A while ago, the game screen went black during play. When I checked the power board, I noticed that the +5V LED was not lit, so it was time to troubleshoot the problem. There are several test points on the board (shown in the red circles):

The expected voltages at the test points are:

When I measured the board, TP1 was at 3.3V and TP2 showed 3.5V, both far too low.

Transformer Measurements

To check whether the transformer was faulty, I measured the AC voltages:

The readings were a little off, but roughly the same as when I first bought the machine.

Faulty Bridge Rectifier (BR1)

The schematics show that TP2 should have +12.8V and is the first point after the bridge rectifier BR1: I desoldered the bridge rectifier and tested it—it was faulty. I replaced it with a new one, and that immediately restored proper operation.

Recapping and Connector Replacement

Since the power board had previously been recapped using radial capacitors where axial ones should have been, and because that always bothered me, I took the opportunity to:

recap the entire power board with the correct form factor, and replace connector 4J1, which connects the transformer to the board.

Everything is now restored and looks much cleaner.

The controlpanel on the Defender is a 18mm plywood and there is a 2mm plexiglass sheet on top of that.

The overlay is screenprinted on the back of the plexiglass.

When I got it the control panel was in quite rough shape. The upper right corner of the plexi was broken off and a previous owner had cut it and filled it with bondo and put a sticker on top of it and the twoplayer button was missing

Here is an image of the controlpanel as it looked when I got the game.

The first thing I did was to replace all the buttons on the control panel to brand new buttons.

Here are some closeups on the different areas of the original control panel before I replaced the overlay:

I ordered a new controlpanel overlay from England, I is printed on 2mm plex and was supposed to be extremely close to the original, and it was.

There was just one thing that bugs me and that is that the print is not covering the whole plexy. It is a small white line in the very bottom of the panel.

I an pretty satisfied with the result anyway, its much better than the broken one.

The next thing I noticed was that the image was a bit rotated, the height and width is off, out of focus, the colors were hidous and it was pulsating. I need to fix the monitor.

Here is one of the test patterns from the board. As you can see the image is rotated and that the height and width is off

But since this is an old monitor and it does not seem to be renovated at all so I first need to clean it and do a recap.

The next thing to do after cleanup and recapping, was to adjust the b+ voltage that was way to low. The b+ voltage on my Electrohome G07 should be 120V but was as low as 114V.

Next step is to adjust the rotation and puriness so I rotated the yoke a bit to make the image parallell to the screen. I also changed the focus a little bit, while at it.

I adjusted the height a bit but I dont have any tool to adjust the width. Dont use a metallic object to adjust the widht since the width coil is sensitive.

When checking the colors I was surprised that they were so off. I tried to degauss the screen but that did not help much. A little bit better but not much

Here is the colors before degaussing:

Red screen:

Green screen:

Blue screen:

As you can see the colors are bright and strong.. but not very uniform at all. What to do?

I was thinking that this seems like a purity issue and how well the colors line up on eachother.

That will also explain why it feels like the screen is pulsating when the screen switches between the different colors on the title board but not during gameplay.

What I did next was to adjust the purity rings. I started with the puriness on a red screen, and adjusted the first ring on the yoke. After that I turned on both blue and red color from my test image generator and adjusted the blue colour, and finally the green.

The screen turned up pretty good and now it is time to play the heck out of this game.

Until then I decided to take a look at the soundboard that did not work.

I had several issues with the sound card

1. It did not sound anything at all
2. One fuseholder was broken
3. The volume control was inverted and has very short cables, I also missing the metal bracket to fasten it to the cab.

When I first got the game I noticed that there were cables hanging from the soundboard that held a fuse, looking closer I noticed that the fuseholder was broken.

So the first thing I did was to replace the broken fuseholder.

I then hooked up the soundboard to a simple testbed that I made and started to test it.

All voltages looked good when testing at the testpoints.

In the image below you can see the testing points. They are numbered 1 to 4 where 1 is to the left and 4 is to the right.

All voltages checked out fine but there were still no sound.

The board in the image below, that is a donor board that I have, therefore the wrong ROM chip ;)

Next thing to check is the audio amplifier, so I turned the volume up, and was touching the legs of IC1 with my fingers, I heard some noice in the speaker so I then assumed that the main problem was not the amplifier, I then did the thing that you always should start with: reseat all circuits that sits in a socket. And that did it. So the board was not broken, the processor and/or the rom, just needed to be reseated.

While at it, I also changed the speaker from a replaced speaker, half the size it should be and that one also had a broken cone. I bought a new 6,5" full range speaker and mounted it, hopefully it will sound a lot better than the broken one.

Still need to change the speakergrille and the volume pot, but that will be another day.

After checking the powerboard the game did not start at all, it was completely black and all four led:s on the rom-board was lit.

I reseated all the chips that was in a socket and suddenly the game started and I was able to play, but after a reboot I got ROM error on chip 4.

So I then removed ROMs one by one and cleaned up the legs a bit, and then the game started up and is now running fine.

There are still no sound, and the monitor are way off in colours.

The first thing to test is to see if the transformer is giving the proper voltages.

According to the manual and repair handbook the voltages should be:

The voltages are not perfect but I think they might be close enough.

The pin layout is 1 from the left (black wire) and 12 to the right (red wire). The coloring of the wires in the 3d image is not according to the original colors.

Since we have voltage on all pins and they are pretty close to what the nominal values are I dare to connect the cable from the transformer to the power board and start testing. I started testing with the original board that came with the game.

As you can see in these images it is clear that someone has recapped the powerboard. The capacitors are not original and not even the correct ones (the values might be correct though). The correct ones have connectors on the same side, except the big black one that should have a connector in each end of the capacitor.

After a few seconds with the power turned on I heard a small pop and one fuse on the board blew and the 5V LED went black. To me that did not sound very promising so I swapped it to my spare board and tried again. This time no pop and all three LED:s are lit. Feels like I have to order some capacitors for my original board and recap it once again and also check why the fuse blow. That will be another blog post in the future.

On the power board there are three red LED:s indicating that there is voltage out. There is no guarantee that it is the correct voltages though. It only inicates that it is enough voltage to support a LED.

Here you can see the LED:s, you can also see the replaced capacitors on the original board.

In the images below you can see how a board should look like. This is the spare board that I had laying on the shelf.

Feeling more comfortable I started to measure the board. There are 6 measuring points on the powerboard. I did first a quick measure with no load on the board to see if there was anything dangerous. All voltages looked fine and then I connected the mainboard to the powerboard to get some load. If you measure without a load you might get very strange results.

So the voltages are good. The +5VDC is the most critical voltage, the RAM chips is very sensitive to high voltages and above 5.15 volt are not healty for them since they tend to burn.

This means that the power line is ok and not it is time to go to the next step. That is to make a testbed for the boards.

As soon there was an arcade game in my sight I just had to put a coin in it and play. Fortunate there were very few arcade games nearby.

One game that made an immense impression on me was the classic game "Defender".

A few years ago I realized that arcade games was something that people actually had in their homes. As soon as I realized that I started to build my own first arcade game from the ground up and had a Raspberry PI that was running MAME, of course that first game just had to be Defender.

Here is an image of the game when finished.

I was pretty satisfied and it has given me hours and hours of joy. There was just one problem though. It was not an original. It was emulated with MAME on a Raspberry PI, It had an LCD screen, the joystick was a modified 8 way joystick and the buttons were buttons with integrated leafswitches. It was not the same as it was to play the real deal.

I then finally got my hands on a original. The cabinet is in pretty rough shape, previous owner started to clean of the black spraypaint that it had been painted with, but did not succeed very well so it is still sticky. The front still have the spraypaint left and when I turn the game on the screen just shows a mess of colors.

So there is a lot to do with this piece of history before it is in good shape. What I know right now that it is to do is:

• Replace the broken Marquee. The plexiglass is cracked beyond repair. The upper retainer is missing.
• Replace the speaker. The original speaker are gone and replaced with some oval spaker of half the size as original
• Replace the speakergrille. The grill has a huge hole in it and are covered with a smaller grille with bigger holes. As seen in the image above
• Replace the bezel. The original glass is replaced with a tinted plexiglass without print.

• Repair the control panel. The joystick is very sloppy, one button is missing and some buttons are replaced with the wrong colors. The leafswitches looks pretty good though. The upper right corner had a hole that was repaired with bondo and then was covered with a random decal.

• The front was sprayed black so I need to remove that paint. s
• The game itself were playing but rebooted once in a while before shipping. After shipping there are some weird vertical pattern lines that are flickering a little bit. That means that the monitor is at least working but the board has some issues. No sounds either.
• The sound card had one broken fuse-holder
• The coin door has some broken parts, no lock and the mechanics inside are not working as smoothly as the should. There are one missing bulb-holder and the bulbs are of course not working.
• The backdoor is missing so that needs to be replaced. Since this is almost standard that an arcade game are missing the backdoor I suppose that this means that it needs to be rebuilt and painted.

It was surprisingly clean though. Of course it is some dust on the monitor and the chassi but not as much as I have seen on other games.