Technics SA-424 Heat Damage Question

[greenkoala]

I am new to vintage audio equipment, but I am trying to rebuild the system I had when I was younger which was Technics-based.

I picked up this SA-424 Receiver and while cleaning it up noticed that it has some very obvious heat damage on the PCB and it runs very hot there (179 degree Fahrenheit).

I was very happy to find this receiver even though it is not particularly high-end, but is this sort of damage fixable? Is it dangerous?

Here is a photo

 

[2N697]

Welcome to AK, greenkoala! You definitely have some heat being dissipated in that crowded area, but I have seen worse. It would help to see it from the bottom. Do you have schematics for the unit, so you know what those resistors should measure?

 

[greenkoala]

Thanks for the quick reply. I did download a schematic and after probing around with my thermometer found the hottest component was R719, which I looked up and found this info:



It is 40 degrees hotter than everything else around it. Although the neighbor pieces sure are hot. I do not yet have equipment for measuring anything outside of temperature, but I am guessing that would be helpful, so I ordered a multimeter. So I should be able to do my first measurement with that soon.





I removed the back and on the reverse temp is getting to 150 degrees Fahrenheit right under R719.



I went online to look at other people who are selling these same receivers. One had a photo they had taken where I could see this same area, and it appears to have the same heat damage. I took a screenshot of their photo.

 

[cademan]

Don't over think it. Yes, it does get hot, but as long as it is factory and looks like no one else has been in there, it is fine especially if it is working properly.

Them big turqoise resistors are high watt power resistors and are designed to dissapate a lot of heat. Normal.

 

[2N697]

I agree with cademan that the board looks like it is in good enough shape, especially considering the age. Having said that, I see a couple of those solder joints in the bottom view that I would want to have a closer look at. Hard to say for sure due to the resolution of the photo; there is one close to the middle of the photo that looks sunken, and then that larger one toward the top of the photo near the center that has what looks like some sort of precipitant.

 

[teal'c]

Heat is the enemy. The cooler you can run the better. You can always add a fan. Something fancy like this. Has temp sensors and auto on/off, or just get a 12v brushless fan with a low noise rating and decent cfm, and a variable voltage wall wart.

 

[elnaldo]

I'd resolder that PCB. Poor connections (broken solder) generate more heat and burn the pcb traces. Increasing the resistor wattage could help too. And reinforcing the pcb traces with solder will be good too. I usually scrap the burned traces and cover them with solder.

Also, carbon conducts electricity, so any part of the pcb severe burned that turned into carbon should be fixed or isolated.

 

[greenkoala]

Thanks for all the replies. I am a little less nervous and feel like I am already learning a little about what will be involved as I put my system together.

 

[OMGCat!]

If I’m restoring a unit and I see damage like that I’m inclined to replace the resistor and have it sit higher up on the board to allow some airflow and let the leads shed some heat before going into the board.
There are leads bending pliers you can buy to set the height and stabilize while you are soldering. You could also use ceramic or Teflon spacers on the leads to set the height.