522 / 625 Demodulators - we're cookin' with gas!

[phat_bastard]

Pepper brought to light in another thread his theory that the video corruption and audio dropouts that the 522 & 625 have been plagued with are temperature related (and not directly related to hard drive temperature). I wanted to post this picture of the bottom of my spare 522 mainboard as evidence that his theory may be correct.



I'd venture a guess that if you turned your 522 upside down when it was this hot and maybe gave it a light tap you'd make short work of removing / desoldering many of the components inside the demodulator shields.

 

[Smith P.]

Look likes, you got satellite tuners overheating; those demod chips are located in second line from coax connector.

 

[Pepper]

Wow, I just tore into my spare, and it has those same dark stains. The top side also has a brown tint around the edges of the Broadcom chips, sort of like the solder or at least the flux material has been melted too many times. These suckers must get extremely hot.

I wonder if there's any way to attach a big, fat heat sink to that tiny chip without altering the RF characteristics? It looks like it would be possible to do so if I could find something to fit within the space.

 

[phat_bastard]

The real suck of it is that adding a heatsink will only have marginal effectiveness with no air circulation inside the shielding. Either way, this points out a serious cooling deficiency.

 

[phat_bastard]

After giving this some thought, maybe the best way to effectively cool these guys is to sink the bottom of the board to the chassis with a couple slugs of aluminum and some heatsink grease. It's less than optimal, but Thompson does it in some of it's DBS receivers.

 

[Pepper]

I guess the trick would be to make sure nothing gets shorted when placing a piece of metal in direct contact with the board.

 

[phat_bastard]

You'd want to use a dielectric strip where it made contact with the PCB.

 

[Smith P.]

you can make a few holes at bottom of the case close to sat chips and install there slim fan internaly or externaly

 

[phat_bastard]

I think it would be best not to modify the case if at all possible. Sinking the board to the case bottom would be the least invasive method to accomplish this.

 

[Smith P.]

Since you begin modding the receiver ( I guess it your, not leased ) you could select any method what works for prevent frying the chip.

 

[phat_bastard]

If you were to put a fan in the bottom of the chassis it would have to be external, and I don't think I'd want to do that except as a last resort. The standoffs the board mounts to are relatively short, and I don't think I've ever seen a cooling fan (much less a decent ball bearing one) that was .250" or less in thickness so there's no way to fit a fan internally in that location.

 

[Smith P.]

I have two of them ( from SAN switch ).