home

cpu
cpu

troubleshooting
troubleshooting

clock
clock

eproms
eproms

video / ess
video / ess

sound and voice
sound and voice

contact
contact

power supply
power supply

links
links

you are hereclock


CPU_TRS2_03 full view

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)
TP2 on clock board

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).

 

system clock signal Ø3 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