagates through the compartments of the tuner, another transistor does the oscillator / IF mixing, an AF139 germanium, rated to 860MHz.

Tuning Capacitor
Tuning Capacitor

As the buttons on the front of the set are pushed, moving the lever on the outside, the tuning capacitor plates intermesh, changing the frequency that is filtered through the tuner. The outer blades of the moving plates are slotted to allow for fine tuning of the capacitance, and therefore transmitted frequency by bending them slightly.

Mains Transformer
Mains Transformer

Being a dual supply TV that can operate on either 12v battery power or mains, this one has a large centre tapped mains transformer that generates the low voltage when on AC power. Full wave rectification is on the main PCB. The fuse of this transformer has clearly been blown in the past, as it’s been wound with a fine fuse wire around the outside to repair, instead of just replacing the fuse itself.

Chassis Rear
Chassis Rear

The back of the set has all the picture controls on the bottom edge, with the power input & antenna connections on the left just out of shot. The CRT in this model is an A31-120W 12″ tube, with a really wide deflection angle of 110°, which allows the TV to be smaller.

Main PCB
Main PCB

The bottom of the mainboard has all the silkscreen markings for the components above which certainly makes servicing easier 😉 This board’s copper tracks would have been laid out with tape, obviously before the era of PCB design software.

Components
Components

The components on this board are laid out everywhere, not just in square grids. The resistors used are the carbon composition type, and at ~46 years old, they’re starting to drift a bit. After measuring a 10K resistor at 10.7K, all of these would need replacing I have no doubt. Incedentally, this TV could be converted to take a video input without the tuner, by lifting the ferrite beaded end of L9 & injecting a signal there.

Flyback Primary Windings
Flyback Primary Windings

The flyback (Line Output Transformer) is of the old AC type, with the rectifier stack on top in the blue tube, as opposed to more modern versions that have everything potted into the same casing. The primary windings are on the other leg of the ferrite core, making these transformers much more easily repairable. This transformer generates the 12kV required for the CRT final anode, along with a few other voltages used in the TV, for focussing, etc.

Rectifier Stack
Rectifier Stack

The main EHT rectifier stack looks like a huge fuse, inside the ceramic tube will be a stack of silicon diodes in series, to withstand the high voltage present.

Horizontal Output Transistor
Horizontal Output Transistor

This is the main switching transistor that drives the flyback, the HOT. This is an AU113, another germanium type, rated at 250v 4A. The large diode next to the transistor is the damper.

I’ve managed to find all the service information for this set online, link below!
[download id=”5616″]
More to come if I manage to get this TV working!

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Panasonic NV-M5 VHS Camcorder Teardown

Overview

Panasonic NV-M5 Camera
Panasonic NV-M5 Camera

Time foe some more retro tech! This is a 1980’s vintage CCD-based VHS camcorder from Panasonic, the NV-M5. There are a lot of parts to one of these (unlike modern cameras), so I’ll split this post into several sections to make things easier to read (and easier to keep track of what I’m talking about :)).

Left Side
Left Side

The left side of the camera holds the autofocus, white balance, shutter speed & date controls.

Left Side Controls
Left Side Controls
Lens Adjustments
Lens Adjustments

The lens is fully adjustable, with either manual or motorized automatic control.

Rear Panel
Rear Panel

The back panel has the battery slot, a very strange looking DC input connector, remote control connector & the earphone jack.

Top Controls
Top Controls

The top panel of the camera holds the main power controls, manual tape tracking & the tape transport control panel.

Viewfinder
Viewfinder

The viewfinder is mounted on a swivel mount. There’s a CRT based composite monitor in here. Hack ahoy!

Camera Section

Process Board Assembly
Process Board Assembly

Here’s the camera section of the camcorder, and is totally packed with electronics! There’s at least half a dozen separate boards in here, all fitted together around the optics tube assembly.

AWB PCB
AWB PCB

On the top of the assembly is the Automatic White Balance PCB. Many adjustments here to get everything set right. Not much on the other side of this board other than a bunch of Op-Amps. The iris stepper motor is fitted in a milled opening in the PCB, this connects to one of the other PCBs in the camera module.

AWB Sensor
AWB Sensor

Here’s the AWB sensor, mounted next to the lens. I’m not all to certain how this works, but the service manual has the pinout, and there are outputs for all the colour channels, RGB. So it’s probably a trio of photodiodes with filters.

Focus & Zoom Motors
Focus & Zoom Motors

Focus & Zoom are controlled with a pair of DC gear motors. The manual operation is feasible through the use of slip clutches in the final drive pinion onto the lens barrel.

Process Board
Process Board

The main camera section process board is above. This board does all the signal processing for the CCD, has the bias voltage supplies and houses the control sections for the motorized parts of the optics assembly. There are quite a few dipped Tantalum capacitors on pigtails, instead of being directly board mounted. This was probably done due to space requirements on the PCB itself.2016-08-20_13-40-11_000357

Under the steel shield on this board is some of the main signal processing for the CCD.

Optics Assembly
Optics Assembly

The back of the optics tube is a heavy casting, to supress vibration. This will be more clear later on.

Position Sensor Flex
Position Sensor Flex

The position of the lens elements is determined by reflective strips on the barrel & sensors on this flex PCB.

Sub Process Board
Sub Process Board

There’s another small board tucked into the side of the tube, this hooks into the process PCB.

Process Delay Line
Process Delay Line

According to the schematic, there’s nothing much on this board, just a delay line & a few transistors.

Piezo Focus Disc
Piezo Focus Disc

Here’s the reason for the heavy alloy casing at the CCD mounting end of the optics: the fine focus adjustment is done with a piezoelectric disc, the entire CCD assembly is mounted to this board. Applying voltage to the electrodes moves the assembly slightly to alter the position of the CCD. The blue glass in the centre of the unit is the IR filter.

IR Relective Sensors
IR Relective Sensors

The barrel position sensors are these IR-reflective type.

Iris Assembly
Iris Assembly

The iris is mounted just before the CCD, this is controlled with a galvanometer-type device with position sensors incorporated.

Iris Opening
Iris Opening

Pushing on the operating lever with the end of my screwdriver opens the leaves of the iris against the return spring.

Tape Transport & Main Control

Main Control Board
Main Control Board

Tucked into the side of the main body of the unit is the main system control board. This PCB houses all the vital functions of the camera: Power Supply, Servo Control, Colour Control,Video Amplifiers, etc.

Tape Drum
Tape Drum

Here’s the main tape transport mechanism, this is made of steel & aluminium stampings for structural support. The drum used in this transport is noticeably smaller than a standard VHS drum, the tape is wrapped around more of the drum surface to compensate.

Tape Transport
Tape Transport

The VHS tape sits in this carriage & the spools drive the supply & take up reels in the cartridge.

Main Control PCB
Main Control PCB

Here’s the component side of the main control PCB. This one is very densely packed with parts, I wouldn’t like to try & troubleshoot something like this!

Main PCB Left
Main PCB Left

The left side has the video head amp at the top, a Panasonic AN3311K 4-head video amp. Below that is video processing, the blue components are the analogue delay lines. There are a couple of hybrid flat-flex PCBs tucked in between with a couple of ICs & many passives. These hybrids handle the luma & chroma signals.
Top left is the capstan motor driver a Rohm BA6430S. The transport motors are all 3-phase brushless, with exception of the loading motor, which is a brushed DC type.

Delay Line
Delay Line

Here’s what is inside the delay lines for the analogue video circuits. The plastic casing holds a felt liner, inside which is the delay line itself.

Internal Glass
Internal Glass

The delay is created by sending an acoustic signal through the quartz crystal inside the device by a piezoelectric transducer, bouncing it off the walls of the crystal before returning it to a similar transducer.

Main PCB Centre
Main PCB Centre

Here’s the centre of the board, the strange crystal at bottom centre is the clock crystal for the head drum servo. Why it has 3 pins I’m not sure, only the two pins to the crystal inside are shown connected on the schematic. Maybe grounding the case?
The main servo controls for the head drum & the capstan motor are top centre, these get a control signal from the tape to lock the speed of the relative components.

Main PCB Right
Main PCB Right

Here’s the right hand side. The main power supply circuitry is at top right, with a large can containing 4 switching inductors & a ferrite pot core transformer. All these converters are controlled by a single BA6149 6-channel DC-DC converter controller IC via a ULN2003 transistor array.
The ceramic hybrid board next to the PSU has 7 switch transistors for driving various indicator LEDs.
The large tabbed IC bottom centre is the loading motor drive, an IC from Mitsubishi, the M54543. This has bidirectional DC control of the motor & built in braking functions. The large quad flat pack IC on the right is the MN1237A on-screen character generator, with the two clock crystals for the main microcontroller.

Erase Head
Erase Head

The full erase head has it’s power supply & oscillator on board, applying 9v to this board results in an AC signal to the head, which erases the old recording from the tape before the new recording is laid down by the flying heads on the drum.

Audio Control PCB
Audio Control PCB

The Audio & Control head is connected to this PCB, which handles both reading back audio from the tape & recording new audio tracks. The audio bias oscillator is on this board, & the onboard microphone feeds it’s signal here. The control head is fed directly through to the servo section of the main board.

Drum Motor
Drum Motor

The motor that drives the head drum is another DC brushless 3-phase type.

Hall Sensors
Hall Sensors

These 3 Hall sensors are used by the motor drive to determine the rotor position & time commutation accordingly.

Stator
Stator

The stator on this motor is of interesting construction, with no laminated core, the coils are moulded into the plastic holder. The tach sensor is on the side of the stator core. This senses a small magnet on the outside of the rotor to determine rotational speed. For PAL recordings, the drum rotates at 1500 RPM.

Motor Removed
Motor Removed

Not much under the stator other than the bearing housing & the feedthrough to the rotary transformer.

Head Disc
Head Disc

The heads are mounted onto the top disc of the drum, 4 heads in this recorder. The signals are transmitted to the rotating section through the ferrite rotary transformer on the bottom section.

Head Chip
Head Chip

The tiny winding of the ferrite video head can just about be seen on the end of the brass mounting.

Capstan Motor Components
Capstan Motor Components

The capstan motor is similar to the drum motor, only this one is flat. The rotor has a ferrite magnet, in this case it wasn’t glued in place, just held by it’s magnetic field.

Capstan Motor Stator
Capstan Motor Stator

The PCB on this motor has a steel backing to complete the magnetic circuit, the coils for the 3 motor phases are simply glued in place. The Hall sensors on this motor are placed in the middle of the windings though.
Again there is a tach sensor on the edge of the board that communicates the speed back to the controller. This allows the servo to remain locked at constant speed.

Viewfinder

Viewfinder Assembly
Viewfinder Assembly

As usual with these cameras, this section is the CRT based viewfinder. These units take the composite signal from the camera to display the scene. This one has many more pins than the usual viewfinder. I’ll hack a manual input into this, but I’ll leave that for another post.

Viewfinder Circuits
Viewfinder Circuits

Being an older camera than the ones I’ve had before, this one is on a pair of PCBs, which are both single-sided.

Main Viewfinder Board
Main Viewfinder Board

The main board has all the power components for driving the CRT & some of the adjustments. The main HV flyback transformer is on the right. This part creates both the final anode voltage for the tube & the focus/grid voltages.

Viewfinder Control PCB Top
Viewfinder Control PCB Top

The viewfinder control IC is on a separate daughter board in this camera, with two more controls.

Control IC
Control IC

The control IC is a Matsushita AN2510S, this has all the logic required to separate the sync pulses from the composite signal & generate an image on the CRT.

Viewfinder CRT Frame
Viewfinder CRT Frame

The recording indicator LEDs are mounted in the frame of the CRT & appear above the image in the viewfinder.

Viewfinder CRT With Yoke
Viewfinder CRT With Yoke

Here the CRT has been separated from the rest of the circuitry with just the deflection yoke still attached.

M01JPG5WB CRT
M01JPG5WB CRT

The electron gun in this viewfinder CRT is massive in comparison to the others that I have seen, and the neck of the tube is also much wider. These old tubes were very well manufactured.

Viewfinder Optics
Viewfinder Optics

A simple mirror & magnifying lens completes the viewfinder unit.

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eBay Flyback High Voltage PSU

Flyback PSU
Flyback PSU

I have found myself needing some more in the way of High Voltage supplies of late, with the acquisition of the new He-Ne laser tubes, so I went trawling eBay for something that would be suitable to run these tubes. (I currently only have a single He-Ne laser PSU brick, and they’re notoriously hard to find & rather expensive).
This supply is rated at 1kV-10kV output, at 35W power level. Unfortunately this supply isn’t capable of sustaining the discharge in a large He-Ne tube, the impedance of the supply is far too high. Still, it’s useful for other experiments.
The flyback-type transformer clearly isn’t a surplus device from CRT manufacture, as there are very few pins on the bottom, and none of them connect to the primary side. The primary is separately wound on the open leg of the ferrite core.

Drive Electronics
Drive Electronics

The drive electronics are pretty simple, there’s a controller IC (with the number scrubbed off – guessing it’s either a 556 dual timer or a SMPS controller), a pair of FDP8N50NZ MOSFETs driving the centre-tapped primary winding.
The drive MOSFETs aren’t anything special in this case: they’re rated at 500v 8A, 850mΩ on resistance. This high resistance does make them get rather hot even with no load on the output, so for high power use forced-air cooling from a fan would definitely be required.

Test Setup
Test Setup

Here’s the supply on test, I’ve got the scope probes connected to the gate resistors of the drive MOSFETs.

Waveforms
Waveforms

On the scope the primary switching waveforms can be seen. The FETs operate in push-pull mode, there’s a bit of a ring on the waveform, but they’re pretty nice square waves otherwise.

Arc
Arc

At maximum power on 12v input, about 25mm of gap is possible with an arc.

Modular He-Ne Laser Power Supply

Description and Schematic

SG-HM2 is a modular He-Ne laser power supply based on IC-HI1 with some minor enhancements. The first version is for laser tubes up to approximately 1 mW (2 mW with trivial modifications) but it should be straightforward to go to 5 mW or even higher power tubes by replacing the SG-HM2 HV Module (HVM2-1) with one with a higher voltage and current rating, along with a higher power MOSFET and minor component value changes to the Control Module (suggestions below). I have added an adjustment for tube current, a current limiting resistor and Zener to protect against output short circuits, an enable input (ground to turn on), a bleeder resistor to virtually eliminate the shock hazard after the power supply is turned off, and power and status LEDs.

  • Get the schematic for SG-HM2 (1 mW version) in PDF format: [download id=”5610″]

Modifying SG-HM2 for Higher Power He-Ne Laser Tubes

The following are guidelines for modifying SG-HM2 to drive various power He-Ne lasers. The PCB layout below with two versions of the HV Module should accommodate He-Ne laser tubes up to 10 mW. All assume input of around 12 V though a higher power system can generally run lower power lasers at reduced input voltage. If operation at rated power on another input voltage is desired, the number of turns on the inverter transformer can be adjusted accordingly. As noted above, the 1 mW HV Module (HVM2-1) should run tubes up to about 2 mW, though increasing the µF values of some of the HV capacitors may be desirable to reduce ripple at the higher tube current. Minor changes may also be needed in the components on the SG-HM2 Control Module including using a higher power MOSFET for Q1 and reducing the values of R7 and/or R8 for the higher tube current. Or, just populate the Control Module with Q1 being an IRF644, R7 being 150 ohms, and R8 being 750 ohms for compatibility with all the HV modules. For that matter, the HVM2-5 PCB HV Module should be usable with lower power lasers.

SG-HM2 Inverter Transformer

The inverter transformer for HVM2-1 is wound on a ferrite pot core with a small air-gap (about 0.005″). It is 18 mm in diameter by 11 mm high. While specified to use a 9 turn primary and 450 turn secondary, these values can be adjusted somewhat to handle various input and output requirements. Don’t go much lower on the primary as this may result in core saturation. The 9/450 transformer should be fine for 1 to 2 mW He-Ne laser tubes running on 8 to 15v DC input. With 9/300, it will operate on about 12 to 20v DC. Increasing the number of secondary turns (e.g., 9/600) may result in operation on a slightly lower input voltage, but probably not by much. The 9/450 transformer may even run He-Ne laser tubes larger than 2 mW but I haven’t yet tested this since I haven’t built a prototype of HVM2-5 as yet.

It doesn’t matter very much whether the primary (P) is wound first or the secondary (S) is wound first though the former appears to work slightly better, running the tube at about 8v DC input instead of 9v DC input for the same 9/450 transformer. P over S is slightly easier to wind since the primary doesn’t get in the way and increase the lumpiness of the secondary layers. However, with S over P, insulation is somewhat less critical since the HV lead is out away from anything else. With the P over S, additional insulation is needed between them. Also, since the primary coil is larger diameter, it will have more resistance and there will be greater inter-winding capacitance (though probably not significant). The secondary should be constructed as multiple layers of about 50 or 60 turns each, with insulating tape between layers. Each should be wound in as close to a single layer as possible with alternating layers staggered to prevent arc-over. This doesn’t have to be perfect but try to go gradually from one side to the other to keep wires at high relative potential away from each other. Make sure the HV output leads (particularly the one away from the dot) are well insulated as they exit the transformer. And, as noted, if the primary is over the secondary, there must be high voltage insulation between them. The peak output voltage when the MOSFET turns off (the flyback pulse) may be more than 5 times higher than what would be expected from the DC input voltage and the turns-ratio alone – several kV and this *will* try to find a path to ground! There are more detailed transformer construction instructions in the next section.

Note that this transformer is slightly larger physically than the one from IC-HI1. This is for two reasons: (1) It is easier to wind with more space and a larger wire size for the secondary, and (2) continuous operation should be possible with 2 mW laser tubes, which might have been marginal with the original transformer used in IC-HI1. A by-product of the larger core is that its 9 turn primary should be roughly equivalent to the 12 turn primary of the smaller core in terms of inductance and core saturation limitations.

Interestingly, a similar transformer found in a different commercial power supply, had no insulating tape anywhere. It would appear that with very precise machine-wound HV secondary, done first, the voltage is distributed so uniformly that this is unnecessary.

I’ve now built and tested several transformers in IC-HI1, removing the original transformer and installing socket pins so either the original or an adapter board can be plugged in. This setup is then equivalent to SG-HM2 with the HVM2-1 HV Module. The minimum input voltage values that follow are when driving a 0.5 mW He-Ne laser tube:

*The number of turns on the original (#1) is not really known exactly and may be lower or higher by up to 25 percent based on the measured secondary resistance (45 ohms) and estimated wire size (somewhere between #38 and #40. (Even with the larger wire, the amount of bobbin area taken up by the wire is less than 50 percent so it should fit even with many layers of insulating tape. The transformer is Epoxy impregnated and likely to be impossible to disassemble into any form that can be analyzed!)

All of these transformers will drive He-Ne laser tubes of up to at least 2.5mW using the equivalent of the HVM2-1 HV Module which is part of IC-HI1. Even with the 2.5mW tube, the minimum operating voltage was only about 0.5v higher than for the 0.5mW tube. There is a good chance they would drive even larger He-Ne laser tubes (though possibly at a slightly higher input voltage) but I don’t dare try using the existing HV circuitry as it might not survive for long. I suspect that transformers #4, #5, and #6 would run on an input voltage of less than 8v DC but the salvaged cores I am using have a larger air-gap than might be optimal and I don’t have anything to reduce it without heavy losses. They attempt to start the tube at around 6v DC but are unable to maintain it and flicker rapidly. (#2 and #3, which use the same style core, would also benefit somewhat.) Operation using #1 and #5 is virtually identical, with the original running at perhaps 0.5v DC less input. I expect they would be even more identical if the air-gap on #5 were smaller, and #6 with its smaller air-gap does indeed run at the lower input voltage. I haven’t actually confirmed that anything blows up above the maximum voltages listed above, which were arbitrarily chosen. But I am guessing that bad things might happen at some point. 🙂

I have also constructed a transformer which will need to be used with HVM2-5: 12/1200, P over S, on a 30×19 pot core. I will also construct a 9/900. S over P, on a 30×19 pot core (or on a 26×16 if I can find one). Testing of these will have to await an HVM2-5 prototype.

SG-HM2 Transformer Construction

Here are details on construction of the inverter transformer for SG-HM2. With all parts and tools on hand, it takes about an hour start to finish. Only a small portion of this time is in the actual winding (at least if a coil winding machine is used). Most of the time is spent in adding the insulation tape and terminating the leads. After constructing a few of these, it does go quicker. 🙂

Step-by-step instructions are provided for the HVM2-1 transformer. The changes needed for HVM2-5 are summarized at the end of this section. Some sort of coil winding machine is almost essential as #40 wire is extremely thin and easy to break. (Anything larger than #40 will not fit on the bobbin.) It doesn’t have to be fancy. Mine is probably 50 years old of the type that is (used to be?) advertised in the back of electronics magazines. However, a couple of spindles – one that is fixed or free to rotate for the wire supply and the other which can be turned for the coil being wound – are really all that are needed. Don’t use any sort of powered approach though (unless you have a *real* professional coil winder!) as it is all too easy to break the wire if there is no tactile feedback to detect snags.

  1. Parts required for T101 of HVM2-1:
    • 18×11 mm (1811) ferrite pot core with a small air-gap (no more than 0.005″) or no air-gap, and a single section bobbin. These are available from several manufacturers but surplus or salvaged cores may be easier to obtain. Radio Shack used to have a “ferrite kit” which included a variety of sizes of cores (only 1 each though so you’d have to buy two kits and there were no bobbins!). I doubt the kit still exists though.
    • Approximately 1.5 feet of #28 magnet wire for the primary (9 turns wound first) and approximately 60 feet of #40 magnet wire for the secondary (450 turns wound on top of the primary). I found both these size wire in various solenoids and relays I’ve discombobulated. 🙂 Wire sizes aren’t critical but these are known to fit and the #40 can be handled with a reasonable chance of not breaking.
    • Sleeving to protect the primary wires where they leave transformer. I used approximately 2″ of insulation (each lead) from the individual wires in some 25 pair phone cable.
    • Wirewrap wire or other thin insulated wire to terminate the secondary wires where they leave the transformer.
    • Insulating tape. 1 mil Mylar or similar is desirable. However, I’ve found that thin clear (non-reinforced) packing tape does an adequate job, though it probably doesn’t have as much dielectric strength as real insulating tape so additional layers are required. It will also likely not stand up to overheating too well. Electrical tape is way too thick and would prevent enough turns from fitting.
    • A piece of Perf. board with holes on 0.1″ centers, 0.8″x0.8″. There should be 7 rows of holes each way so that one hole lines up in the center.
    • A Nylon 4-40 screw and nut to fasten the transformer to the board.
    • Four (4) machined-type IC socket pins or something similar to use as terminals.
  2. Wind the primary:
    • Slip a piece of sleeving over the start of the primary wire and position the sleeving so it extends about 1/2 turn inside the bobbin on the left side.
    • Wrap exactly 9 turns of this wire clockwise around the bobbin, left to right. The wires should enter and exit on the same angular position (slot) of the bobbin on opposite sides.
    • Slip another piece of sleeving over the wire end exiting the bobbin so that it too is about 1/2 turn inside the bobbin.
    • Wrap 1.5 to 2 turns of tape tightly over the primary winding to secure and insulate it.
  3. Wind the secondary:
    • Strip 1/8″ or so from the end of a 2″ piece of wire-wrap wire and solder the start of the wire for the secondary winding to it. Make sure the insulation on the fine magnet wire has been removed – usually just heating it while soldering will do this. Leave an inch or so of the magnet wire extending from the connection so that continuity can be confirmed with a multimeter, then snip it off. Install this in the opposite slot of the bobbin also on the left side with about 1/4″ of insulation inside the bobbin against the side and separated from the primary. Leave a little slack in the fine secondary wire so that slight motion won’t break it. Add a small piece of tape to protect and insulate this connection.
    • Using your coil winding machine (you do have one, correct?), build up the secondary in layers of about 50 to 75 turns in a counter-clockwise direction (bobbin being rotated clockwise). A single layer of wire won’t fit in the 1/8″ or so available (in the 18×11 mm core bobbin) so there will have to be some overlap. But, do this several times across the layer so that any given wire won’t be next to one with a much different voltage. In other words, wind a few turns and back up so that there will in essence be multiple sub-windings of 5 or 10 turns, repeated several times across the layer. Keep the wire at least 1/32″ away from either edge of the bobbin.
    • After each full layer or wire, add just over 1 layer of insulating tape making sure it covers the entire width of the bobbin. There should be just enough overlap to assure there is at least 1 layer of insulation but not much more as excessive tape will end up taking up too much space.The entire 450 turn winding will then require 6 to 9 full layers. Add another layer of insulating tape over the last winding layer leaving the wire end exposed.
    • Terminate the end of the secondary winding with another piece of thin wire by soldering as above. Confirm continuity with a multimeter. For the 450 turn secondary, the resistance should be about 60 ohms. Add a piece of thicker sleeving over this at the HV end if space is available. Else, use some bits of tape to insulate the wirewrap wire lead from the core and exposed inner layers that it may come near as it exits out the side of the bobbin. Add another layer of tape to secure the lead in place.
    • Add several more layers of insulating tape to complete the bobbin assembly.
  4. Prepare the mounting board:
    • Widen the center hole to 7/64″ to accommodate a 4-40 nylon screw.
    • Widen the holes at the 4 corners of the board to accept the 4 IC socket pins (if used) as a press-fit or glue them in place with 5 minute Epoxy or SuperGlue.
  5. Final assembly:
    • Install the ferrite pot core halves to the bobbin taking care not to crunch any of the wires. Orient it so that the primary and secondary leads are conveniently located with respect to the 4 pins, e.g., primary start: bottom left; primary end: top left, secondary start: bottom right; and primary end: top right.
    • Use the nylon 4-40 screw and nut to *gently* secure the transformer to the mounting board. The head of the 4-40 screw should be underneath the board. Don’t over-tighten or it may crack the core, especially if it has an air-gap in the middle.
    • Carefully remove the insulation from the ends of the wires. The secondary wires will still be fragile even with the wirewrap wire terminations. For the magnet wire, the easiest way to remove the insulation is to burn it off with a match or hot soldering iron and then clean with fine sandpaper.
    • Push the wires into their respective socket pins. (The wirewrap wires are too thin to be secure but they will make adequate contact for testing.)
    • Use a multimeter to confirm continuity of the primary (close to 0 ohms) and secondary (about 50 to 75 ohms).
  6. Testing:
    • Install the transformer in you HV Module. Attach a He-Ne laser tube and ballast resistor.
    • Power up on an variable DC power supply and check for reliable starting and stable operation. Adjust the core gap if needed. A smaller gap may result in more operating power available at a given input voltage. A larger gap will result in attempts to start on a lower input voltage. Somewhere around 0.005″ is probably a good compromise.
    • After testing the transformer (and adjusting the core gap if needed), use some adhesive to secure the pot core sections and to protect the transformer leads. Solder the leads into the socket pins.

The final result is shown on an adapter below:

Photo of SG-HM2 HVM2-1 Transformer being Tested in IC-HI1
Photo of SG-HM2 HVM2-1 Transformer being Tested in IC-HI1

The instructions for winding the HVM2-5 transformer are similar except for the dimensions, wire sizes and lengths, and number of turns for the primary and secondary:

  • Differences in parts list for T501 of HVM2-5 compared to T101 of HVM2-1:
    • 26×16 mm (2616) ferrite pot core with a small air-gap (no more than 0.005″) or no air-gap, and a single section bobbin.
    • Approximately 2.0 feet of #26 magnet wire for the primary (12 turns wound first) and approximately 75 to 120 feet of #40 magnet wire for the secondary (600 or 900 turns wound on top of the primary).
    • A piece of Perf. board with holes on 0.1″ centers, 1.0″x1.0″. There should be 9 rows of holes each way so that one hole lines up in the center.
    • A Nylon 10-32 screw and nut to fasten the transformer to the board.

Since the peak voltage on the HVM2-5 secondary may be 2 to 3 times higher than for HVM2-1, extra insulation and clearances will be required on the secondary.

SG-HM2 Printed Circuit Board Layout

A printed circuit board layout is also available. The Control Module is 2″x1.2″. The HV Modules are 3.6″x1.2″ and 4.5″x1.8″ for the 1 mW (HVM2-1) and 5 mW (HVM2-5), respectively. The Control and HV Modules are connected by a 2 pin cable for transformer drive and a 3 pin cable for current sensing from the laser tube. The two boards can easily be merged if desired.

The layout of the 3 PCBs may be viewed as a GIF file (draft quality) as below:

Sam's Modular He-Ne Laser Power Supply 2 PCB Layout
Sam’s Modular He-Ne Laser Power Supply 2 PCB Layout

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A complete PCB artwork package for SG-HM2 (all PCBs on one sheet) may be downloaded in standard (full resolution 1:1) Gerber PCB format (zipped) as [download id=”5612″]

The Gerber files include the component side copper, soldermask, and silkscreen; solder side copper and soldermask, and drill control artwork. The original printed circuit board CAD files and netlist (in Tango PCB format) are provided so that the circuit layout can be modified or imported to another system if desired. The text file ‘sghm2.doc’ (in sghm2grb.zip) describes the file contents in more detail.

Note: The netlist does NOT include wiring for the HVM2-5 HV Module. Also, part numbers on the HVM2-5 PCB actually begin with a “5” instead of a “1” since Tango PCB will not allow duplicate part numbers on the same layout.