jjne
Member
Last Activity: 07-28-2025, 05:27 PM
Joined: 03-16-2013
Location: durham
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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... -
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...Leave a comment:
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Bad DC offset on Onkyo TX NR414 - doesn't appear to be in the analogue section
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... -
The analogue inputs are the same. Should be noted as well that if it's switched off and on, sometimes repeatedly, the problem does clear....Leave a comment:
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Yamaha RX V675 sound issues
I have an old Yamaha RX V675 receiver which is starting to develop issues with the sound, although it doesn't quite match up with what folk normally report with these.
From cold, the sound cuts in and out. When this happens the amp is losing sync with the optical input (speaker graphic disappears from the front panel). But this is not resolved by putting the unit into pure direct mode. After a couple of minutes this resolves, although there are occasional clicks from the speakers after that.
At first I thought it was either a speaker relay or the DSP, but I don't think... -
Right, so it seems you have to tie VS to ground to test these chips - and the replacement is behaving normally. I think I have no choice but to risk frying another mosfet, as I cannot see anything else wrong with this damned board......Leave a comment:
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Just to add, the thought had crossed my mind that the reference might be VS rather than ground, however on checking that side of things, although I do see some 50kHz action from VS to HO it doesn't look like a solid signal either, and LO to VS is all over the place.
I guess it's possible it's behaving correctly but I only have a couple of transistors left (bought from Farnell so I'm fairly sure they're good) and don't really want to start burning through them on the off chance....Leave a comment:
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IR21531S odd behaviour
I have a Boston Acoustics Soundwave subwoofer that I'm trying to resuscitate. It was blowing fuses and I narrowed the problem down to the main switching power supply which had blown MOSFETs. These are controlled by an IR21531S.
My understanding of these ICs is they work similarly to a 555 timer and provide constant, and opposing-phase frequency to a high and low output, in this case 50KHz.
What I found was that the LO was oscillating normally but the HO was sat at a constant 12v. This apparently was causing the HO-linked FET to fail. OK, it's a blown 21531, these are... -
Thankyou, that is much appreciated. I think IG was about the only thing I didn't check lol (as 1G is a resistor...).
Will have to transplant from another board temporarily and order some in. Potentially this is good news for this panel if that where the damage has stopped!...Leave a comment:
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AUO M270QAN01 - identify diode?
Hi,
I have a small number of monitors based on the above panel and am working through them. I have at least two with a single, burned-out diode. From what I can see it's something like DI428 or DII428 or DH428. Here's a picture of a working one.
Can anyone identify this please? Based on the number 428 it may be a shottky or a Zener according to Google. The device in question is D105.
ETA I can confirm that the number is definitely 428 (I took a video which revealed a better image), the DII appears to be a maker's mark. There's also a code 1G. Looking around... -
Re: Panasonic TX-L50B6B screen "blotches"
Well yet another LED has failed so I suspect this is happening sooner rather than later.
The LEDs are normally £70 a set, which frankly is a lot to pay on an 8 year old TV... But, I've seen that you can get complete sets from China (this is an LG panel, LC500DUE) for a fraction of this (about £20 or so). Are these cheaper kits any good (I imagine the more expensive ones aren't original LG!) or do I avoid?Leave a comment:
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Re: Panasonic TX-L50B6B screen "blotches"
Thanks for the replies. Hopefully the set will last a while longer (I want to upgrade to a 60-65“ but my current house really isn't big enough for that! ) but if not I'll be pulling it apart and replacing LEDs
Never done it before so hope I don't bust the screen in the process.
Last edited by jjne; 05-27-2021, 05:38 PM.Leave a comment:
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Re: Panasonic TX-L50B6B screen "blotches"
That was my original thought when the first LED went a few years back but I was advised at the time by someone who professed to know what he was talking about that they don't fail in that mode.
That doesn't matter though, if it is indeed a case of two LEDs failing short then I suspect that the TV isn't far from a failure due to, I assume, higher stress on the remaining LEDs.Leave a comment:
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Re: Panasonic TX-L50B6B screen "blotches"
Thanks - I get that but is it actually possible for LEDs to fail and the rest to stay operational?...Leave a comment:
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Panasonic TX-L50B6B screen "blotches"
This post is more a "what's going on here" thing than anything else but here goes.
The above Panny 1080P LED back-lit TV is about eight years old now. About three years ago the dark blotch that can be seen in the lower middle of the image appeared, and it has now been joined by its brother to the lower left. I was able to get used to the first blotch but this second one is annoying.
Both appeared in a similar way. They started off only being dark when the set was first switched on from cold. They'd start off dark, then flicker dark and bright for a while before...Last edited by jjne; 05-23-2021, 05:15 PM. -
Re: Strange problem with an old Nordmende (Videocon) LCD TV
Ignore me, I'm a numpty. Ten years and neither the owner nor I noticed the SKY button on the remote, ahem ��Leave a comment:
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Re: Strange problem with an old Nordmende (Videocon) LCD TV
That's exactly what I will be doing tomorrow morning, I have a Logitech Harmony which I'll be programming and taking across to the set 😁
It is a good run which is why I'm putting some time into it, despite being a cheap TV (albeit made in the old Thomson factory in Italy do there is some quality there) it has been reliable so isn't going to recycling just yet.Leave a comment:
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Re: Strange problem with an old Nordmende (Videocon) LCD TV
True, and I will be testing the remote, but it would be a very strange coincidence if all three of the volume buttons worked and nothing else did.Leave a comment:
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Re: Brand sandstorm
Sandstorm are/were sold by Currys. They are the usual rebranded Vestel/UMC for the most part.Leave a comment:
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Strange problem with an old Nordmende (Videocon) LCD TV
This TV is an old 32", model NU323LD/main board SAX68EDA, from around 2009.
It has worked reliably for a long time, but recently wouldn't switch on from the remote.
It will however start from the side standby button.
When switched on, only the volume controls and mute work from the remote. The remote is functional but the TV doesn't respond to other functions.
I'm assuming something's gone awry with the programming/flash on either the remote or the TV. Has anyone come across this problem before?
I'm going to take a programmed...Last edited by jjne; 06-16-2020, 12:44 PM.
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