TBC-1000 luma jumping and fading?
 

I have a TBC-1000 with bad luma behavior that I haven't seen reported here.

In the attached "With TBC-1000" video, the luma jumps up above where it should be when the on-screen menu changes. The jump happens after a slight delay which makes it more obvious. After that the luma gradually declines before stabilizing.

The attached "Without TBC-1000" video shows that the luma output from the source device (an old satellite receiver's S-video output, not a VCR) is always stable.

I would greatly appreciate responses about whether this is a known issue. I'm especially interested in knowing if replacing the electrolytic caps is known to fix this. If it's more likely to be an SMD and/or IC problem a repair attempt may not be a great idea.

The TBC hasn't been repaired or refurbished previously.

Thanks in advance!

Nobody else, eh?

Since it has been about a week I decided to expand the testing. I carefully (gently and with ESD protection) opened the TBC-1000 and put a right-angle RCA adapter on the VP-301's internal composite output so I wouldn't have to remove or handle the VP-301 board. The small power board had to be unscrewed though since it was in the way.

The same input source as before was used (S-video output of an old satellite receiver).

The original captures were with a Roland VC-30HD. It was tested again here, and a FEBON100 (USB Video Class capture device that I have for quick "driverless" composite video testing, not for serious captures) was used for comparison.

I don't plan to edit and upload samples unless somebody really wants to see them, but the results are below:

TBC-1000 (internal) -> FEBON100: luma is stable
TBC-1000 (internal) -> VC-30HD: luma is stable
TBC-1000 (external) -> FEBON100: luma is stable
TBC-1000 (external) -> VC-30HD: luma is unstable

The VC-30HD seems to be sensitive to the external/amp outputs from the TBC-1000. Those external outputs (both channels, not just one) are dim compared to the internal output. I'm guessing that the VC-30HD has an AGC that is reacting badly to the not-quite-normal signal.

Definitely a problem worth watching out for with other capture hardware that may have the same or similar sensitivity to flawed signals coming out of TBC-1000s that haven't been refurbished.

Bad luma can be caused by the TBC-1000 front input board/wires, so bypass or swap is required to ascertain root cause. I don't even bother troubleshooting further until this likely issue is eliminated. (But noting it's almost never eliminated, that is the cause.)

I don't doubt that the front inputs are a problem in plenty of cases. In this particular case it's OK after the front inputs since the internal composite output on the VP-301 is stable. It's only after the signal leaves the VP-301 and goes to the amp board that the problem develops.