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Quote from: TK on September 25, , pm This thread is old but I think it is worth keeping any repair hints together. Recently I acquired this signal generator and had missing columns on the bottom half of the LCD.
After replacing the LCD, the problem persisted. While trying to map the LCD pins to the correct part on the motherboard, I used a continuity meter to map the pins. I then realized that the motherboard has a 3V lithium battery to keep some configuration alive and I passed the test probes over pins while they were powered by the Battery.
After soldering new SRAM chips, the motherboard booted correctly passing all the self diagnostics. There were some more problems, most of them were easy to fix. One switching voltage regulator was shortet, and two transistors display and green power LED were shot.
But the lines in the display were still there. After analyzing the protocol of the data transfer to the display, I was short before taking my logic analyzer. I even replaced the RAM chip a second time. But then I did some testing with removing signals to the display, and pulling the 8 lines to H one at a time. No result on bit 8. Problem was a bent contact in the connector of the board to the LCD display! Looking back, it was obvious, because there came no signal for these lines out of the board.
With black screen, alll signals were constant L. Pulling one of the 8 bits H there were white lines. But not on bit 8. It just had no contact to the display. But I was also sure that the problem came from the display controller or a bad display RAM chip. Key to the solution was to understand the display transfer protocol, which explained whyonly the lower half of the display was faulty. I am glad you found the problem with the board and the display is now working.
Thanks for the follow up.
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