I've recently had a problem with a MY41XXXXXX serial# unit with the VFD which wasn't related to a leaky driver or bad segments. See image.
All characters that used any top 3 middle segments "\|/" were corrupted. These are SEG_I, SEG_K and SEG_L, not identified in any order.
In the process I could not find any reference for U606 VFD SEG_XX pin mapping to display segments. The 18 segment signals (SEG_B, SEG_C, SEG_D, SEG_E, SEG_F, SEG_G, SEG_H, SEG_I, SEG_J, SEG_K, SEG_L, SEG_M, SEG_N, SEG_O, SEG_Q, SEG_DP1, SEG_DP2, SEG_COM) will map to each element of a given GRID. The "4W, diode and buzz" annunciators I expect replace the two dots and comma for the right end digit, where these are redundant. Each digit also has its own annunciator which I expect is one of the SEG_XX lines.
Attached are a few findings which are related to this fix which ended up being debris under IC U603, the VFD driver, specifically around pins 34/35/36. These pins were clearly shorted on the VFD side when testing with a meter, cutting one of the VFD pins isolated this to a driver side issue. On reflection there is enough space around the VFD PCB holes to extract the solder and isolate the pin from the PCB.
When I find some time I will reverse engineer the full segment mapping.