you are here clock

This is a Radar Scope CLK board (click on the picture to enlarge - 127 KB).

Several of the heat fins on the ECL chips are missing and one of the ECL RAMS is even ripped open, exposing the die but - amazingly - this board is still working!

If you need to identify an unknown board you can view this full sized CLK board image (size is 410 KB)

The CLK board provides basic timing functions:

it generates the system clock (derived from the 73.728 MHz crystal at A6)
it generates sync and blanking signals for the video output
it holds the two line buffers for the horizontal output (2 x 256 pixels)
line buffer1 is located at 5L and 5M (ECL RAM type MB7072) see schematic on video page
line buffer2 is located at 5N and 5P (ECL RAM type MB7072)

Signal on test point TP2, top middle of the board. Scope x=0.2 V/div; y=50µs.
This is the B1SL signal which provides switching between text and video RAM.

Oscillator and system clock signal

The oscillator circuit is shielded under a small sheet brass box at the lower left of the CLK board. The primary clock signal emerges at test point TP1 which is connected to the small ferrite coil marked "T1".
Then it is connected to a 10116 ECL triple line receiver which is used to adapt and buffer to the following two 10135 ECL dual J-K master slave flip-flops (position 6F). These two FF's divide the primary clock signal by 3, this signal (Ø3) appears at 6F, pin 14 and is at (73.728 / 3 = 24.576 MHz).

Ø3 clock signal at 6F, pin 14 (left side of ECL pull down resistor R18)

The 1H signal (3.072 MHz) is going to the video board via connector P2-CLK, pin 46. There it is buffered and named 1HB. It leaves the video board on connector P4-CPU, pin 5 and goes to the cpu board where it is buffered again and finally becomes the clock for the Z80A on its pin 6.

Signal Name Frequency

¼H 12.288 MHz

½H 6.144 MHz

1H 3.072 MHz

2H 1.536 MHz

4H 768 kHz

8H 384 kHz

16H 192 kHz

32H 96 kHz

64H 48 kHz

128H 24 kHz

256H 12 kHz

CLK power input

This is the upper left edge of a TRS2-03-CLK board, showing POWER IN (left) and OUT (on the right) connectors. See also in the power supply section.