Topic: Dragon Breed M72 Repair help needed  (Read 2530 times)

Author Message

0 Members and 1 Guest are viewing this topic.

Offline Lota

  • ZX80
  • *
  • Posts: 5
  • Kudos 1
  • Gender: Male
    • View Profile
Dragon Breed M72 Repair help needed
« on: May 12, 2013, 06:22:37 PM »
Hi Everybody,

Last week my frend visited me and brought a broken M72 Dragon Breed board to my and requested to repair that.
He said originaly the "C" board was built with more different eproms, but those and the security chip were totally rusty and many of the legs broke down when he removed the chips. His frend sent new chipset and the jumpers was modified based on new configuration. He started the board and on the screen was only some crazy color.

I started the repair with rams and I have found 3pcs broken what I exchanged. One of then is on the B boad and 2 of them on A board. No any changes. So I meassured around the CPU and I have found that the reset pin is permanently high. So I checked the way of reset signal and finaly found that IC 51 74ls138 is broken. I exchanged it. The CPU started to give out signals. I also found 3 chips by oscilloscope, what ware broken IC62 74ls32, IC44 74ls373 and IC77 74ls158.
On the screen almost everything are the same as the beggining. I have schematic for R-Type what is almost the same, but I don't have any idea what sould I check, what cause the problem.

I attach some pictures about the screen and about boards.

If anybody has any idea what can be the root cause of problem or how can I repair it don't hesitate to write me.

Thanks a lot!

« Last Edit: May 12, 2013, 07:51:02 PM by Lota »