We’re back inside the Sega TeraDrive Model 3! After leaving the power-supply investigation sitting around for rather a long time, I thought it was about time to finish what we started in March 2016.

First up, I wanted to confirm that the original problem was still there. The power supply had been producing incorrect voltages under load, accompanied by an unpleasant buzzing noise from the internal speaker. Eventually the machine would simply refuse to start properly.

After a little experimenting, the fault reappeared. Wonderful! Well, not wonderful for the TeraDrive, but at least we know we’re still dealing with the same problem.

I’d also been discussing the issue with Ronnie and some of the other knowledgeable people over on ASSEMbler Games. Their suggestions gave me a few places to investigate, particularly around the low-voltage side of the power supply.

There are approximately nine electrolytic capacitors to consider, along with several semiconductor components. One Nichicon capacitor looked particularly suspicious, although I hadn’t established whether it was responsible for the fault. I’d much rather find a defective capacitor than discover the transformer itself has failed!

The power supply is a rather interesting piece of equipment, with a mixture of Sanyo, Nichicon and Rubycon capacitors. There’s even a 2.5 A, 250 V fuse marking on the circuit board. Plenty of components to inspect, and not much room to work around them.

For now, the plan is to gather the replacement parts and investigate the capacitors before moving on to the other components. Fingers crossed we can finally get this TeraDrive behaving itself.

Mains-voltage warning: This is an open power supply containing potentially dangerous voltages, including stored charge after disconnection. This repair work requires appropriate electrical expertise and safety equipment.

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