one of the segments of my DISMO doesn’t work
(the top bar on the right side digit)
can it be replaced ? Or removed to check dry soldering?
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one of the segments of my DISMO doesn’t work
(the top bar on the right side digit)
can it be replaced ? Or removed to check dry soldering?
i should mention it’s the original small dismo
It doesn't necessarily have to be a defective LED display, but might as well be a bad solder joint on one of the resistor packs, or a bad output pin on the MCU. Do you have a high-resolution camera with Macro setting? Some mobile phone cameras really produce good pictures these days, and the 4x0402 resistor packs aren't that small. Let's try a visual inspection from a distance
which area of board do u want?
IPhone 12 camera…should be ok?
The DisMo is pretty small - and the "small" version has all components exposed. These are the interesting ones.
Not sure about iPhone camera - heard a lot of good things, but I don't use Apple stuff. I like turning rings on a real lens and hearing the mirror flip up. Call me retro
hopefully that’s ok?
Sorry I can’t go old school for it
The segment in question goes through RN4, 3rd resistor from the PCB edge. I don't see an obvious problem in your pic, but the picture isn't really sharp there, looks like the camera tried to make "nice surfaces". Maybe a different angle reveals more? Or just add some flux, heat up the solder spot and see if it makes a difference.
gave RN4 a reflow...still the same no change
i can use my oscilloscope if you want me to look at anything specifically or a logic probe
If you measure voltage on the 3rd pin fromt he DisMo edge and find that it's well above zero (7-segmant displays have common ground), you know that the 7-segment display has a fault.
Note that the brightness of the 7-segment display is controlled with pulse width modulation. A multimeter might show wild jumps, so an oscilloscope might really be the better choice.
3 pin on RN4 ??
which one if below is layout? pin 3?
5 4
6 3
7 2
8 1
<Edge of Board>
You should look at both pins that are "3rd from edge", so Pins 3 and 6 in your sketch.
scope shows all pins have similar output, and move as expected as display changes
however I can report that after poking around with the scope on the pins, the DISMO started working!,!..so maybe something shorting the pins?
anyway working now, so thanks…
although possibly the segment isn’t as bright as the other ones…
You can also "software-poke" around in the DisMo registers to turn single segments on/off and intermediate brightness (if you have a little software knowledge). See this part of the register documentation. Top segment of the right digit would be address $d8.da01. If you make a byte-write of $0f to that location, the segment should light up in full brightness. Lower brightness will be done with pulse width modulation, which is a lot harder to measure (and will result in flickering on any attempt to record it on video), so that probably won't help in identifying where the problem is (MCU, resistor, trace or display itself).
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