Working on a Sega Blast City

[Thomas]

It's been 9 months since I received a trio of Cities from kcarcadegame and I'm finally making some progress on the Blast. I underestimated how much time (and money) I would need to spend on these. By a lot.

I don't know how far I will go with restoring the outside of the cabinet. The monitor bezel is very scratched and needs to be repainted. The rest of the paint and the side stickers are scratched and yellow but my current plan is to leave it like that. We'll see. I could change my mind.

Here's what I'm dealing with:

 

[Thomas]

I got the bottom screws out with a Hozan D-332-150, a mallet, WD-40, and a lot of patience.

Everything was very filthy as usual.

The monitor was extra dirty and greasy and I was feeling impatient so I cleaned it with Simple Green and water from a hose. I would rather have taken my time and cleaned it without water and Simple Green but I'm sure it'll be fine.


All clean:

 

[ekorz]

For the extra filth give this a try: Krud kutter. Then water. Then simple green. Then more water.

 

[Thomas]

Both sides under the control panel base were cracked:

Applied Bondo filler then sprayed with paint to seal it:

I put some white paint on the front to cover the crack. It's not a very visible area but I might try to make it look better later.

For the rust, and there was a lot, I soaked the metal pieces in vinegar for a few days:

I've learned that soaking in vinegar and then rinsing isn't enough. To prevent "flash rust", something I'd never heard of until recently, I should have rinsed the parts in baking soda to neutralize the vinegar, then rinsed in hot water, then dried immediately. I didn't do this step but I did do the next step below which is much more important.

After removing the rust I sprayed everything with either CRC Heavy Duty Corrosion Inhibitor or CRC 3-36:

The Heavy Duty Inhibitor has a strong smell that lingers for weeks and it stays a little bit tacky. It also gives the metal an amber color. Other than that I think it will work well. The 3-36 I'm not too sure about. I saw a video where someone tested it outside and the results were good so I guess I don't need to worry.

 

[Thomas]

For the extra filth give this a try: Krud kutter. Then water. Then simple green. Then more water.

Oh yes, I used the Kutter. A whole spray bottle. I couldn't have removed the stains without it. I was tempted to try something even stronger but didn't want to ruin anything.

 

[Anselmo]

These are very satisfying to see. I know the cabs come filthy, but that blast was another level of filthy! Good work, thanks for sharing!

P.S
Krud Kutter is great

 

[Thomas]

I replaced all of the electrolytic capacitors and I use mostly Rubycon because they're cheaper than the other Japanese brands.

I was having some trouble removing solder from the terminal board (a.k.a. I/O board) using normal methods so I used a Hakko 1.0mm cleaning drill and that worked very well.

There are a few "hidden" capacitors that are easy to miss. On a small board on the monitor chassis next to C701 are two SME capacitors. I don't see these listed on the arcade otaku wiki and maybe they aren't included in cap kits. I think they are worth replacing while replacing the rest of the capacitors. There were some bad SMEs in the 90s. These are likely not those. But still might be worth replacing. I did.

There's one capacitor on the monitor adjustment board that's easy to miss that may be worth replacing. Maybe not.

Replaced the power supply fan with a Sunon. It's a little loud but not loud enough to hear during game play. It has good air flow.

 

[Thomas]

The power supply case was rusted so I gave it a vinegar bath, then sanded and painted:

Did the same for the communication port cover:

The terminals on the front power switch and the coin switch were looking bad and corroded so I rubbed them with sandpaper:

 

[mR_CaESaR]

I underestimated how much time (and money) I would need to spend on these. By a lot.

Having gone through varying amounts of work on Three blasts myself, "underestimated" is definitely something that rings a bell

Love the work log mate, I can definitely see the hours of work put in.

 

[snake_eyes_ex]

Looking good.

 

[Thomas]

Having gone through varying amounts of work on Three blasts myself, "underestimated" is definitely something that rings a bell

Love the work log mate, I can definitely see the hours of work put in.

Yeah, I actually thought I'd be mostly done with all three by the end of last summer. If I'm lucky I'll be finished by the end of next summer. That's how badly I've underestimated.

 

[Thomas]

The foam around the light in the back was mostly disintegrated so I replaced it with 3/8" x 1/2" weather stripping:

1" furniture pads for the feet. Grease for the wheel axles:

I can't figure out what this "paper insulator" could be for. But since I have it, I glued it back on.

I gave the foot plate (a.k.a. the step) a thorough sanding, starting with 60 grit and moving up all the way to 3000 grit, then polished with Chemical Guys heavy metal polish:

I had no idea that the Blast City speaker surrounds are usually disintegrated and wasn't happy to see this when I pulled them out of the cabinet. Then things got worse when I started looking for replacements and discovered that there's not a perfect replacement available. Working on the Blast audio turned into a large project on it's own....

I first tried repairing the speakers by following these guides:
https://boomboxery.com/forum/threads/make-your-own-speaker-surround-better-than-foam.10126/
https://nori-take.wixsite.com/repairspeaker

This was very difficult to do properly and my results were not good. I gave up after the first one and bought new speakers instead.

 

[WeinerdogSunflasses]

Great job so far @Thomas

 

[Thomas]

There's a thread here about the Blast City speakers with some good options for replacements. Somehow I wasn't satisfied with those options and did my own search. I settled on the Peerless TC2X4FB00-08 from Parts Express, which I then saw that someone already recommended as a potential replacement. So at this point I feel confident in saying that all possible speaker replacement options are contained in that thread.

Anyway, the speakers are almost a perfect fit. No modifications necessary. The only minor inconvenience is that the mounting bracket is slightly smaller and the screws need to be inserted at an angle in the Blast City speaker enclosure.

Under the magnet I added 1/8" x 1/2" foam to make sure there's no vibration caused by speaker touching plastic.

I also bought new tweeters, the Dayton Audio ND20FB-4 from Parts Express. The terminals in the back needed to be bent back against the tweeter to make them fit. The screw that holds in the original tweeter can't be used but these new tweeters fit snugly. Plus I added some bits of foam on the sides to make sure they don't move.

The woofers are connected in series which brings the total impedance up to 16 ohms, doubling the original total speaker impedance of 8 ohms. This reduces the sound level by only 3dB so it's not a big deal. I didn't connect them in parallel because that would be 4 ohms and I don't know if the Blast amplifier is capable of powering 4 ohms without overheating. Or is the Blast amp only for amplifying line input from JVS and JAMMA audio is powered only by the game PCB?? I don't know. I'm thinking the Blast amp only passes JAMMA audio through the volume knob up front and then straight to the speakers. I'm not sure. I didn't take the time to investigate this. So I stuck with a 16 ohm configuration to be safe.

The capacitor creates a basic high pass filter for the tweeter, just like the original setup. The resistors are there to attenuate the tweeter. (A single 16 ohm resistor in series would serve the same purpose as the three that I'm using but then I would need to change my capacitor value.) With this arrangement I'm getting 14 dB attenuation on the tweeter and a 6 dB per octave high pass filter starting at about 5700 Hz. Sounds great to me. A proper cross-over with a low pass filter for the woofers might be even better but I'm satisfied with this.

Lastly, I added silicone along the edge of the enclosure port before putting the lid back on.

I had some 3M cloth friction tape so I added it around the enclosure. It looks like the same tape that was originally used.

Now, there is one little problem with the Peerless TC2X4FB00-08. And that is the lack of magnetic shielding. I'll write about that next...

 

[Thomas]

As you can see, the woofers are unshielded:

To remedy this I added 22 gauge sheet metal on both sides of the enclosure. I tried several configurations with the sheet metal and this is the only way I was able to fully eliminate all magnetic interference. A single strip covering the side closest to the monitor takes out most of the interference but not all. Both sides need to be fully covered.

Sprayed with some Rust-Oleum paint:

Then attached with duct tape:

Problem solved:

It's a tight fit in the cabinet with the added metal. I had to bend the mounting brackets slightly.

One of the threads was damaged in the enclosure so I tried a new trick: aluminum foil and a smaller bolt size. Works well.

 

[snake_eyes_ex]

Nice fix on the shielding.

Awhile back when I was researching speakers these looked like a solid choice but I was concerned about the lack of shielding for this reason.

This restoration is really coming along.

 

[Thomas]

Nice fix on the shielding.

Awhile back when I was researching speakers these looked like a solid choice but I was concerned about the lack of shielding for this reason.

This restoration is really coming along.

Yes, they are a solid choice. They cost a little more than others and they look more substantial so I went for it, thinking they might put out a good sound. And they do. I knew they were unshielded and decided to deal with that as needed. I was hoping there wouldn't be a problem, and if the speakers weren't so close to the monitor there might not be any problem. Fortunately it all worked out with the sheet metal.

 

[Thomas]

The new speakers and new tweeters sound great and I'm impressed with how full the sound is with such tiny woofers. The Blast City's ported enclosure really helps to pull out some lower frequencies. But once again there is a little problem. A problem for me anyway. With both the game PCB and Blast volume turned to max, the sound level is okay, but not loud. I want it LOUD. So I added an amplifier:

This is the WONDOM AA-AB32189 2x100W TDA7498 Class-D Amplifier from Parts Express. And with 100 watts at 6 ohms it gives me exactly what I wanted. I'm only getting about a third of that power due to my 8 ohm speakers being connected in series but it's more than enough (the Peerless woofers are only rated for 10 watts each anyway). I have the amp set to medium level and with my volume knob at the front of the cabinet turned up less than half way it's very loud, and very clear. My Blast speakers were wrecked when I got the cabinet so I don't know how they sounded and can't make a comparison. But I can say that these new speakers and amp sound much better than the Logitechs in my Astro City. I plan to add one of these amplifiers to the Astro for improved sound and stereo. I expect it still won't sound as good since the speakers aren't in a proper enclosure like the Blast has.

I pulled the original Blast amplifier out, bought some JST connector headers, and utilized the original connections for the new amp and a line output converter.

Original amplifier with JST connectors CN1-CN4:

And here is CN2, CN3, and CN4 routing the JAMMA audio signal through a line converter, to the volume control under the control panel, to the new amplifier, then to the speakers:

The converter and JST connectors are mounted with adhesive Velcro in the spot where the original amp was. I routed RCA connections for the amplifier input and speaker inputs (amplifier output) through the opening of the power supply case where the 32 pin connector is:

No wires were cut and everything can be unplugged and returned to stock condition if I want (not likely).

For power I utilized CN13 on the terminal board. I cut the end off of an AC power splitter and added an AMP UP 3 pin connector. I'm using a power splitter so that I have an additional AC power plug in case I ever add something else to the cabinet in the future that needs 120V AC. The ground wire is connected to the screw in front of the power supply where the other ground wires are connected:

I placed the new amplifier power supply behind the coin box and used adhesive Velcro to secure it in place.

And since I was buying these connectors I bought one to bypass the door switch:

 

[Thomas]

The original volume control is a 100 ohm linear rheostat and that won't work for the new sound system. I replaced it with a 25K ohm logarithmic potentiometer.

The reason the potentiometer wires are removed and separated from the AMP UP connector is because I was getting a lot of hum and buzz noise. I can eliminate the noise by not grounding the potentiometer and line converter but then I get an oscillating noise. So either one or both needs to be grounded. I was able to minimize, but not completely eliminate, the buzzing noise by routing the potentiometer wires away from the AC wires that go to the front power switch. I also needed to add electrical tape around the potentiometer and mounting hole to prevent contact with the monitor frame which was also causing buzz/hum. And lastly I switched from a 50k potentiometer to a 25k for additional noise reduction. I could put the potentiometer down by the amplifier and away from the monitor to eliminate the noise but I like having it in the original position under the control panel. The noise isn't too bad and really only noticeable when game music is silent.

I used AMP UP 3 pin connectors to route the potentiometer wires separately:

The original knob fits over the new potentiometer (needed to file the inside slightly). Electrical tape was added to prevent the potentiometer from touching the metal frame that is not earth grounded and is connected to the monitor:

Routed the wires over the terminal board to keep them away from the power wires as much as possible:

And here's how it all looks:

 

[Thomas]

The speaker grills were becoming detached so I re-attached them using 3M brand 1/4" automotive exterior tape, and some 3/8" weather stripping on the inside to seal the gaps where I wasn't able to re-attach the grills to the cabinet:

Here is the game that I'll be featuring in this Blast City:

Gunbird 2 is a great game but this PCB has a terrible sound problem that someone recently found a solution for:
https://www.arcade-projects.com/thr...improvement-wip-help-wanted.13212/post-311554
The noise is hurting my enjoyment of my new sound system and I'll definitely be trying this fix sometime soon. Probably will replace those capacitors too.

I used some PlastX and Novus polish on the marquee cover. I think the Novus worked better. Used some poster strips and double sided tape for the billboard and Gunbird marquee. Looks nice. Would look even nicer if the Gunbird marquee was translucent.

I added new 1/8" x 1/2" adhesive foam to the control panel base:

The PCB mounting board was missing so I ordered a custom cut mahogany plywood board from Columbia Forest Products (via Home Depot). I mistakenly measured all the way to the front of the cabinet so my board is too long and I can't reach behind it to attach the retaining nut at the bottom. Really not important and I'm trying to not let it bother me.

To mount the PCB I'm using C clamp desktop mount holders with short elastic cable ties: