Another Viewfinder CRT

Here’s another viewfinder CRT, removed from a 1980’s vintage VHS camera I managed to get cheap from eBay.

This unit is very similar to the last one I posted about, although there are a few small differences in the control circuitry.

Viewfinder Schematic
Viewfinder Schematic – Click to Embiggen

Here’s the schematic, showing all the functional blocks of the viewfinder circuitry. An integrated viewfinder IC is used, which generates all the required scan waveforms for the CRT.
On the left is the input connector, with the power & video signals. Only pins 2 (GND), 3 (Composite video), & 4 (+8v) are needed here. Pin 1 outputs a horizontal sync signal for use elsewhere in the camera, while pin 5 fed the recording indicator LED.

To make connection easier,  I have rearranged the wires in the input connector to a more understandable colour scheme:

Input Connector
Input Connector

Red & Blue for power input, & a coax for the video. For the video GND connection, I have repurposed the Rec. LED input pin, putting a shorting link across where the LED would go to create a link to signal ground. Keeping this separate from the power GND connection reduces noise on the CRT.

Viewfinder CRT Assembly
Viewfinder CRT Assembly

Here’s the complete assembly liberated from it’s plastic enclosure.

PCB Closeup
PCB Closeup

Closeup of the control PCB. The 3 potentiometers control the CRT brightness, focus & vertical size.

M01KGG007WB CRT
M01KGG007WB CRT

The tiny CRT. Only ~60mm in length, with an 18mm screen size. This tube runs on +2294v final anode voltage. Much higher than I expected.

Electron Gun Closeup
Electron Gun Closeup

The electron gun assembly, with the cathode, focus & final anode cups.

Phosphor Screen
Phosphor Screen

This screen is just a little bigger than a UK 5p piece! A marvel of precision engineering.

 

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