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Sony Watchman FD-20 Flat CRT TV Teardown

Sony Watchman FD-20
Sony Watchman FD-20

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.

Front Panel
Front Panel

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.

Back Panel
Back Panel

The back panel has the battery compartment & the tilt stand.

Certification
Certification

The certification label reveals this unit was manufactured in May 1984, 32 years ago!

Spec. Label
Spec. Label

Rated at 6v, ~2.1W this device uses surprisingly little power for something CRT based.

Battery Holder
Battery Holder

The battery holder is a little unique, this plastic frame holds 4 AA cells, for a 6v pack.

Battery Compartment
Battery Compartment

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.

Front Panel Removed
Front Panel Removed

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.

Back Cover Removed
Back Cover Removed

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.

CRT Electron Gun & Flyback Transformer
CRT Electron Gun & Flyback Transformer

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.

CRT Rear
CRT Rear

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.

Sony 02-JM Flat CRT
Sony 02-JM Flat CRT

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.

HV Module
HV Module

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.

Bare CRT
Bare CRT

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.

Electron Gun
Electron Gun

The electron gun in the neck looks to be pretty much standard, with all the usual electrodes.

Viewing Window
Viewing Window

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.

FD-20 Schematic
FD-20 Schematic

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!