Retro Duo Portable Repair
2019-02-05 22:58 - Making
The Retro Duo Portable is the portable version of Retro-Bit's clone consoles, which play original game cartridges. A while back I rescued one from the trash. It didn't (quite) work. It could play games, but the screen constantly flickered. I had plenty of early ideas, and for the past few weeks I've spent an hour here and there on evenings and weekends trying to repair it.
One of the first things I did was just open it, to try to see what was going on inside. I don't remember specifically what I tried first, but it was minor. I tested the system again before fully re-assembling, and voila! It worked great! So I reassembled it and ... it wasn't working again. After a couple experiments, I found that if I pushed on the front, between the face buttons and the screen, with modest pressure (in fact, pushing the buttons themselves could trigger the failure as well) then the screen would start flickering. One of the screws that holds the thing together would, itself, apply this same pressure.
With it "working" (and open) I could confirm that really what's happening is a constant trigger of the "contrast" (brightness, really) button's control. In fact, if you hold that button down, it stops. Inside, there is a weak pull-up resistor on a signal line, and pressing the button closes a switch which (strongly) shorts that line to ground. The system triggers on the change of the signal, and somehow only when being pressed, some other signal line was leaking into the brightness control, causing constant and repeated changes of value, which it interpreted as constant pushes of the contrast button.
The first thing I tried was liberal application of tape (kapton and "electrical") to prevent shorts. In the close up picture you can still see a few pieces, which weren't worth removing now that they're in place. I tried all sorts of clever things with the electronics to try to isolate exactly where the failure is coming from, and eliminate it. None of these attempts helped at all. Somewhat in desperation, with no reason to believe it would help — but I was hoping for some sort of structural, rather than electrical, support — I stuck a bit of card inside. Especially in the second close up picture, you can see that there's one spot that it's pinched enough to leave marks on the card. (And the same thing in a second spot, after trimming and rotating the card to fit better, without blocking any of the screws.) Some thin kapton tape (and, I think, a layer of electrical tape on the other side during one try) just wasn't enough. But this card in this location separates or supports something in the right way, and it's all working again! Perhaps with use it will wear down? For now, it's nice to be repaired.
I could buy one of these brand new for around $80. But now, it will always be that one I rescued from the trash, and fixed up.
