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|5th May 2013, 12:12 AM||#21|
More experiments and data collection today, and problem solved.
First, we used the scope to monitor output on the HDMI cable out of the television while the TV was on standby and could not detect any signals.
We then hooked the HDMI cable back up to the unplugged (no power) Dennon receiver and monitored signal from the preamp outputs on the back and could detect no signal.
Then we opened the F5 and monitored from the RCA jacks taking input from the Dennon Receiver. With the following conditions:
1. TV on standby
2. HDMI connected between the TV and the Dennon receiver
3. Preamp output of the Dennon receiver to the F5
4. BUT, with NO POWER to the F5
and we could detect no signal on input to the F5.
As soon as we powered up the F5, we could detect swings between about +2.5VDC and -2.5VDC on the input to the F5. These swings began at about 1 Hz and then gradually increased in frequency.
F5 was powered down and we set up to monitor output from the F5 across 10 ohm power resistors (in place of speakers) on channel two of the scope. Under the same conditions, we saw the identical pattern, except the swings on output from the F5 were from +6VDC and -6VDC (F5 has 24VDC rails unloaded and biased to 1.3 amps). I posted a video of this on YouTube and the following link:
Troublehooting F5 - Dennon receiver - Pioneer HDTV hookup: F5 input and output on scope - YouTube
We connected ground wires from the case of the Dennon receiver and the F5 Ė no effect.
We confirmed that the same phenomena was seen with the F5 turbo amplifier, except that voltage swings on output where higher (rails 30 VDC under load).
So, we then changed out the HDMI cable and the problem disappeared. Everything is working fine with the new HDMI cable.
Perhaps someone will be able to explain exactly what was happening, but I certainly canít. It certainly appears that because of a bad HDMI cable, a parasitic oscillation was set up within the F5 that began quite slow (about 1Hz), and that the signal that set this off was injected into the F5 by the TV through the unpowered Dennon receiver. Fortunately, all problems disappeared with the new cable. Maybe this post will be of assistance to someone 8 years from now with a similar problem.
Thanks for all the suggestions.
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