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.
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.
Here’s the supply on test, I’ve got the scope probes connected to the gate resistors of the drive MOSFETs.
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.
At maximum power on 12v input, about 25mm of gap is possible with an arc.
Here’s another Sony Flat CRT TV, the FD0280. This one was apparently the last to use CRT technology, later devices were LCD based. This one certainly doesn’t feel as well made as the last one, with no metal parts at all in the frame, just moulded plastic.
Being a later model, this one has a much larger screen.
Instead of the manual tuner of the last Watchman, this one has automatic tuning control, to find the local stations.
The spec puts the power consumption a little higher than the older TV, this isn’t surprising as the CRT screen is bigger & will require higher voltages on the electrodes.
The certification label dates this model to May 1992.
Still not much in the way of inputs on this TV. There’s an external power input, external antenna input & a headphone jack. No composite from the factory. (Hack incoming ;)).
The UHF/VHF & power switches are on the top of this model.
Removing some very tiny screws allows the back to be removed. There’s significant difference in this model to the last, more of the electronics are integrated into ICs, nearly everything is SMD.
There’s the usual RF tuner section & IF, in this case the VIF/SIF is a Mitsubishi M51348AFP.
The digital control of the tuner is perfomed by this Panasonic AN5707NS.
The deflection & sync functions appear to be controlled by a single Sony branded custom IC, the CX20157. Similar to many other custom Sony ICs, a datasheet for this wasn’t forthcoming.
There’s very little on the top side of the board, the RF section is on the left, there’s a DC-DC converter bottom centre next to the battery contacts. This DC-DC converter has a very unusual inductor, completely encased in a metal can. This is probably done to prevent the magnetic field from interfering with the CRT.
Here’s the CRT itself, the Sony 03-JM. The back of this CRT is uncoated at the bottom, the tuning scale was taped to the back so it lined up with the tuning bar displayed on the screen.
Here’s the electronics completely removed from the shell. There’s much more integration in this model, everything is on a single PCB.
The curve in the phosphor screen can clearly be seen here. This CRT seems to have been cost-reduced as well, with the rough edges on the glass components having been left unfinished.
Here’s the electron gun end of the tube. There isn’t a separate final anode connection to the bell of the tube unlike the previous model. Instead the final anode voltage is on a pin of the electron gun itself. This keeps all the wiring to the tube at one end & shortens the high voltage cable.
Here’s the gun in the neck of the tube. Again this is pretty much standard fare for CRT guns. It’s more similar to a viewfinder tube in that the anode connection is running from the pins at the back. (It’s the line running up the right side of the tube). I’m guessing the anode voltage is pretty low for this to work without the HV flashing over, probably in the 2-4kV range.
Here’s an oddity from the 1980’s – a CRT-based portable TV, with a very strangely shaped tube. Sony produced many types of flat CRTs back in the 80’s, with the electron gun at 90° to the curved phosphor screen.
The front panel has the display window, along with the tuning & volume indicators. Unfortunately since analogue TV transmissions have long been switched off, this unit no longer picks up any transmissions off the air, but it can be modified to accept a composite video input.
The back panel has the battery compartment & the tilt stand.
The certification label reveals this unit was manufactured in May 1984, 32 years ago!
Rated at 6v, ~2.1W this device uses surprisingly little power for something CRT based.
The battery holder is a little unique, this plastic frame holds 4 AA cells, for a 6v pack.
The battery holder slots into the back of the TV, there’s also an extra contact that the service manual mentions is for charging, so I assume a rechargeable 6v battery pack was also available.
Removing a pair of pin-spanner type screws allows the front glass & screen printed CRT surround to be removed. Not much more under here other than the pair of screws that retain the CRT in the front frame.
Here’s the back cover removed, after unscrewing some very small screws. As per usual with Sony gear, the electronics is extremely compacted, using many flat flex cables between the various PCBs. The main PCB is visible at the back, this has all the deflection circuitry, RF tuner, Video IF, Audio IF, video amplifier & composite circuitry.
Lifting up the main board reveals more PCBs – the high voltage section for the CRT with the flyback transformer, focus & brightness controls is on the left. The loudspeaker PCB is below this. The CRT electron gun is tucked in behind the flyback transformer, it’s socket being connected to the rest of the circuitry with a flat flex cable.
Here’s the back of the CRT, the phosphor screen is on the other side of the curved glass back. These tubes must require some additional deflection complexity, as the geometry will change as the beam scans across the screen. There’s a dynamic focus circuit on the schematics, along with extensive keystone adjustments.
Here’s the tube entirely extracted from the chassis. The EHT connection to the final anode is on the side of the tube bell, the curved phosphor screen is clearly visible. The one thing I can’t find in this CRT is a getter spot, so Sony may have a way of getting a pure enough vacuum that one isn’t required.
I’d expect the vertical deflection waveforms to be vastly different on this kind of CRT, due to the strange screen setup. Not much of a beam movement is required to move the spot from the top to the bottom of the screen.
No doubt to keep the isolation gaps large, all the high voltages are kept on a separate small PCB with the flyback transformer. This board generates the voltages for the electron gun filament, focus grid & the bias to set the beam current (brightness) as well.
Here the deflection yoke has been removed from the CRT, showing the very odd shape better. These tubes are constructed of 3 pieces of glass, the bell with electron gun, back glass with phosphor screen & front viewing window glass. All these components are joined with glass frit.
The electron gun in the neck looks to be pretty much standard, with all the usual electrodes.
Here’s a view from the very top of the CRT, the curve in the screen is very obvious here. The electron beam emerges from the bell at the back.
Here’s the full schematic of the entire TV, I extracted this from a service manual I managed to find online.
More to come on hacking this unit to accept a standard composite video input, from something such as a Raspberry Pi!