Hi all,

Hoping for insight from anyone running a CAC-1587 at 4K120, and ideally a comment from Club 3D.

SETUP

Source: ASUS ROG Xbox Ally X (2025), RC73XA, AMD Ryzen AI Z2 Extreme with Radeon 890M. USB-C DisplayPort Alt Mode output only, no native HDMI on the device.

Cable: Club 3D CAC-1587

Display: LG OLED55CX, HDMI 2.1 capped at 40 Gbps (FRL5)

Mode: 3840×2160 at 120 Hz, RGB 4:4:4, 10-bit, SDR

SYMPTOM

Audio drops out for roughly half a second, several times an hour. Video is completely unaffected, no flicker, no blanking, no dropped frames. Windows never logs an audio device state change, so it is not a driver issue. Audio out of the handheld’s 3.5 mm jack, with video still going to the TV over the cable, is perfectly clean. So the problem lives in the HDMI signal path.

WHAT THE TV ACTUALLY MEASURES

The CX has a hidden HDMI Diagnostics screen (press 1 five times on the remote). With the CAC-1587 at 4K120 RGB 10-bit:

FRL Rate: 5
FFE Level: 3 (maximum)
RS Correction Counter: 32767 (saturated)
Error Count CH0 / CH1 / CH2 / CH3: 99 / 101 / 102 / 99

An Xbox Series X on the same TV, same panel, identical mode:

FRL Rate: 5
FFE Level: 0
RS Correction Counter: 0
Error Count CH0 / CH1 / CH2 / CH3: 0 / 0 / 0 / 0

So the TV is asking the CAC-1587’s converter for maximum transmit equalisation and still logging uncorrected errors on all four lanes, while asking a native HDMI 2.1 source for none at all in the same mode. HDMI audio rides in data islands inside the blanking intervals with much weaker error protection than video, which would explain why only audio breaks.

WHAT I HAVE RULED OUT

All four HDMI inputs on the TV, identical results
4K60 as well as 4K120, FFE stays at 3 even at the lower FRL3 link rate
8-bit instead of 10-bit, no change to FFE or the RS counter
HDMI Ultra HD Deep Colour confirmed on for the port
TV firmware and GPU drivers current
The fact that FFE sits at maximum at every link rate I can select suggests the converter’s transmit signal is marginal in general, rather than 4K120 10-bit being too demanding.

One other thing: the HDMI end where the converter sits gets very hot in use. Hotter than I would expect. No idea if that is related but worth mentioning.

QUESTIONS

Anyone else running a CAC-1587 at 4K120? If you have an LG TV, could you check your FFE Level and error counts and post them? I would like to know whether FFE 3 is normal for this converter or specific to my unit.

Club 3D, is FFE Level 3 expected behaviour here?

Are there hardware revisions of the CAC-1587, and is there any converter firmware?

Would a shorter cable meaningfully help, given the long DP-carrying section before conversion?

Happy to post photos of both diagnostic screens if useful, including the Xbox reference shot.

Thanks.