Inside the HD135.
The main difference between this and the HD160 is height, and with a 25mm difference there are bound to be implications on the hardware that you can pack inside. The main restriction is height of the CPU fan, and our workhorse CNPS9500-AT had no hope of fitting in without some of it poking out of the top. The HD135 (at 135mm) is, in fact, barely the height of a PSU, so some clever internal real estate magic has had to take place.
Once you remove the two thumbscrews at the rear of the HD135 it is simply a case of sliding and lifting to remove the top. Don't be confused by the two screws at the front of the lid, as these are only there to hold the front edge of the sliding mechanism in place. If you inadvertently loosen these you will cause unnecessary rattle to be introduced to the system. To tighten these without removing the lid you can simply lift it slightly from the edge so the screw holder can grip against something, while you use a screwdriver.
On the underside of the aluminium lid you will find the first of the two temperature/VFD controlled fans, built into a shroud made to fit exactly over the CPU fan or heatsink if you are passively cooling. The sensors, shown above, are not required directly to control the speed of the fan, it can be manually set as a percentage in the VFD software as well, but locating them well will aid in the proper monitoring of your hardware to ensure maximum reliability and extend the lifetime of your precious and expensive internals.
The shroud is adjustable to allow for a seal against the CPU fan/heatsink, though at maximum extension you will have issues fitting anything useful between the CPU and shroud. We will see more about this during the build stage.
Once inside we noticed how well Zalman/DIGN have put the available space to use, with plenty of space for hard drives. In fact, you can fit six hard drives and one optical drive if you chose not to use the external 3.5" drive bay. Filling all six with high speed drives may well cause a fair amount of heat to be generated, so be careful to monitor carefully the internal case temperatures if you do.
A good thing about having so much space is the opportunity to spread the drives around if you are only using two or three, ensuring plenty of ventilation around them. If you look carefully at the first picture you can see the vents both underneath and beside the drive cages, so plenty of opportunity to add a couple of quiet fans if you feel the provided airflow isn't sufficient. Each drive cage is retained by a single central screw on the top of the unit, and once this is removed it simply slides back on the runners underneath - nice and easy to use.
The seven rear expansion slots are screwless, though you can use screws if you are feeling particularly paranoid. They use a clever hooking mechanism, and are all controlled by a single locking arm. I have found this to be an excellent idea, but not without possible downfalls. When using cards that don't actually slot into your motherboard, such as USB expansion cards, you might need three hands to hold and clamp at the same time without them falling out.
Generally, though, the concept and execution are good, and these are small touches that make a good case into a brilliant one. The second picture also demonstrates the clever way the PSU has it's own bay to maximise the internal space and minimise the external volume. Also visible is the second temperature/VFD controllable fan.
As with every Zalman case we have had the pleasure of playing with, this has no sharp edges or ill fitting parts.