Because one "Pentagon-128k" I all ready soldered and it is working :) Xobbiman brings to repair his own "Pentagon 128k":
1) Desoldering all cables from the board. Washing the plate with water and dry well:
2) Soldering plugs, so we can connect "Pentagon-128k " to SCART (RGB video):
3) Have video, but the image is unstable. Heat up some chips. Cuts the suspect chips. The same time change keyboard microchips (LS244). Soldering on the power bus ceramic capacitors. Now image is ok (the box with a black border):
4) Quadrate trash :(, it means bad ram memory. Cutting data tracks. Change ram chips. The image is becoming similar to what must be:
5) Bad ram chips :( in consultation with Xobbiman, I get permission to change all the ram chips. Cutting chip legs. Desoldering chips foots one by one. Cleaning holes. Soldering new ic sockets. The change proved successful, video image is a chess board:
6) Changing the Z80, VG93 and ROM sockets. Soldering some cutted chips. Put Z80, the picture remains the same, still a chess board. Ah, it means there is more another faulty chip or broken track:
7) Checking CPU signals: clock, reset, data and address lines. It looks like everything is okay. There is still a chess board :(
8) Change latch and small logics chips. Now have vertical lines:
9) Testing with ROM. Basic appears:
10) Soldering remaining chips. Trying TR-DOS commands. Drives head rush on the last track. Then there is the trouble with the main menu and tr-dos controller:
11) A series of chip replacement and "Pentagon-128k" fixed:
