The problem with the Apex is not with the remote, it's with the box. I know this because I've recently fixed the "weak remote" problem my DT502 was having. I can now stand at the end of a 32 foot long hallway and work the box. I can now work the box with two layers of blanket over the remote from 12 feet away. I can now bounce commands off of any wall and still hit the box, even from the next room. I still get the occasional "button bounce," but that's a separate issue and there's nothing that can be done about that.
The Apex "weak remote" problem stems from the fact that they used an inexpensive infrared (IR) receiver module. One that's very susceptible to noise. (Room light, EMI, etc.) And to compensate for this, they used a type of smoked plastic for the front that filters out about 80% of IR. Hence, the weak remote problem. They made the problem even worse by only providing a small window in the black plastic bezel for IR to enter. The IR receiver sits about 3/4" behind this window, so it suffers from something akin to tunnel vision.
The fix involves replacing the original infrared receiver module with one that has a very strong immunity against noise, AND to punch a small hole in the smoked plastic so that the new module can see out. - Just removing the smoked plastic will dramatically improve sensitivity, but it will also cause the IR module to eventually stop working. It just gets swamped by all of the noise and locks up. You'll then need to unplug the box for awhile to get it working again. - And just upgrading the infrared receiver module without making a hole for it to see through will provide little if any improvement as the smoked plastic attenuates SO much IR.
Below are some photos of my box. I used a quality infrared receiver module from a late model ReplayTV DVR. ReplayTV's infrared receiver modules and remotes use a 36kHz center frequency. I'm not sure what center frequency the Apex uses, but since this ReplayTV module works SO well with the Apex remote, I'm assuming the Apex is either 36kHz, or (probably) the MUCH more common 38kHz type. There is "some" frequency leeway in all of these receiver modules, so either a 36kHz or a 38kHz receiver will work great. But I’d be willing to bet the Apex uses 38kHz.
The hole I punched is 3/16" in diameter. I used a Whitney punch, not a drill bit. If you use drill bits, start small and work your way up. The plastic is somewhat brittle.
Using the eraser end of a pencil, and working from the inside, apply gentle steady pressure on the lens. Push just until you can get some toothpicks underneath. If you SLOWLY roll the toothpicks towards each end, the lens (and tape) will pop off intact.
The small window opening. At first I thought this was the sole problem.
The new module's installed and positioned so it will be right up against the back of the plastic lens when it's reinstalled. (Notice lots of finger room from previous testing.)
Finished. Even though you can see some silver metal through the hole, I left it like that as the shiny surfaces should help with off-axis performance. But you can hardly notice the mod in normal room lighting.
If you don't have a well-stocked parts box, the PIC-2031SMB infrared receiver module is a good choice, it's just impossible to find locally. There are lots of other good choices out there though, just look for the proper pin-outs, 38kHz, and very good immunity against noise. Included below is a diagram of what you're looking for. It shows basic dimensions, but more importantly, the correct pin-outs for the Apex. If the module has a metal shield around it (better modules do) that shield should already be connected to the center pin (from the factory.) Also, standard static precautions apply as a lot of these modules are CMOS.
Of the boxes I've used, the Apex DT502 is the one I use the most. I can't believe I've waited so long to fix this annoying problem!
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