Adcom Thermal Protection

[Nuglets]

Hi guys...I'm having a slight problem with my Adcom GFA-5200 Stereo amplifier and I'm hoping somebody can help. The amplifier works perfectly fine and I love it for my PC sound system but it goes into thermal protection on one channel once in a while. Now I need to specify what I mean by once in a while so you can better understand my situation. For the last couple of years I have given up on the amp because it normally goes into thermal protection without even giving me a chance to use the left channel. Recently I decided since it's somewhat useless sitting around not working, that I would make an attempt to diagnose the problem and I think I have a fairly good idea what could possibly be causing it but I'm not an expert with circuit boards so I'm not really sure. I looked at the bottom side of the board where the solder is and noticed that it may have been spilled on near the heatsink in the past so I made an attempt to clean it with rubbing alcohol(not sure if that's the best idea but it hasn't hurt anything so far) and right after I did that the amplifier no longer went into thermal protection on the left channel when I turned it on for a bit. Then all the sudden it did it again so I tried cleaning it some more and I also removed a bit of solder from one of the, what I believe are temperature sensors on the heatsink because it looked as if some of the solder was overlapping two pins, and still had no luck for a while. After a bit of giving up and messing with it I decided to tap on the "sensor" that had the solder removed and it worked again for as long as I wished until I turned it off and came back to it a couple of hours later and the protection came on again. I tapped on the sensors a bit more and now it's working as I type this. I feel like it should be an easy fix based on the fact that the amplifier function perfectly fine when it's not going into thermal protection but I really don't know much about circuit boards and I'm just making an educated guess that those are even sensors. Please help...I'm so close. Thanks and sorry for the horribly long post.

 

[Adam]

Nuglets,

You've got me curious. For the component that you think might be a temperature sensor, can you read a part number on it? If so, let me know what it is. One type of temperature sensor is an AD590.

Also, do the electronics feel hot when they go into thermal protection? It certainly could just be an errant sensor, but there might be something else going on that is actually causing a thermal issue.

Adam

 

[Nuglets]

I'll go find a flashlight quick...I couldn't see it that well when I looked before. The reason I don't really think it's an actual thermal issue is because when it does go into protect mode it is as soon as I turn the amp on. It's been working for about 2 hours with a fan directly pointed at it though and it's fine as of now. Initially it didn't work when I turned it on but I tapped the sensor while it was on and the protect light suddenly shut off and didn't come back on.

 

[Nuglets]

I'm also making some pizza rolls quick if you can bare with me for a few minutes.

 

[Nuglets]

On the top of the sensor it reads "IRF 610". That is the sensor that I was tapping on and removed a bit of solder from. It looks like there are 5 different sensors per channel.

 

[Adam]

I'm also making some pizza rolls quick if you can bare with me for a few minutes.

I can always spare time for pizza rolls! I hope that they were tasty.

On the top of the sensor it reads "IRF 610". That is the sensor that I was tapping on and removed a bit of solder from. It looks like there are 5 different sensors per channel.

From my searching, that appears to be a MOSFET, and not a temperature sensor. The package diagrams show it as a part that has a metal tab on one end (which should have a screw through it to secure it to a heat sink) and three pins coming out the other end. Is that what it looks like?

Those MOSFETS can get pretty hot. Because of the potentially high power dissipations, the package is designed to be hard mounted to a heat sink with a screw through that tab. Could be that the MOSFET has come loose from the heat sink (or board if that's where they put it) and is overheating. Although, I don't think that there is any direct temperature sensing in those parts, but the amp might be set up to trigger a "thermal shutdown" if one of those MOSFETS begins to have abnormal output. Heck, now I'm just babbling.

Sorry to not be of much help to you. I was hoping that it would be the temperature sensor, but doesn't appear that's the case. Perhaps Adcom might be able to help you out. First, though, I'd make sure that part is mounted securely to it's mounting surface and that the bottom of it is making good contact with the mounting surface.

Adam

 

[Nuglets]

That is exactly what it is...the help is greatly appreciated and I'll definitely try to tighten them up to make sure there is good contact. I'm also open to other ideas because I'm not 100% sure that it is that particular chip causing the problem but from my messing around it does seem to be the problem. Thanks again.

 

[Adam]

Nuglets, my pleasure. Good luck with that. It always feels good to get something back up and running, doesn't it?

I agree with you that it sure seems like that part is the issue. I just reread your original post. It could be that the part is not securely fastened to the heat sink, but perhaps one (or more) of the pins is not securely soldered, or the two pins are still connected? You mentioned removing some solder. I'd say check out the pins, too, and make sure that they are securely soldered down.

Again, good luck!

 

[Nuglets]

Yeah it's great that it's working right now...I'm just afraid to put it back together too soon and have it not work as soon as I try it. It is possible that there is still a bit of solder overlapping so I'll continue to mess around and I'll be sure to keep you posted if it stabilizes and works consistently.

 

[Nuglets]

No luck anymore. It just quit working and now I can't get that channel going no matter what I do. I haven't messed with the solder yet so I'll see what happens when I get around to that.

 

[Adam]

Sorry to hear that, Nuglets. That sucks!

Is it showing an overtemp condition, or is it just not providing any power to that channel?

 

[Nuglets]

The channel goes into thermal protection(red LED) after a few seconds of playing and the sound is cut from that channel only. It also does it with nothing connected to either channel(the light will come on after a few seconds of being off and it will go through an endless cycle).

 

[Adam]

Have you had a chance to contact Adcom about this? They might be able to help you out.