Vectrex Flyback Transformer Repair - new primary winding

[Richard42]

I recently acquired a malfunctioning vectrex unit (sound worked but no picture) and quickly discovered that the flyback transformer was dead. I went through a lot of trouble looking for a suitable replacement and came up empty handed. I have the impression that this was a very custom part, only used in the vectrex and probably not any other TV, and there are no modern replacements available.

 

During testing I found that the primary winding of the flyback was open (no connection). All of the secondaries seemed to be fine. I came up with the idea to wind a new primary coil, after seeing how DIY experimenters made high-voltage arc generators by winding a new primaries onto random flyback transformers from TVs. After a lot of trial and error, I was able to get this working and bring the game console back from the dead. I hope to inspire other people out there to rescue their Vectrex units with this write-up.

 

Here are the steps that I took to do the final winding, which seems to work almost as well as the original. There are probably lots of different ways that this could be made to work, but this is what I did:

1. Desolder and remove the tin shield around the flyback transformer. I used a memotronics ZD-985 vacuum desoldering station. There is a lot of solder and it would be difficult without a vacuum tool. Be careful not to destroy this shield because you will need to replace it.
2. Desolder and remove the original flyback transformer. Discharge the HV lead going to the CRT (you can use the high voltage probe linked below) before removing it, so you don't get shocked. If your transformer was dead like mine, there won't be any charge there anyway, but take appropriate care.
3. I noticed a lot of corrosion from some evil glue that they used to lock the transformer together, so I removed the steel spring clip, scraped off all of the hardened glue on the ferrite core and spring with a utility knife, and put it back together. This may not really be necessary.
4. You're going to wrap a new primary coil around the empty half of the transformer's frame. But to prevent the wire from rubbing and conducting with the frame, you should put a layer of electrical tape around it first. The inside of the frame is almost exactly an inch long. This will require two strips of tape, each just a bit longer than necessary to wrap around the core and spring.
5. Take some 26 gauge magnet wire, with enamel insulation. Cut a piece that's 3 feet 6 inches long.
6. Scrape off about 1/2 inch to 3/4 inch of insulation on the end of the wire, and wrap it around pin 6. Push the wrapped magnet wire down on the transformer post so that it's below the level of the plastic housing, and solder it there. Pull the wire straight out to the opposite side of the core frame, and bend it up to go along the outside of the empty transformer frame. Glue it to the outside bottom of the tape-covered frame (I used gorilla glue) and let the glue set for half a day.
7. You will now make the winding. You need 22 turns in total. I wound 12 turns up towards the top of the transformer, and then 10 more (crossing over the previous turns) back down to the bottom. You must wind this in the correct direction. As you start, if you view the winding from the top of the transformer looking down, they will be going in a clockwise direction. If you hold the transformer so that the fat part (all the old windings) are away from you, and the empty part of the frame is towards you, with the bottom of the transformer to the left, then the wire will go down in between the frame and the plastic housing. Pull it all the way through, then towards you and up around the frame, then through the middle again and down. Keep it tight as you wind it. With each turn, pull down to create some tension and hold the windings tightly against the frame with your finger on the hand that's holding the transformer, then start the next loop. Don't pull so hard that you break the wire, but try to keep everything tight. You'll make 12 windings on the way up and 10 on the way down. Always wind in the same direction (clockwise as viewed from the top). At the end, put the transformer in a vice and weigh down the hanging wire to keep the windings tight, and put some glue on the top and bottom parts of the winding to hold everything in place. Let the glue set.
8. Bend the small piece of hanging wire at a right angle to go along the bottom of the transformer to pin 7. Cut the wire so it's about 1/2 to 3/4 of an inch longer than needed to reach the pin. Strip off the insulation on the end and wind it around pin 7. Push the wound wire down so that it's below the level of the plastic transformer housing, and solder it there.
9. Re-install the transformer in the vectrex, solder pins 1-7 (pin 8 is unused), and test. Put another layer of electrical tape over the new winding, so that the tin shield doesn't rub off the enamel insulation.

If you really want to do it right, you should use an oscilloscope and a voltage meter with a high-voltage probe (like this: https://www.amazon.com/gp/product/B004PA02Q8) to correctly set R525 and R526. But I think it's not absolutely necessary. I think it is possible to just adjust R525 until the picture is taking up the full screen.

 

This transformer produces a huge magnetic field which is oscillating at about 20khz, and you must put the tin shield back over it. Without the shield, this signal gets into the deflection coil amplifier and makes all of the lines look wavy. The shield attenuates this signal by about a factor of 100, so it is really required.

 

Please post a reply here if you are able to rescue another Vectrex from the garbage heap!