Electronics > Repair

Looking for Mettler Scale ROM backup

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PA0PBZ:

--- Quote from: gmac34 on October 30, 2024, 01:46:55 pm ---Non having a schematics is bummer, but one last thing that comes to mind is to check the IC1, the PC74HC373P. but I don't fully understand what is it doing there, by the position it would seem like it would interface between the ROM and the micro.

--- End quote ---

The lower 8 address lines and the data lines are on the same processor pins, so they need to be 'demultiplexed' and latched. See reply #31 in this thread.

jamarjan:
I connected the logic analyzer to the 373 latch
below is a screenshot with the channel descriptions
unfortunately I don't really know how to interpret it

gmac34:
I cannot help you with that, but I have one last thing I think you should check: I would check the data input on the vfd controllers, should be pin 39, to see if they are receiving any data. A bad controller might be another explanation for a blank screen

https://www.digchip.com/datasheets/parts/datasheet/477/SN75518N-pdf.php

jamarjan:
Thanks for the suggestions!
Actually, the diagnosis after repairing the power supply and restoring stable voltages at the control points I just started with the VFD controllers
Unfortunately there is no data reaching the display board (voltages are ok)
The only life I get on the display board is if I run the scale without the cassette. Then all segments light up. I can turn the display off and on by pressing the spacebar button.

It seems to me that driving the display is secondary to loading data from the EEPROM. And here, unfortunately, I have no information exchange between the uC and the memory.

gmac34:
I see, well, for what is worth the display lighting up with no cassette is normal behaviour

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