A few months ago, some Retroid Pocket Mini users began reporting issues with the Mini's display. Apparently, when using high density CRT shaders, content was not reflecting the advertised 1280x960 resolution of the 3.7" AMOLED panel. Instead, people were seeing an effective vertical resolution of ~928p. This RetroHandhelds article provides a good overview of the issue.
As a display panel enthusiast, I had been keeping an eye on the Pocket Mini since release. A 3.7" 1280x960 panel is alluring to portablizers, because it's a 2x integer scale of 640x480, which is the max output res of Dreamcast, Wii and PS2 games. But since most Android handhelds these days use portrait MIPI panels, which are not easy to integrate into portables, investigating the Pocket Mini's panel was not a high priority for me.
Still, I was confused by the fact that no 3.7" 960x1280 panel existed on the market. Panelook lists no such panels, and the NRE for a custom AMOLED of this size and resolution would be at least a few million dollars. Because of the prohibitive cost of custom panels, Anbernic/Retroid/Ayn/Powkiddy have always used off the shelf panels mass produced for phones or other mobile electronics. I spent many hours scrubbing high-end mirrorless camera specs in case this was the screen from a digital camera. In the end, I couldn't find a SINGLE mention of such a panel on the public internet.
When I saw the Pocket Mini scaling controversy pop up in my news feed, I was intrigued. If users were not seeing the advertised resolution, maybe that's why a panel with the advertised specs didn't exist online.
Batocera had recently added support for the Mini, so I took a look at the kernel patches for it. Apparently the panel has a CH13726A controller.
I googled CH13726A. Here are the results:
The results were filled with the 3.92" 1080x1240 AMOLED panel used in the LG Wing. It was mass produced and is widely available from vendors. It was also used in the Aya Neo Pocket DMG, and the Snowcake handheld by Lao Zhang (which is just a repackaged LG Wing phone).
So this is weird-- Retroid advertises 1280x960 resolution on the Mini. But if they're using this panel, how can they be achieving that? The commodity 3.92" panel is only 1240px wide. Here was my thought process:
To test this hypothesis, I purchased a Retroid Pocket Mini.
The panel FPC is not identical to any CH13726 panel on the internet, but looks very similar to Startek ones. Of course, customizing ribbons is incredibly cheap (~500USD). So this is not surprising.
Unfortunately, I had to destroy the front glass to extract the panel.
The teardown confirms a few things:
And finally, here's some napkin math to prove everything out. The bezel size, pixel pitch, and panel dimensions all STRONGLY indicate that this is, in fact, the CH13726-based 3.92" 1080x1240 AMOLED panel.
Conclusion:
Hopefully folks find this interesting. It was a fun little rabbithole to go down!
As a display panel enthusiast, I had been keeping an eye on the Pocket Mini since release. A 3.7" 1280x960 panel is alluring to portablizers, because it's a 2x integer scale of 640x480, which is the max output res of Dreamcast, Wii and PS2 games. But since most Android handhelds these days use portrait MIPI panels, which are not easy to integrate into portables, investigating the Pocket Mini's panel was not a high priority for me.
Still, I was confused by the fact that no 3.7" 960x1280 panel existed on the market. Panelook lists no such panels, and the NRE for a custom AMOLED of this size and resolution would be at least a few million dollars. Because of the prohibitive cost of custom panels, Anbernic/Retroid/Ayn/Powkiddy have always used off the shelf panels mass produced for phones or other mobile electronics. I spent many hours scrubbing high-end mirrorless camera specs in case this was the screen from a digital camera. In the end, I couldn't find a SINGLE mention of such a panel on the public internet.
When I saw the Pocket Mini scaling controversy pop up in my news feed, I was intrigued. If users were not seeing the advertised resolution, maybe that's why a panel with the advertised specs didn't exist online.
Batocera had recently added support for the Mini, so I took a look at the kernel patches for it. Apparently the panel has a CH13726A controller.
I googled CH13726A. Here are the results:
The results were filled with the 3.92" 1080x1240 AMOLED panel used in the LG Wing. It was mass produced and is widely available from vendors. It was also used in the Aya Neo Pocket DMG, and the Snowcake handheld by Lao Zhang (which is just a repackaged LG Wing phone).
So this is weird-- Retroid advertises 1280x960 resolution on the Mini. But if they're using this panel, how can they be achieving that? The commodity 3.92" panel is only 1240px wide. Here was my thought process:
- Retroid is hiding some of the panel active area behind the bezel to achieve a 4:3 aspect ratio
- They are using the full 1240px horizontal resolution and a ~930px vertical resolution. 1240/930 = 1.333 (4:3)
- They are leaning HARD on the Pentile subpixel layout and sheer pixel density, and assuming no one will find out that the actual resolution is lower than advertised
To test this hypothesis, I purchased a Retroid Pocket Mini.
The panel FPC is not identical to any CH13726 panel on the internet, but looks very similar to Startek ones. Of course, customizing ribbons is incredibly cheap (~500USD). So this is not surprising.
Unfortunately, I had to destroy the front glass to extract the panel.
The teardown confirms a few things:
- Part of the panel IS being hidden behind the bezels (the two black stripes visible on the glass)
- The LTPS panel matches the characteristics of the CH13726-based 3.92" 1080x1240 AMOLED, including the slightly rounded upper corners (right side)
And finally, here's some napkin math to prove everything out. The bezel size, pixel pitch, and panel dimensions all STRONGLY indicate that this is, in fact, the CH13726-based 3.92" 1080x1240 AMOLED panel.
Conclusion:
- The panel used in the Retroid Pocket Mini is NOT a native 1280x960 AMOLED panel.
- It is likely a commodity 3.92" 1080x1240 AMOLED panel, with some of the vertical active area hidden behind the device bezel.
- The active area resolution is likely 1240 x 930. This maps to a 3.698" diagonal active area with 4:3 aspect ratio.
- This also corroborates the ~928p resolution observed by community members
- Kernel sources indicate a 1280 x 960 signal is sent over MIPI DSI to the panel. Presumably, the controller on the panel scales this down to 1240 x 930, which is the root cause of the scaling issues the community has observed.
- The reason Retroid cannot fix this issue is because the panel resolution is not what they advertised.
Hopefully folks find this interesting. It was a fun little rabbithole to go down!
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