Products > Test Equipment
Replacing OLED screen on an Agilent U1253A Multimeter
LagrangeWang:
do you have a PCB file ,and i want to know why your solution doesn't have a coulum offset
gmarsh:
I just pulled a U1253A out of the junk bin at work with a dead screen, that I'm gonna have a go at fixing.
I'm curious if I can fix the column offset issue, perhaps using a CPLD to offset the column address when it gets written in. If I'm lucky, the meter writes only full rows at a time starting at the same column address, and all I have to do is substitute the column address for another.
I'll be stuffing my MSO on the display header shortly to take some captures of the meter writing to the screen, and figure out how feasible this is. Updates to follow...
gmarsh:
Update!
I hooked up the MSO to the meter and did some captures. Some observations:
- The meter doesn't seem to care that there's no LCD plugged in, and doesn't seem to ever read from the display.
- The meter doesn't write full pages at a time from the same starting column offset, it writes randomly to the screen.
- But... every time the meter writes to the display, it always writes the page first (0xB#), then the column LSB (0x0#), then the column MSB (1x#)
This means we can add a value to the column LSB command when it's written to the screen, catch the carry bit and add it when the column MSB command is written to the screen. This is an easy CPLD job.
I've attached some Verilog that implements this and also flips the bit to reverse the display. It's pretty simple and uses only 19/40 logic elements in a <$2 Intel 5M40E64 "MAX V" CPLD, which you can program with a ~$2 USB Bus Blaster clone. Right now I've got the column address offset set to +2 as a placeholder, which is probably wrong, but it's something I'll mess with once I get hardware in my hands.
Just ordered a OLED screen off aliexpress, and I'm gonna start throwing together a schematic.
I ordered a 31 pin solder-on screen that's the same style as the old screen, but I should measure and find out if a flat connector screen can be made to fit too.
TestSubject:
I am excited to hear some updates gmarsh! For some reason, my U1273a got real dim with missing pixels after being shipped across the pacific...
Which display did you end up buying? If you need help with PCB design and/or testing, I am happy to oblige!
gmarsh:
--- Quote from: TestSubject on February 01, 2021, 04:55:30 am ---I am excited to hear some updates gmarsh! For some reason, my U1273a got real dim with missing pixels after being shipped across the pacific...
Which display did you end up buying? If you need help with PCB design and/or testing, I am happy to oblige!
--- End quote ---
Time for another update I guess:
- I sniffed the screen activity some more, to get a full idea of what the meter writes to the display.
- The lowest column address value sent to the screen is 0x02, which causes the column shift everyone is seeing. So all we need to do is subtract 2 when an address is written to the screen and that should center everything properly, and since the address is sent LSB-first from meter to screen (on the 1253A, at least) we can do that.
- The Verilog I posted earlier will wreck some command arguments that are sent to the screen on startup, so don't use it :) I've got newer CPLD code now which looks for commands that take an argument and passes through the argument unmodified, and still fits in a 5M40ZE64 CPLD with ~60% utilization. I'll probably throw down a 5M80 for the first prototype run in case I run into any surprises.
- And I've got a new PCB designed, which I'll be ordering in the next week or so.
I'm also laying out a tester PCB that a display plugs into so I can measure all the rail voltages, program the CPLD and show a test screen on the OLED without having to use a real (and expensive) meter as a host. I'm also finishing a couple other projects to make one big JLCPCB order (+ one big Digikey order) at once.
I ended up ordering this screen afterwards:
https://www.aliexpress.com/item/4000321242073.html
I don't need any help with the PCB design, but my big question is whether what I'm doing here for the U1253A can drop into your U1273A. Any chance you've got a 4 channel scope or MSO or anything that can capture what gets written from the meter to the display?
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