The culprit - A new to me Denon AVR-S740H. Protection history shows 60 instances of thermal detector (A) shutdown.
Powering it up for a few minutes and it gets noticeably warm on the bottom of the case where the +12, -12, +5 voltage regulators are. After 20 minutes I would call it hot, and approaching too hot to keep your hand on that part of the case. So the thermal detection is doing its job and not tripping erroneously.
The heat is clearly coming from the small voltage regulators that use the case as a heat sink. It has a bridge rectifier that converts the AC from the transformer to DC, and then the 7812, 7912, and 7805 voltage regulators. A picture of it is below
The manual shows this setup as drawing a maximum of 602 mA.
https://www.manualslib.com/manual/14...page=40#manual
I've tested the amperage on each voltage as it leaves the board and powers the system. Everything checks, with the highest draw being 250 mA on the +12v side. All of the regulators test fine with the diode test but I swapped the 7812 anyway since that seems to be where the heat is coming from.
I'm stumped. With no load there is no heat is generated so I don't suspect a short on the board. With a load, the max draw I can see is well below the design limit and in no way enough to put out that much heat. What am I missing here?
Powering it up for a few minutes and it gets noticeably warm on the bottom of the case where the +12, -12, +5 voltage regulators are. After 20 minutes I would call it hot, and approaching too hot to keep your hand on that part of the case. So the thermal detection is doing its job and not tripping erroneously.
The heat is clearly coming from the small voltage regulators that use the case as a heat sink. It has a bridge rectifier that converts the AC from the transformer to DC, and then the 7812, 7912, and 7805 voltage regulators. A picture of it is below
The manual shows this setup as drawing a maximum of 602 mA.
https://www.manualslib.com/manual/14...page=40#manual
I've tested the amperage on each voltage as it leaves the board and powers the system. Everything checks, with the highest draw being 250 mA on the +12v side. All of the regulators test fine with the diode test but I swapped the 7812 anyway since that seems to be where the heat is coming from.
I'm stumped. With no load there is no heat is generated so I don't suspect a short on the board. With a load, the max draw I can see is well below the design limit and in no way enough to put out that much heat. What am I missing here?
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