Patent GB-1275093-A (GB)
Title: Improvements in or relating to television equipments
Inventor: HEIGHTMAN ANTHONY NORMAN
IPC: H04N5/222
Filed: 1969-08-07
Abstract: 1275093 Television camera testing MARCONI CO Ltd 26 May 1970 [7 Aug 1969] 39588/69 Heading H4F A television camera (especially a three tube colour camera) and auxiliary equipment is broken down for analysis purposes into a plurality of sub-units and the good or bad condition of each sub-unit is monitored and displayed on a respective section of the display area of a monitor display tube, appropriate test signals being fed to each sub-unit during the intervals that the respective section is being scanned. A typical breakdown for a colour camera is 9 sub-units in the camera unit (3 per tube), 3 sub-units in the camera cable (1 per tube) 12 sub-units in the camera control unit (4 per tube) and 8 sub-units in the power supply. Fig. 1 shows the breakdown for the green channel comprising pick-up tube A1, video amplifier A2 and video processor A3 in the camera unit (CAM) the single cable sub-unit A4, and sub-units A5, A6, A7 and A8 in the camera control unit (CCU). The monitor display tube is divided, possibly with the aid of a physically superimposed referenced grid, as shown in Fig. 2, the columns 1 to 8 denoting the sub-unit number, and the rows A to D denoting the green, red and blue channels and the power supply. To monitor the camera &c., three poled-two way switch SU is moved from the normal position as shown to the lower position. In this position a blanking pulse BS2 is applied via S1 to blank-off the pick-up tube A1. To monitor the pick-up tube A1, generator PG1 produces a pulse A1, Fig. 2 lasting for the first <SP>1</SP>/ 8 th of all of the first quarter of the television scan lines. These override pulse BS2 and switchon the tube A1. Section A1 of the monitor display thus shows a part of the viewed scene. To monitor the sub-unit A2, generator PG1 produces pulse A2 for feeding, via an isolating resistor, to the unit and occurring during the same lines as pulse A1 but delayed <SP>1</SP>/ 8 th line therefrom. If unit A2 is good, the display section A2 brightens up. If A2 is bad, sections A1 and A2 both remain dark. Pulses A3 and A4 similarly are sent to and test sub-units A3 and A4. Pulses A5, A6, A7 and A8 are generated at PG2 and respectively test the camera control unit. The sub-units B1-B8 and C1-C8 of the red and blue channels are similarly monitored by pulses from the generators PG1 and PG2, the pulses occurring during the second quarter and third quarter respectively of the line scans. Signals SD1, DS2 ... SD8 from the power supply sub-units are tested with respective reference signals in comparators VC1, VC2... VC8. Any detected inequality (fault), gates through an appropriate signal for the last quarter of the line scans so that a section of row D in the monitor indicates the faulty sub-unit. The signals A, B, C, from the channels and those ND1-ND8 from the power supply section, are combined at CSC for passage via 52 to the monitor PM. If the monitor is a colour receiver a colour subcarrier may be added to the pulses to give distinctive coloured sections. The pulses may be intermittant to give flashing sections.