Last year, I repaired a Vectrex games console for a friend of mine who runs Re:Wired Museum & Arcade CIC, a community-run project in Teesside which helps to preserve and showcase technology that has impacted society. Apparently the unit worked OK for a while after being whacked on the side, then stopped working completely following transit.
I dismantled the unit and inspected it for any obvious faults – the mains input is soldered to a small power board with a fuse, the fuse holder was broken so the fuse wasn’t making good contact on one side, and the live side of the mains cable hadn’t even been soldered and was just wrapped around the terminal post, so no wonder this thing needed a whack on the side to get it to work, both of these were making intermittent contact. I’m not sure if it was like that from the factory or whether the mains cable had been replaced.
I replaced the fuse holder and soldered the mains cable properly; I also fitted a new 3A-fused UK mains plug, cleaned the interior of the unit, flushed out the power switch and volume control with contact cleaner, and reflowed the major solder joints on the mainboard and neckboard to help stop them from cracking in future.
I tested the unit again and it was still dead, so this wasn’t the only problem unfortunately. Apparently a common failure in the Vectrex is the mains transformer, or more specifically the thermal fuse integrated into its primary winding. These are designed to fail open-circuit if the transformer gets too hot, so is a secondary safety device after the main replaceable fuse (250mA slow-blow), however they can become temperamental with age.
I checked the transformer and sure enough, its primary winding was open-circuit, but both the secondaries were OK. The transformer has a centre-tapped 3-pin output with two 9Vac supplies, one for the video circuit, and one for the digital logic – the white wire is typically the centre tap, and the two red wires are usually the two supplies.
The live is fused and connects to the transformer primary (typically a black wire); the neutral connects to the other side of the transformer primary (typically a red wire); a third wire (usually white) also connects to the transformer primary but does not actually seem to be needed, the transformer primary is purely a single mains coil.
Apparently, on some Vectrex transformers the thermal fuse is accessible and can be bypassed without damaging the transformer, so I removed it to give this a go.
The transformer is fairly easy to get apart – it has an outer shield which simply clips together, and there is a plastic shell around the windings which can be carefully cut open and pulled back to expose the internals.
On this transformer, the two sides of the thermal fuse on the primary winding were accessible from the side the secondary cables penetrated into – I bridged these with some wire then measured continuity on the primary and it read 70Ohm, so it was no longer open-circuit. I removed the redundant third primary connection while I was in there, then insulated everything with electrical tape and reassembled the transformer.
I checked the transformer output with the secondary cabling still detached from the mainboard, and I got 11Vac across both secondaries as expected – this will fluctuate with mains voltage as it is not regulated, so will probably be higher than 9Vac.
I reinstalled the rebuilt transformer and tested the machine, and it now works perfectly!
