Copyright Brian Brzezicki 2015
Sync Circuits
Often MC problems are due to the Sync circuit, here's the values and where they can be tested
| Horizontal Signals |
| Signal | Frequency | Test at chip and pin |
| 10Mhz | 10Mhz | d7 #9 |
| ! 10Mhz | 10Mhz | d7 #8 |
| 5Mhz | 5Mhz | d6 #10 |
| ! 5Mhz | 5Mhz | d6 #9 |
| 1H | 2.50mhz | d6 #6 |
| ! 1H | 2.50mhz | d6 #7 |
| 2H | 1.25mhz | d5 #14 |
| 4H | 6.25 khz | d5 #13 |
| 8H | 312.5 khz | d5 #12 |
| 16H | 156 khz | d5 #11 |
| d5 ripple | 156Khz | d5 #15 |
| 32H | 78khz | e5 #14 |
| 64H | 39khz | e5 #13 |
| 128H | 15khz | e5 #12 |
| H BLANK | 15khz | e5 #11 |
| ! HBLANK | 15.6khz | e7 #8 |
| HSYNC | 15.6Khz | a4 #14 |
| Vertical Signals |
| Signal | Frequency | Test at chip and pin |
| 1V | 7.8khz | a4 #3 |
| 2V | 3.9khz | a4 #2 |
| 4V | 1.95khz | a4 #6 |
| 8V | 976hz | a4 #7 |
| 16V | 488hz | b4 #3 |
| ! 16V | 488hz | d3 #10 |
| 32V | 244hz | b4 #2 |
| 64V | 122hz | b4 #6 |
| 128V | 61hz | b4 #7 |
DRAM write controller @ L6
This is and Atari labeled bi-polar PROM, it is often socketed, if it is REPLACE THE SOCKET. I hate arbitrarily replacing anything, but this socket is usually bad and often causes a lot of weird issues. Take the 30 seconds to replace it and save yourself alot of headaches.