Ma9006
3.1.6.3. Storage unit
3.1.6.3.1. General information
The storage circuit, located on the storage unit, supplies voltage levels and timing pulses to control the storage part of the C.R.T. in the SAVE, READ, ERASE and WRITE modes and in the positions PERSISTENCE and MAX. WRITE.
The storage circuit will be discussed with the aid of the simplified diagram of this circuit as shown in Fig. 3.12. The schematic of this circuit is on the diagram Fig. 3.51. at the rear of the manual.
The WRITE mode is operative after depressing push-button SK25.
Assume that as a result of an ERASE control signal the storage layer (g9) is at a potential below the cut-off level (Fig. 2.9. and 3.10.) and no flood-gun electrons reach the screen. We now activate the writing gun and let the electron beam move over the storage layer surface. Due to the high potential difference between the writing cathode and the storage mesh (approx. 1500 V), the electrons arrive at the storage layer with such an energy (velocity) that secundary emission occurs. Wherever the surface is struck by the electrons, a positive charge will arise. The highest potential that can be attained in this way is +32 V (see Fig. 3.9.) in relation to earth (approx. same potential as the flood gun cathode). At any value above this potential, the flood-gun electrons would be attracted by the storage-layer surface, thus reducing its potential to the original +32 V value. Those areas of the storage-layer surface that have been charged to near +32 V in relation to earth, allow the post-accelerator field to 'reach through' and capture flood-gun electrons. Thus, the pattern of charge on the storage-layer surface is displayed on the screen.
In the WRITE mode, potentiometer PERSISTENCE may be used to vary display persistence from less than 0,3 sec to more than 1,5 min. This persistence control is attained by using a series of square-wave pulses (Fig. 3.10.) in order to periodically "wipe" the writter signal from the storage layer.
These erasure pulses are obtained by comparing (I.C. 1001 4.5.13.) a 2 kHz triangular voltage with the variable d.c. voltage of PERSISTENCE potentiometer R10.
For explanation of the diagrams are 3.1.6.7. "Erasure in the write mode".
The potential of the flood-gun accelerators g'2 and g"2 depends on the selected operating mode (see Fig. 3.8. and oscillogram 19 in the circuit diagram). In the MEMORY OFF (SAVE and READ push-buttons operated simultaneously) and WRITE modes, transistor TS1019 is hard on and the potential of the flood-gun accelerators is continuously +80 V in relation to earth.
- Potential
Fig. 3.8. Flood gun accelerators potential during storage mode
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