SGI Fuel Power Supply Repairs

Status: August 2022 - A quick dump of pictures and reference information that might be helpful to people... the journey starts

The SGI Fuel uses an WTX type power supply unit (PSU) which is prone to failure. In fact it is one of the most unreliable things every put into an SGI machine. Not only does it fail but its failure has been know to "blow up" other working components.

Fortunately there was been lots of work done to create a replacement for the dead Fuel PSU using an more standard PC ATX power supply (see links below).

This blog looks at what can can done to:

• Recap an original SGI PSU to give it new life
• Can you convert an PC version of the 460 Watt Sparkle PSU to make it equivalent to the SGI original

For those who just want to use an ATX replacement, I also have links to the various threads and discoveries by the Nekochan team to create the required ATX Adaptor

The SGI Fuel Original PSUs

There are different version of the original SGI Fuel PSUs, including:

• NMB Technologies - GM430WTXW01SSV - SGI P/N: 060-0140-004 Rev:B - this is the PSU that was delivered with first set of Fuels. It is 420 Watt and the model type has "WTX" as part of model. This PSU was also sold as an IT002A430WSW, and the specification for his units have the wiring that matches the Fuel PSUs
• HIPRO - HP-W460GC33 - SGI P/N: 060-0140-007 - This is the earlier uprated 460 Watt PSU
• Sparkle Power (SPI) - Model NO PSP460-60PFN - SGI P/N: 060-0202-001 Rev A - this is the later model 460 Watt PSU and is based on Sparkle PC ATX power supply (see below for differences between SGI & PC version)

On Ian Mapelson's SGI Depot he also lists another SGI P/N for the NMB PSU with the same OEM model in his Fuel Parts list.

Based on reading it appears that each of these PSU variations are all equally prone to failure and in terms of reliabilty there is no preferred option. For a more high spec'ed Fuel likely a higher 460 Watt PSU would be preferrable.

Here is a sample NMB PSU label:

See below for Sparkle labels.

The WTX Specification

The Fuel PSU is not "non-standard", rather it was based on the Intel WTX (Workstaton Technology Extended) standard. There are a few version of the WTX specifications including:

• A PSU without fan monitoring - this is for lower spec workstations
• A PSU with fan monitoring - this is what the Fuel PSU type and
• A PSU with dual fans and monitoring - this is for workstations with multiple HDD and CPUs

The WTX standard was not widely adopted and it rapidly lost industry support. The standad included:

• A Design Guide - get from WTX (or here)
• 460 Watt Power Supply Specification - spec from WTX (or here). Unfortunately the Fuel is not aligned with this specification, but with a poorly documented variant
• 610 Watt Power Supply Specification and
• 800 Watt Power Supply Specification.

The Fuel PSU does not appear to be aligned with 460 Watt specification, rather is uses an Intel WTX variation.

Here is draft wiring analysis:

This needs confirmation but based on generally reliable info it looks like:

• P12/P24 - Fan-C/Fan-M  respectively and there is no -5V DC with SGI Sparkle (note that -5VDC is part of ATX spec but not part of the WTX one)
• P3 - is +3.3V SENSE line according to Peter Human site (the WTX spec has Brown == +3.3V AUX , Auxillary)

NOTE: WTX Specification uses "Common" (COM) rather the "Ground" (GND).

The SGI Sparkle vs the PC Sparkle

The SGI Sparkle differs from a standard ATX PC Sparkle by having:

• Monitored 3-wire Fan (the PC has a two wire fan)
• An extra circuit for the 3-wire fan
• WTX Wiring rather than ATX Wiring

Here is the label of SGI Sparkle:

The Fan Controller board is a small circuit that includes a Hitachi Semiconductor HA17393 chip. It takes 12v input and has power output/input to 3-Wire Fan and output to WTX fan monitoring (which on Fuel is via Dallas DS1789 environment monitoring chips):

The backside of the Fan Controller board has some capacitors on the back:

The circuit looks pretty trivial and could be readily reverse engineered.

The other difference between the PC ATX Sparkle and the SGI WTX Sparkle is the 3-Wire Fan:

Both PC and SGI Sparkle have Nidec Beta SL fans but the model is different:

• SGI/WTX Sparkle - Nidec Beta SL Model D08T-12PU A with 3-Wire Fan
• PC/ATX Sparkle - Nidec Beta SL Model D08T-12 PU with 2-Wire Fan

Neither of these fans appear to be manufactored any more but doing web search does find some potential sellers. There is likely a compatible replacement and assuming the airflow specs are the for both versions then this could be used to source an alternate.

Another variation between PC/ATX Sparkle and SGI Sparkle is inclusion of -5V DC power, which is as per ATX specification and documented 0n label:

See above "The WTX Specification" section above for ATX/PC Sparkle vs. SGI Sparkle wiring details.

Recap your PSU

The ATX Option

References and Links:

Intel WTX Specifications - via Web Archive, the "nice" version with menu and the near final version via Web Archive and "Design Guide" & "460 Watt PSU Specification".

Intel WTX Variation - this appears to be closest to Fuel and is documented at Pinout Guide, which says that this was used for 860 and first gen Pentium machines. This wiring pattern is not defined in the WTX specification

Hitachi Semiconductor HA17393 - the fan monitoring chip with the SGI Sparkle

Nekochan Fuel PSU Replacement Thread - way back when the nekochaners cracked the nut on how to use a PC ATX PSU in a Fuel. Key contributer was Kuba Tyszko, who continues to make the "ATX Adaptor" for Fuels available on Tindie and eBay

Peter Human - has yet more Fuel PSU repair and wiring information, this provided confirmation on P12/P24 which are as per Intel 860 variation...

NMB Technologies - provided the original Fuel PSU (GM430WTXW01SSV) which was also sold as IT0022A430WSW. This has the same wiring spec as Intel WTX variant and is also referenced by the Tyan Thunder i860 S2603 User Manual "This motherboard requires a dual Xeon-compatible power supply, such as the NMB
IT002A430WSW."