Denon avr-x1200w thermal protection on startup?

[nightrider0614]

Hi, working on a denon that goes into thermal protect right after turn on. The heat sinks are cold.

I took a meter to the outputs and they look ok. If I put the system into protection bypass it seems to run ok, but I didn't try sound.

Anyone know if those thermal transistors in the heat sink are prone to failure? I have 2 units doing the same thing, looks like voltages are ok tho.

Thanks,
Jeff

 

[ief]

Can't you just unplug/ desolder the thing and see if it fixes the situation. (seen mentioned here and there it could be an issiue)

 

[nightrider0614]

So I've tested the 7 thermal transistors on the heat sink. None look shorted, checked the outputs and didn't see a shorted or open output transistor.

I am getting 1.1 volts on the thermal_protect_a line. Guess I will be pulling the hdmi board and shooting down from there.

Thanks

 

[MAAC0]

Bad sensing resistor or cap out of value, Cracked Solder ?? Heat over the years can do nasty things...

 

[nightrider0614]

The interesting thing is it works when I put the unit in protection pass mode. I don't have a 1200 service manual but found a 1100 one (I think they are just different model years)

The heat sink is not getting warm and the hdmi board chips seem normal temp. I checked a few resistors and they looked good, caps don't seem bulged either.

 

[sajti]

So I've tested the 7 thermal transistors on the heat sink. None look shorted, checked the outputs and didn't see a shorted or open output transistor.

I am getting 1.1 volts on the thermal_protect_a line. Guess I will be pulling the hdmi board and shooting down from there.

Thanks

That transistors are responsible for bias setting. You have find the single thermal sensor, which activate the protection. Maybe we can help, if You share the manual.

Sajti

 

[nightrider0614]

This is the one I've been using

https://www.manualslib.com/manual/997348/Denon-Avr-X1100w.html?page=95#manual

 

[sajti]

Ok I see now. There are thermal sensor for each channel. All looks fine? And there is a thermal B line, but I didn't check where does it go.

Sajti

 

[nightrider0614]

There are 4 sensors on thermal a and 3 on thermal b. Thermal b is fine, gonna try to see if I can figure out which one is pulling the line high.

After using protection pass mode it will come on for a few minutes sometimes but will go back into thermal eventually.

Thanks!

 

[sajti]

Thermal b is fine,

Thermal A is high?

Sajti

 

[nightrider0614]

Correct, I know it's on the main board, therm a and test fine with the connector disconnnected at the hdmi board. I checked the 15k resistors and they seemed fine. I'm going to get the voltmeter on the therm b side and see if I can track it down to which channel is bad. Don't have any freeze spray so I may just turn a can of compressed air upside down and try that first.

 

[nightrider0614]

Thank you everyone that chimed in to help. It's up and running now, another receiver saved from the dump.

The fix? I checked all of the thermal devices, they ohmed out good. I then check the smd transistors (I hate smd devices) and found a transistor that read different then the rest.

I then pulled the .1 uf pillow cap and checked it, it was good. By chance I measured the line between the thermal device and the transistor. .25 ohms! I check the other channels and they were at 0. Turns out there was a bad solder joint on the transistor and the thermal device.

Fluxed, resoldered and put it back together and it's functioning.

From what I can figure out, when I put the unit in protection bypass the transistor heated up and the connection was fine. Let the unit get cold and it went into thermal protect mode.

It's miller time!