One segment of the display GCP less bright

[Rico Coolen]

Hi all I am new to this forum and I have the following question. I can buy a GCP second-hand, but now I see that the 2nd segment of the display is less sharp. Still easy to read, but it is noticeable that it is less bright.
Is this a common problem, and is it easy to solve without incurring high costs? I am electrically skilled myself so I can do repairs myself. I would like to hear any findings before I might buy the unit.
I am now working on an "old" GC with V1.0 software. And I would like to upgrade.

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[JohnClark]

The display on the Ground Control Pro is actually scrolling/flashing at a high enough frequency that the human eye doesn't necessarily catch but a camera might... are you sure that photo is showing a reality?

Alternatively, if it is actually happening then the problem is unlikely to be the display itself but something else within the circuit that is causing it. Do all the button LEDs work correctly?

[Rico Coolen]

At first I also thought that it was the frequency that we cannot see with the eye, but a camera does. However, the seller says that it is visible in real life. He says he hadn't noticed before.
The question concerns the LEDs of the foot switches I just sent it.
Unfortunately the distance is too far so I can't see or test it at the moment.

Is the control of the display of a GCP the same as the "old" GC? Because I have one here, and I see that there are 2 ULN2003 that control all segments. But if it were broken, it would have to apply to multiple segments right?

[Rico Coolen]

I received an answer: All the LEDs of the foot switches are functional. The second segment is the only one that is less bright. All others are good.

Edit:
I took the gamble anyway and bought the GCP. If all goes well, it will be shipped tomorrow. When I have it in I can analyze it better and come back to it. Hopefully we will get it resolved

[Rico Coolen]

Okay, I got the unit in.
A number of things that immediately strike me:

-As said, the second digit burns less brightly than the other digits.
-The LED at foot switch 2 also burns less brightly than all other LEDs.
-When I press the 2nd foot switch, so that this LED lights up, I see the 2 digit dimming very minimally. It cannot be recorded on the camera. But it strikes me.
-In addition, I notice that the frequency with which the display switches is clearly more visible than with my old Ground Control unit.
This cannot be seen with the naked eye on my old unit. When I try to film this it is visible on both units.

The control of the display is provided with a number of uln2003 with a number of 74hct374 flip flops.
So this is very similar to the same control as the old unit.
Because the LED at the foot switch also appears to be responding, can I rule out a defective uln?

[Rico Coolen]

Found the error.
Faulty ULN2003.

[JohnClark]

Yep! That would do it!

Sorry to not be much help in a timely manner, but glad you got it solved.

[Rico Coolen]

No problem John. I am glad I was able to fix the problem.

[Vorg]

Hello! I've got the same problem, though I actually replaced both IC10 and IC11 (2 x ULN2003) under suggestion from Ben @ VoodooLab and… https://www.youtube.com/watch?v=dsenF9xnDlw here's the result AFTER the fix, nothing changed.

If it might be of any help, I purchased those chips on eBay and I'm aware there have been several cases of fake ICs, but having swapped both the ULN2003 I guess if both were fake, I'd have seen nothing on any segment or a completely different behavior anyway.

I tried getting back in touch with both Ben (privately) and VoodooLab support but haven't had any reply in a couple months so far… if it's not the ULN2003… what could it be? Thanks in upfront to anyone who'll chime in!

[Rico Coolen]

To be absolutely sure, you can buy "real" uln from a real electronics supplier. Then you know for sure that you have official ones. Then you can slide this ocer to the current one (without soldering it loose). Not the neatest method, but you can quickly rule out that it is certainly not your uln that is broken / fake.
Furthermore, your problem is very similar to my problem. Outside the segment, an LED above the switches was less bright.
I also noticed that the display blinked more. That was fixed after the fix.
Be sure to check all soldering.