Dears, hello from Malta and happy boxing day! I am an audio enthusiast, electronics and automation engineer. I have particular interest in AIWA separates and NAD. I am currently seeking advice regards NAD T750 surround reciever, with an issue it occcasionaly protests and goes into speaker protection mode, particularly in low ambient temperature. Once up and running and warm enough, it holds. Any suggestions am open to. Unfortunatley have been on the lookut to find schematics for the T750 model but could only find T751/2/3 model schematics.
Welcome Trevor, you probably know a lot more than me but 90% of the time I can fix things by doing the easy stuff and your issues requires a bunch of swapping. I'm hoping you already did these things but I'd try the reciever without any speakers to see if it's going into protection. If not I'd try different speakers and speaker wires, animals love chewing on the wires and have been know to cause issues with my equipment. This may be a little beyond the equipment on this forum, if your not familar with AudioKarma, they might be able to help. I'd also check out this thread on DC Offset, you might be able to check your speaker output for anything out of the ordinary. https://audiokarma.org/forums/index.php?threads/amplifier-distortion-dc-offset-and-you.5634/
+1 to what my buddy just said! I spent the last few days researching onto NAD problems and this “speaker protection” failure pops up often... I would start with T751 SM to narrow down onto the Protection module, one post I found thru Google mentioned its full recap because of a zener being next to electrolytics... but you must find it first
Dear Mister X, I have tried with different speakers and also without, and still the same happens. I never really checked the outputs for any present DC offset as AudioKarma article suggests, so must give that a go. Perhaps a full recap may be necessary, only it's tedious and costly considering just the main board is littered with electrolytics! Then the fact it seems to be a temperature related problem maybe it is some capacitor in the end, as that won't be the effect of some resistor. Thanks for your suggestion
Dear Jorge, I fully agree with you and Mister X - may be some nasty DC offset and electrolytic problem - Then knowing the main board's full of them could be the issue. Wonder why whoever did the design opted for so many electrolytics, other than going for some solid construction equivalent for small 1 and 2.2uF caps such as ceramic, mylar or tantalum (cost cutting on a high end amplifier Ughhh!)
I never know how much experience members have so I start with the easy stuff. I have a small pile of equipment that if it looks like a bigger problem then some soldering I shelve it for future consideration. Some of the less experienced members think there's a cause and a solution but it tends to be that one of several issues could be causing one problem. Good luck, if you haven't watched My Mate Vince on YouTube, he has a great way of troubleshooting electronics with limited information. He starts out like most of us and through user comments he's become really good, even with the modern surface mount miniture circuit boards. He's also done some Walkmans and boomoboxes and make you feel like you could fix anything. https://www.youtube.com/user/mymatevince
@Trevor sorry about my sloppy wording, I meant not a "Full" recap but a "full three-cap" recap of just the protection module. As done here: Repairing a NAD C370 NAD T751 Service Manual (which should be similar to T750) has a separate "Load Board", I would start with a short burst of Freeze-Spray onto it when everything is warm and nice.
a-ha! okay that looks better. I don't recall there is a load board on the T750 but will look around and maybe find out that 1237HA chip and peripheral components. Thanks
