|by Michael "SKYMTL" Hoenig | June 25, 2008|
Under the Heatsink
Under the Heatsink
Please note that removing the heatsink will void the warranty on your card.
Removal of the HD4870 heatsink is very straightforward and once it is eased off we have a good view of what makes this card tick. As already mentioned, the PCB layout is extremely clean with all of the power distribution pushed to the back of the card while around the core there are the traces which go to and from the GDDR5 memory. Since all of the decoding and I/O functions are controlled on the R770XT chip, there is no need for additional chips spread throughout the PCB like the NVIO chip used on the Nvidia GTX 280.
The power distribution and voltage regulation area of the HD4870 is a confusing labyrinth of VRMs chokes, resistors and transistors. Interestingly, there are only five small VRMs which had thermal pads placed on them which means that the larger power components do not need additional cooling.
Additional voltage regulation is done by a large Vitec 59PR9853 multi-phase inductor as well as a pair of smaller Pulse VRM modules. Due to their temperature tolerances (up to 125C) they do not need any additional cooling since their large surface area distributes most of the heat they generate. It also looks like the Vitec module can be upgraded to a higher-capacity unit since there are two additional solder points left open.
The R770XT core is not covered by an IHS like some Nvidia cards but rather its polished surface makes direct contact with the underside of the heatsink. It is also surrounded by a metal shim which keeps it in place and secured to the PCB. What struck us as interesting was how SMALL this core is for the amount of transistors it packs.
The memory used on the HD4870 is the next generation GDDR5 memory from Qimonda. Unfortunately, at the time of this review there hasnít been any spec sheets put up so other than knowing that the two banks each operate at 1800Mhz DDR (for an effective speed of 3.6Ghz DDR) on this card, there isnít much other info.
The underside of the heatsink makes contact with the ram modules through a pair of thermal pads while the VRMs have their own separate pad used to transfer the heat they produce. Meanwhile, the base is of surprisingly good quality aside from a few tooling marks and scratches.
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