Bad DC offset on Onkyo TX NR414 - doesn't appear to be in the analogue section

[jjne]

I have a TX NR414, well I have two actually which are both exhibiting the same issue.

The one I've had since 2012 developed DC offset of around a volt under load on the front right speaker output. Not enough to trip the protection but enough to be noticeable in terms of sound quality. I checked the preamp board and couldnt see anything obvious. The offset is too high really to be a drift issue right?

I put the amplifier away for a while. I managed to pick up another example with a dead HDMI board very cheaply (common on these - mine was replaced by Onkyo several years ago). Transplanted my 'good' board into the bad unit. Unfortunately it seems to gave the same issue - a lower offset of 0.5v on the right speaker. Other outputs fine on both amplifiers.

This is leading me to think that the problem is on the HDMI board but I confess the complexity of these things intimidates me.

Has anyone seen similar with these, or have pointers as to where the issue might be coming from? I'm going to check around the DAC next, as IIRC this is on the HDMI board.

[frankusb]

I would think pure audio mode would bypass the HDMI board. Does the offset go away in pure audio mode?

[jjne]

The problem is present irrespective of whether PD is enabled.

I have to say though that I'm now thinking this has to be an analogue issue and I've just been very unlucky to be in possession of two amplifiers with very similar analogue errors. The front right signal is buffered through a DAC on the HDMI board and goes through an analogue switch, but this is buffered to the preamp board via a series 47uF cap, so surely any offset present at the digital, or DAC stages should be removed at this point right? I've checked these caps and they're fine, on both amps.

I just find it strange to say the least if both of these units have developed the same issue on the same channel, but nowhere else.

You'd think as well that this would trigger the protection, but it seems not.

Unfortunately my electronics skills do not extend to being able to work out how the preamp section works - the problem surely has to be in there assuming I'm understanding the DC filter on the buffer to the main amp correctly.

Given that the problem is consistent through all inputs I suspect that if the problem is on the HDMI board, then it's either a knackered output on the DAC, or the switch... But then why isn't this offset being filtered out pre-the preamp by the cap?

[jjne]

Think my next step is going to be trlo try to trace the offset back through the DAC, the op-amp buffer to the switch, and the switch itself. Thinking about it the offset appears when the sources are switched in - when the switch is muted the offset disappears, therefore I *think* this implies that the analogue bits after the switch are not the cause here. I'm still not sure why this isn't being filtered out down the chain but the good news I guess is if it is the DAC, the opamp buffer or the switch, I have spares of these on the bad HDMI board, so this is now a project for when I get the time to look at this properly!