Seasonic Focus Plus 750 Gold PSU Review

Teardown & Component Analysis

Parts Description

Before proceeding with this page we strongly encourage you to a look at our PSUs 101 article, which provides valuable information about PSUs and their operation, allowing you to better understand the components we're about to discuss. Our main tools for disassembling PSUs are a Thermaltronics soldering and rework station and a Hakko FR-300 desoldering gun. Finally, for the identification of tiny parts we use an Andonstar HDMI digital microscope.

This looks to be a fresh Seasonic platform, featuring a full-bridge topology and an LLC resonant converter on the primary side. A synchronous design is used on the secondary side in combination with a couple of DC-DC converters for generating the minor rails. All of the filtering caps come from Chemi-Con (good), while the cooling fan comes from Hong Hua (bad). We don't expect much from Hong Hua, but apparently Seasonic does since it's guaranteeing the SSR-750FX for 10 years.

The first part of the transient filter is hosted on a small PCB located right behind the AC receptacle. A couple of Y caps and a single X cap are there, along with a CM02X that blocks current through the X cap discharge resistor when AC voltage is connected. It also automatically discharges the X cap through the discharge resistor when AC is disconnected. The EMI filter continues on the main PCB with two more Y caps and a single X one, two CM chokes, and an MOV.

A couple of bridge rectifiers (GBU1506) are bolted onto a dedicated heat sink.

The APFC converter uses two UTC GPT18N50DG FETs and a single STMicroelectronics STTH8S06D boost diode. The bulk cap is provided by Chemi-Con and has 560uF of capacity. Although this looks low for a 750W PSU, we measured a >17ms hold-up time (the ATX spec's minimum), so it's all good.

There is an NTC thermistor and bypass relay for protecting against large inrush currents.

The APFC controller is installed on the main PCB's solder side, along with the LLC resonant controller. The former is a Champion CM6500UNX, while the latter is a well-known CM6901T6X.

The primary FETs are four UTC GBT10N50ADGs, configured in a full bridge topology. An LLC resonant converter is also used for boosting the unit's efficiency.

On the secondary side, the +12V rail is rectified by four Nexperia PSMN2R6-40YS.

Filtering caps on the secondary side come from Chemi-Con and belong to its KZE, KY, and W lines. Besides electrolytic caps, a few Chemi-Con polymer caps are also used for filtering purposes.

The pair of DC-DC converters is hosted on small vertical PCB. We dismantled this circuit on a previous Focus PSU, discovering that it uses six Infineon BSC0906NS FETs and a single Anpec APW7159 PWM controller.

The supervisor IC is a Weltrend WT7527V. This IC supports OCP at +12V for up to two channels, even if this PSU only exposes a single +12V rail. The same IC supports all important protection features except for OTP, which is implemented through another circuit. Finally, OPP is usually implemented in the APFC converter.

An Excelliance EM8569 serves as the 5VSB circuit's standby PWM controller.

On the front of the modular board, four polymer and four electrolytic caps from Chemi-Con form another ripple-suppression layer.

Seasonic's soldering quality is good. However, we did find a number of long component leads.

Here are some pictures of the long component leads found on the main PCB. 

The fan is provided by Hong Hua, and its model number is HA1225H12F-Z. Although this is an FDB fan, we'd rather see something from Sankyo Denki, backed up by a relaxed profile.

FDB fans might make less noise, but under tough conditions, ball bearing-based ones are simply more reliable. Moreover, we've seen a lot of FDB and HDB fans lately with plain sleeve bearings and minor improvements (rather than true FDBs). Nevertheless, Seasonic seems to be quite confident in this fan's reliability. Otherwise, it wouldn't provide a 10-year warranty.

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