Guess based on other displays and the PCB markings:

Segments A-G might follow the layout here: https://upload.wikimedia.org/wikipedia/common … ed_Segments.svg

3 rows, one for each number.

Jumper from Letter to 1 (low), 2 (high), 3 (low+high). So the letter is like pivot that you rotate the jumper around depending on when you want that segment to light up.

The rows do not always follow the same orientation but can also occur 'flipped' vertically.

PARKE wrote on 2021-12-20, 13:21:

The rows do not always follow the same orientation but can also occur 'flipped' vertically.

True, but you can just see the 'G' silkscreen mark for the bottom row, so I think that tells you that row's 'T' arrangement, and the other rows can be seen more easily. Plus I think it fits with what can be seen of the PCB traces on the other side.

At the moment, if I'm right, then there's a jumper on the top row between C3 and B1, which I think means that any LED that should only be on when Low is selected (like top row G) will always be on. My guess is that the display is stuck on 200.

That is actually the jumper that made me think about the orientation. If the orientation of the left top row is like the red lines indicate then that jumper should be at the bottom I think ?

I think that's going to depend on what number is wanted. At the moment (again, if I've got this right) then if the top row 'C' jumper was moved down, so it connects to C1, then the display would then switch between (assuming top row is the hundreds):

1 _   _   _          _   _   _ 
2 _| | | | |  and     | | | | |
3|_| |_| |_|        |_  |_| |_|

neither of which look right. Let's wait and see if any of this matches what the display actually does. Or if anyone does have the actual manual.

Yeah, the current jumper setting makes little sense. It's a bit like a chinese puzzle and the same impression I get from those 'manuals'. The simplest way to check how it works is imo via connecting it to a battery and play with the jumpers.

Thanks. Yes, the current jumper configuration is set to say 200 on both turbo and non-turbo mode. I'm going to adjust it to read 75/25.

feipoa wrote on 2021-12-20, 20:47:

Thanks. Yes, the current jumper configuration is set to say 200 on both turbo and non-turbo mode. I'm going to adjust it to read 75/25.

Do you know the value of that resistor? With just the one resistor it means that the current through each LED will vary with the number of LEDs lit up. As fewer are turned on the current on the remaining ones goes up. Too few lit up (75 only use 8 segments) might lead to LEDs burning out. If you're just using two of the digits then you might want to increase the resistance a bit.

Might not be an actual problem.

Should be 42-ohms based on the colour code.

Probably something like a 2V forward voltage drop over an LED, leaving 3V over the resistor. At 42 ohms, that give 3/42 ~= 70mA through the resistor, shared between LEDs. Max current per segment probably around 20mA. So as long as 4 are lit then it should be ok. Not a problem then, if I've got that right. Unless you decide to run something at 11MHz. Might start to get a bit dim running at 888MHz.