What I’ve learned about CRTs in a week

It’s been about a week since the last update. Since that time, I’ve asked a few experts about the display. A few folks have mentioned replacing the “cap kit”, the HOT, and possibly the flyback transformer. Others mentioned checking the monitor chassis. A week ago I had no idea what any of this meant. Today I do.

Here’s what I know:

First of all, the monitor chassis is the printed circuit board on which the monitor components live. This sits underneath the CRT, the cathode ray tube, and larger display tube. Usually, if these old displays go bad, it’s because of a bad component on the chassis.

If you want to fix the monitor, you typically need to order new parts and replace the old ones on the chassis. I’ll get to the parts in a minute, but first a word about working with the chassis. The chassis is hooked up the big display tube itself, what we typically think of when we think of TVs. That big tube holds a lot of charge in it. To work with the chassis, you must remove it from the tube, but before you do that, you must safely discharge the monitor. If you don’t discharge it safely, you may end up discharging through your body, which could either be just painful or possibly lethal. There lots of good tips online on how to do this, so be sure to read up on it before attempting any repairs yourself.

What a “cap kit” refers to is a a new set of capacitors. If you know what type of monitor you have, you can order a new set of capacitors, or “caps”, for it. Capacitors look like little cylindrical batteries. They will typically expand or leak over the years, so it’s a good idea to replace them. If you inspect the chassis, you may find brownish-yellow goop around the base of capacitors. This may mean they have leaked. Other capacitors may also have a bulge at the top. These may also be bad. From what I understand, replacing caps will typically fix issues with bad keystoning in pictures and bad vertical or horizontal alignment.

The HOT refers to the Horizontal Output Transistor. This component is often placed near the flyback transformer (see below) and is usually situated beside a heat sink. I’m actually not sure what problems result when an HOT is bad.

Finally, the flyback transformer takes the input voltage for the monitor and essentially steps it up to several thousand volts. This voltage is applied internally to the display tube. When the flyback is bad, I think the display doesn’t even show anything. You also won’t see any “neck glow” (i.e. the cathode ray tube itself won’t glow when powered on).

There are also integrated circuits (i.e. chips) that may be bad on the chassis. They may also be bad on the “neck board”. That’s yet another circuit board that hangs off the back of the CRT.

That’s a quick summary of all the parts I know of at the moment. Hopefully it will be useful to someone doing a search online…

SF2 Arcade Machine Update

On Monday, I tried out my “repaired” SF2: CE PCB. Sadly, it still doesn’t appear to work. I can’t hear any audio. I tried cranking up the potentiometer for the volume, but it had no effect.

I also tried out the SF2: Hyper Fighting board I got over the weekend. That does work. I can hear audio and can enter the game and use the joystick and buttons just fine. However, the monitor is still showing me a bright green screen. 🙁

I’ve been doing a lot of research online about arcade monitor repair. There is a lot of good info out there, especially on YouTube where people show you how to disassemble the monitor chassis so that you can fix it.

Visually inspecting the monitor chassis (i.e. the PCB for the monitor), I don’t see anything jumping out at me. I’ve determined that this is a Wells Gardener K7000 display. The PCB looks okay. No indication of leaky caps. No leakage on the boards or bloated caps. The flyback appears to have slight cracks in it, but nothing major. In operation, I don’t see any arcing around it, so that seems okay. However, the entire thing is super dusty. Here are some pictures of it.

Look at that dust:

1

Flyback transformer:

2

View from above:
3

Neck (what is that strand I see?):4 Neck board:5

 

I plan on repairing this soon, so if you have thoughts on what might be wrong, leave me a message below! I’ll post updates on this blog as I progress.

Street Fighter 2 Arcade Machine Update

I’ve started investigating the Street Fighter 2: Champion Edition arcade machine and here’s what I’ve found so far.

Power Supply Is Good

The first thing you’ll want to check on an arcade board is the power supply. I took my multimeter and measured the voltage on the JAMMA connector part of the board. At first I read a higher than normal reading. The pc board should be getting +5V and +12V from the power supply. What I measured instead was +6.4V and +14V.

I turned down the knob on the power switching supply until I got around +5.6V. I was still getting +14V out of it instead of +12V. I figured I’d need a new power supply. The next day, however, I tried measuring some batteries and found my multimeter was reading them high, too. I got a different multimeter with fresh batteries in it and in the end, I was getting proper readings. I adjusted it back up to around +5V (and +13V), and it’s good. I figure the +13V should be okay as I’ve read it’s mostly only used by the audio system and it should be okay with that.

Next: Check the pc board

The next thing to try is looking at the printed circuit board, i.e. the game circuit board itself. The PCB is actually in really good shape. It’s very clean and feels like new. Here’s a picture of it without Board C (the top one) attached.

sf2ce-board-bI split up all three boards, A, B, and C. I inspected each one and I actually found a nice little broken trace on board B:

brokenI tested both ends of it with the multimeter and verified it was definitely open. I got a wire and soldered it to both ends to bridge the gap:

bridgedI tested both ends again with the multimeter and it seems good. In this case, it was line 6 of the D bus connector. I traced it to its intended receiver on board B. One of the PAL chips wasn’t receiving this input, so who knows what kinds of errors that was causing.

I looked at board C and also noticed another knick on one of the traces, but according to the multimeter, it isn’t a broken.

Check the ICs

After inspecting for broken traces, I took a quick look at the socketed ICs. I pulled out a few and reseated them, but for the most part, I couldn’t really see any issues with bad pins or whatnot. It’s still possible some have oxidized pins, so I may try reseating the lot of them if it still doesn’t work.

Now what?

I don’t have the arcade cabinet at home with me where I did this work, so I still don’t know if bridging the above made it any better. After inspecting the board closely, I did notice the potentiometer in the bottom-left corner of Board A. That’s the volume for the speakers. I wasn’t hearing any audio last time I turned on the cabinet, so I’ll try turning that up and seeing if I hear anything next time.

One thing that concerns me next is the monitor. After looking some pictures I took of the thing and comparing with pictures of monitors online, I’ve determined it’s a Wells Gardner K7000 monitor.

Apparently, this monitor typically has some real problems with the “flyback”, so I may have to look into that should nothing yet work.

Try out a working board

I ordered a Street Fighter II: Turbo Hyper Fighting JAMMA board off eBay a few days ago and it came in the mail yesterday. I’ll try that out in the machine. The funny thing about this board is that it is in much worse-looking condition than the Champion Edition board I have now. However, the eBay seller advertised that it worked, so it had better. The Hyper Fighting board has some real nasty dust on it and a lot of the parts just look worn. The CE board in comparison looks brand new.

If the Turbo board also does not work in the cabinet, most likely there is something wrong with the monitor and/or audio. Here’s hoping it does work, though, so I can at least narrow in on the CE board.

 

 

 

Got me a Street Fighter II: Champion Edition arcade cabinet

I am now the proud owner of a Street Fighter II: Champion Edition arcade cabinet. It was a big part of my life growing up. At school, we would go across the street to play on the machine at the local convenience store. At Christmas, SFII for the Genesis was at the top of my list when it was released, and of course I got it. 🙂

I’ve always wanted to own a Street Fighter II arcade machine. Even as recent as a few months ago I was considering purchasing one on eBay but I always figured it would be a hassle to order and get into my apartment.

Well, last Friday, I saw an email from a guy at my job saying “Free Street Fighter II machine”. I was skeptical, so I emailed him and asked if he meant the cabinet. He said yeah and if you want it, just come by and pick it up. I didn’t know where to put it but he said how about sticking it in your office? I was intrigued, so I scrambled and found a guy who had a truck in my building and along with another guy, we drove down to pick it up. It was a little tricky to get this beast into the back of the truck. We had to lean it up against the back and slide it horizontally on its back. It was raining a little bit, too, so we stopped at Home Depot before getting it so I could get a moving blanket.

It was all worth it. I was in awe when I realized that I got my dream machine for absolutely nothing. Here it is:

Unfortunately, it’s not working yet. Check out this video to see what it looks like when it’s powered up:

The next step is to diagnose what exactly is wrong with it. It could be a bad power supply, bad connectors, or even a bad PCB. It’s been nearly a week since I got the machine and I’m now a bit more familiar with how arcade machines work. The arcade board in the machine can actually be swapped for another game, so I am considering doing that to see if it would work. Either way, I’m gonna get this sucker working.