Hitachi Monitor
 

I had problems with a Hitachi monitor in that the video would randomly disappear. After some moving of the BNC input I concluded that there was a dry joint on the BNC to PCB. So off with the cover and removal of the ‘offending’ pcb. Sure enough the BNC locking nut was loose so duly tightened. It was put back together and same problem. Move the BNC and the picture came and went. Time for more investigation. With covers off and the monitor giving a picture I moved the BNC and the picture went away. This was very repeatable, flex the input board and the picture would come and go. I took out the input board and gave it a close inspection under a magnifier all the joints looked OK. (photo input and sub board)
I noticed that the input board was held to another daughter board by some plastic standoffs and that as the input board was flexed this board also moved. So with a picture displayed I moved the daughter board and lo and behold the picture came and went. It looked like this board was connected by plug and socket but further investigation showed that it was soldered directly to the motherboard.(photo sub board) To gain access to the underside of the motherboard I had to slide it out from the chassis and undo several multiway connectors. With the main board out and access to the underside I had a close look at the joints. There was nothing really visibly wrong with any of them but I resoldered them all. It was impossible to test the monitor with the main board out as too many connectors had been disconnected, so I rebuilt it and powered it up. Result. Flexing the input board no longer caused to picture to come and go. It was cased up and left on soak test for several hours with the occasional moving of the BNC input, no loss of picture.(photo testcard)

Malcolm