Can an overheating bga blow out a powerboard?

[dropfry]

Hello, guys. I fixed a monitor the other day, but I don't have a strong understanding of electronics and was curious about how the PFC and a couple of mosfets on the powerboard blew out. Here is what was known about the monitor:

I bought it "as-is" hoping to salvage it for replacement parts. However when I plugged it in it powered up and worked fine for about an hour. After that the monitor's power would be very irratic and turn off and on several times. I opened it up and noticed that the mainboard had a faulty heatsink on the main BGA chip. Not only was it not making contact, but the thermal paste on the bottom of the heatsink was still in fresh factory pattern meaning it has never made contact before.

Going back to my xbox 360 reflow days I decided to reflow the BGA assuming that there was a cold solder joint there. This didn't fix the monitor however and I ended up buying a replacement powersupply. The monitor is now working very well.

I'v heard several reports of people having both the main and power board replaced and I'm wondering if a BGA with a suspected cold solder joint could demand a strange ammount of voltage from the powersupply that would burn up the PFC chip and in turn burn up those two mosfets as well.

I'm even more curious because the guy I bought the monitor from has a few others that are in the same "as-is" condition as the original one that I bought. I'm wondering if I should buy those and reflow the mainboards BGA and if that would prevent the power supply from blowing out. He's already demonstrated that the monitors do turn on, so I know that the PFC isn't blown out yet. Wondering if it's preventable with a reflow or if the powersupply is doomed and on borrowed time.

[momaka]

Re: Can an overheating bga blow out a powerboard?

Modern day power boards are usually quite well protected from overloads. If it has APFC, that means it likely uses a chip that has pulse by pulse current limiting. Such designs are pretty hard to blow up from a "bad" load.

Most likely, the APFC MOSFETs blew because the primary cap is bad or on its way out. If you have one of those cheap ESR meters / transistor testers, pull the big primary cap out of the board and measure it.

As for the BGA going bad - unlikely. Actually, even in the Xbox 360 days, that was rare. In case of the Xbox 360 consoles, what happened was the GPU just ran too hot due to having a much smaller heatsink than the CPU... so it cooked itself and eventually the micro BGA between the GPU core and GPU substrate broke. As with many old AMD/ATI stuff, a quick reheat/reflow could usually bring it back, and sometimes for quite a while too. But the failures on the Xbox 360's was purely due to the GPU heatsink being inadequate, save for maybe the occasional RAM failures once in a while. Ever wonder why the CPU rarely or never failed?

That said, it may be worthwhile to post the monitor's brand and model, possibly in a new thread too. Internal pictures helpful. Please attach using forum's built-in attachment feature.

[sam_sam_sam]

Re: Can an overheating bga blow out a powerboard?

I'm even more curious because the guy I bought the monitor from has a few others that are in the same "as-is" condition as the original one that I bought. I'm wondering if I should buy those and reflow the mainboards BGA and if that would prevent the power supply from blowing out. He's already demonstrated that the monitors do turn on, so I know that the PFC isn't blown out yet. Wondering if it's preventable with a reflow or if the powersupply is doomed and on borrowed time.

I would want to know a few things before I would dive into doing this myself
Here we go

I would want to know is if they all have the same number and are the serial number very similar or close to each other ( not the same exact model model number) I probably would not bother buying them

I would want to know if seller bought them from a store as a “store returns “ if so you might be lucky that have not fried yet but you can not always be sure what the status of any given monitor unless the seller is willing and honest about what the condition of each monitor that they are selling ( to me this would be if-e at best and depending upon how much money the seller is asking for each monitor would determine weather or not I take a chance or not ) that just me and how I think about doing something like this

One note I have taken changes on items that have been advertised as “store returns” and sometimes I have been lucky enough to be able to fixed them but not always just go into as though you might not be able to fix them and can you afford to lose what ever money the seller was asking plus the cost of the shipping

Here is an example of how I have taken a change on buying something that is “not working”
I from time to time I will buy Milwaukee power tool battery packs M18 every once in awhile I will buy a M12
but
Here is what I am looking for in the description dose the fuel gauge light up and how many light up and weather or not it only has one light lighting up is it flashing or ( none of them are lighting ) —> if this is the case I will not even think about buying { unless it is very cheap and including the shipping cost} this situation because there is a very good possibility that the BMS protection board is bad and not worth doing anything with it [ in the other situations most likely battery cells are very badly unbalanced and possibly at the battery end of there life but the BMS protection board is probably still functioning properly and worth the risk of purchasing the battery pack as long as you are not having to pay a lot of money for it *** how I know this information is because I had several battery packs that I own get to a point that they would not charge correctly anymore and what I would do is take them apart to see what the issue is with a certain battery pack is and start seeing certain pattern of failure and I was able to test the individual battery cells because I have a battery testing machine that gives me a lot of information about the health of a battery cell

One note the BMS protection board offered on eBay and AliExpress do not function correctly or not at all this is the reason if I think that the BMS protection board might not be issue with the battery packs that I am thinking about purchasing an the cost of the battery pack and the shipping cost is responsible I will probably buy it

I hope this helps you