June, 2012

After recently purchasing another Apple IIgs I brought it home to find it containing a Vulcan GS, a Transwarp GS (!!), a Roger Wagner audio digitizer, and a Chinook 4Mb RAM card.

However, shortly after acquiring the IIgs, the fan in the Vulcan power supply died. No sweat I thought, this should be a five minute fix! How wrong I was... After replacing the fan with a known-good surplus fan I had not in use, I put the Vulcan GS power supply back in and <click!> <click!> <click!> <click!> <click!> <click!>... The power supply was shutting itself down, starting up, shutting down... You could see the power light on the motherboard flashing on and off repeatedly. Damn!

The symptoms are usually indicative of too much load (i.e. a short) or a lack of load. The fan swap was a simple replacement with no soldering (just plugged into the power supply circuit board), so I was a bit surprised. I re-opened the case and checked for anything obvious (foriegn debris, loose wires, etc). Nothing. Hmm... sounds like one of the electrolytics may have died. So a day or two later, I replaced every single electrolytic capacitor in the power supply. I turned it on confident that this will fix it. <click!> <click!> <click!> <click!> <click!> <click!>... Nooooooo!!

I spent ages tracing the circuits and testing here and there... but, whilst I'm handy with a soldering iron, I'm really only a pretend hardware guy - and this was rapidly exceeding my hardware troubleshooting skills.

After a few days of testing and pulling my hair out - I decided that enough was enough! Time to replace the innards of this power supply. I'd heard of others doing this, and I'd already performed the same thing on a normal IIgs power supply using the same strategy as Andrew Webber, however the Vulcan GS is a different beast as the space is very tight. I'd heard of the Meanwell PT-65B being used in the Vulcan GS, and I was initially going to do the same. The local supplier I'd used previously for my Meanwell power supply had sold out and there would be a wait of several months. Hmmm....time to look for another power supply?

And after doing several hours of research, I had found one. Not only does it have the right dimensions, it has a quad output supply. No need to rig up a voltage regulator to derive the -5V from -12V. Yes!

I bought mine from Jameco at the bargain basement price of US$13.50 each (I bought 2).

Here is the installation procedures I used to modify the power supply to fit inside the Vulcan GS:


The original Vulcan internals. Notice how cramped things are?
The new "Red Rocket" EOS MVLT80-4000 compared to the original. The EOS is actually narrower in width, and much shorter in height.
The specifications of the EOS. Notice the quad output?
Remove the mounting brackets from the old vulcan power supply and fit them to the new EOS supply. To fit them to the new supply required a bit of delicate hammering using some scrap wood above and beneath the mounts to cushion the shock.
Time to modifiy the supply to fit the Vulcan power supply case. Unfortunately the coil inductor and line in header need to be moved. In the case of the line in header, I removed this completely. I also removed the 12 pin output header (not pictured).
After desoldering and removing the coil inductor and the line in header.
I mounted the coil inductor onto some spare circuit board I had, and then screwed this onto the power supplies heat sink. Notice that I have used a couple of layers of electrical tape underneath the circuit board prior to screwing it onto the heat sink to ensure no shorts are created. (Please excuse my rather rude mounting holes for the output header).
Wiring up the supply. I simply soldered wires from the original mount holes to the coil inductor. Then I wired up the output header to match the original Vulcan supply so that I could re-use the output cable without any modifications.
A side on shot of the EOS supply. This thing is incredibly thin.
After drilling a few holes into the bottom of the case to suit the new supply, it was time to screw it into place. I put some more electrical tape over the loose wires to keep them from interferring with the fan when it was replaced. I also had to re-drill some of the mounting holes for the hard drive as I had encroached slightly into its original territory.
Put it all back together and voila! We have a working system again. Not only is it working again, technically the new supply is superior - having a higher wattage (80W) and being approved for medical use. Anyone need a IIgs for their next medical procedure?

 

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