Electronics > Repair

Agilent/HP 34401A VFD bad Segments.

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naimns:
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.

Swake:

--- Quote ---In the process I could not find any reference for U606 VFD SEG_XX pin mapping to display segments.
--- End quote ---

In the service manual dated October 2005 there seems to be a pin to segment mapping. What I read for example is that SEG_B maps to pin 30 and is named Anode 16. Is this what you're looking for ?

naimns:
Thanks, Thats where I found the names of the segments from.
What would be useful is knowing which segment (SEG_XX) pin maps to which segment of the display. There are 14 segments on each alpha and then the 4 other for each GRID, so the 18 segments on the VFD pinout. This will help to identify which driver or VFD pin to observe.
I am hoping to short some pins and check which corresponds to which on the display. I've not found that information anywhere and I do not expect the names to follow a standard.

Swake:
ho, I see now.
And changes are they are not following standard protocol starting above left with the 'first' segment.

This might be of interest for you: Someone made a converter to allow for the connection of other display types in the 34401A: https://github.com/ragges/hp_display

naimns:
Yes, I did see that.
Most of those solutions are intercepting the messages that interact with U602 the 87C51 u-controller, so no information on how the U603 driver outputs map to the 18 segments.
Its Sunday tomorrow and this is bugging me so I may have to unpack my soldering iron.

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