Recently in Electronics Category

Being an arcade collector, I enjoy a variety of hard-to-find games, some JAMMA, some JVS, but all of them not terribly easy to play unless you have a spare cabinet around with a compatible control panel.  Earlier this year, I set out on the task of building my own supergun: a generic term for an adapter that provides the power commonly used by arcade games (generally just +12/+5v, but sometimes -5v is needed) as well as converts the video, audio and control signals used.  The result worked, but my control panel was raw, to say the least (laser cut by a friend on a single sheet of acrylic: I had no means to support it, the buttons had an odd spacing, and the acrylic chosen was slightly too thick for the buttons to clip in properly).  Also, I relied on a chain of adapters.  Power supplies are hard to get right, so I used an ATX power supply to provide +12v and +5v (note that current revisions of ATX remove -5v; to create this voltage, I used an isolating DC-DC converter that outputs 5v, with the positive output connected to ground).  Similarly, I have games that sync at any of the three common refresh rates: while the vast majority use 15kHz, I have a few 31kHz and a few 24kHz.  15kHz is easy to convert, since it's relatively close to NTSC (and there are dedicated ICs for this purpose), but the other refresh rates are a bit more challenging.  As a result, I decided to use a Gonbes GBS-8220 to convert the video signal.  Sure, it may not be perfect, but the quality is quite decent, the board is readily available at low cost, and the result is a nicely upscaled VGA picture.  Ultimately, this resulted in a mess of adapters, and while the resulting project was fun, it was by no means easy to carry with me (the original goal), nor was it convenient to use.

Enter the Combo AV EX+: an all-in-one JAMMA to VGA or HDMI adapter with a host of options.  The standard configuration from TOPS (a Japanese distributor of used games and control boxes) comes with a two player, twelve button configuration using Seimitsu joysticks.  I'm not a die-hard Sanwa fan, so saving a bit of money here seemed okay.  The control panel itself is beautifully constructed: the case is stainless steel, the control panel is professionally cut out of a nicely patterned plastic, the positioning of the buttons and sticks are compact, but spaced enough to remain comfortable.  The controller also features an internal speaker and 3.5mm jack.  Internally, the wiring is nicely constructed.  The buttons use quick connects (so, if you later want to upgrade to Sanwa buttons, it is easily accomplished), and the parts are largely commercially available.  Internally, the VGA is converted using the same GBS-8220.  The HDMI is converted from that, with what appears to be a VGA2HDMI PCB.  There's also an RGB output for video, but using this requires disconnceting the input to the GBS-8220 to switch it over.  Finally, there appears to be an option to also output composite and S-Video; this appears to take advantage of the GBS-8100.  The power supply is a DIN rail style power supply, common to most arcade machines (note that there are some power supplies that are exclusively 12v or 5v; in this case, the three voltages are converted internally).  Finally, there's a custom I/O board that is able to do rapid-fire on any of the 12 buttons.  The delay is selectable, as are the buttons the rapid-fire assigns to, although I have not used this functionality.

Use is simple: plug in the JAMMA connector to the board (although most boards have the JAMMA connector recessed slightly, so using an adapter to handle this for you) is probably the best bet.  Plug in the power video and switch the power on.  Volume is controlled on the back via a knob, although there are two switches on the back related to the A/V output.  A slider switch selects the audio output: HDMI or the internal speaker.  A small rocker switch provides power to the HDMI output.  The two larger black buttons provide coin input for P1/P2, and the smaller black button is wired to the test switch.  24mm start buttons for each player are also provided, just above the 6 buttons for that player.

Now, for the problems.  First, shortly after receiving the unit, I found that the internal speaker eventually stopped functioning entirely.  I traced this down to the volume knob reading a much higher resistance than it should have been.  Normally, the volume knob should read approximately 0-100 ohms; we were almost a factor of 200 off from that (20 kOhm).  Additionally, this is not exactly a standard part: it's a 100 ohm B-scale potentiometer.  Thankfully, the manufacturer was able to provide a replacement through TOPS, and it was fairly simple to replace myself.  A word of caution here: I'd avoid making any changes to the audio while the game is on, and operate both the board and internal speaker levels at a conservative volume: note that every game under the JAMMA standard outputs powered audio for an 8 ohm speaker in the cabinet.  This is a much lower impedance than the high-Z inputs used by headphones and other hi-fi equipment (it's really just a small amplified speaker).  Even the case uses a 10W rated 8 ohm speaker.  Not sure if anything here was to blame, but better safe than sorry.

The second problem was related to the video: sometimes, in an intense game, the video would scramble, I'd lose a few frames, and it'd pick right back up.  This took me a while to figure out was related to the Gonbes GBS-8220.  At first, it looked like the game was losing sync.  After some troubleshooting, though, I figured out the metal frame of the controller is common with earth ground, but the DC common output was isolated from this ground.  However, whenever the post or shroud of the VGA connector would contact the metal frame nearby, the screen would jump, since suddenly the DC offset has changed.  Eventually, I just worked around this issue by keeping the DC common at the same level as the earth ground by using a short jumper wire.  Not the prettiest solution, but I figured it's nicer than the video signal serving the same purpose. (An alternative would have been to insulate everything with tape, but this looked like it might pose its own unique challenges.

Overall, I've been quite impressed with the quality of the controller.  It functions as advertised, is quite solidly built, and the harness I'm using has a built-in kick harness for games that support it.  Combine this with some excellent support, and I'm satisfied with such a high quality product.

So, if you've read some of my other posts, you'll find I repair arcade games. I also don't like paying outrageous prices for simple parts I can change myself (all discrete thru-hole components), or replacing entire boards if one or two parts will do.

Most recently, I've been repairing an Entropy 2000 Ticket Dispenser (continuous), which is a fairly simple clone of Deltronic models. (Maybe "clone" is the wrong word. Entropy did their own mechanical design, and while it may not be built like a tank, it certainly is a workhorse unit. I have nothing against them.) Anyway, the symptom was simple: tickets would not increment. Similar to Deltronic's original design, the circuit involved here is a photointerrupter, hex inverter/buffer, and transistor with the collector wired to the "notch sense" line in the four-pin connector. Pretty simple. (The schematic is readily available online for those of you curious.)

First guess was the transistor. I had some 2N2222A transistors, so I replaced it, and it worked for a while then quit again. I tried replacing it again, and the same symptom resulted. Clearly, this was strange. The Entropy rebuild kit you can buy from distributors comes with 2N4401 transistors in place of the 2N2222A (okay, this is a fine swap), plus a socket and the inverting buffer, a CD40106BE. It also has a TIP122 (readily available power transistor for driving the motor), and NTE294 (a sub for the hard to find A966 originally used).

Since my initial attempts failed, and I had plenty of parts from the rebuild kit, I figured I'd try the shotgun approach and change them out, having a good feeling that the only part that may help would be the hex inverter. Indeed, there was no change... And actually, the symptom got worse. Now it may only read one ticket before quitting. Physically inspecting the photointerrupter (removing the clear plastic guide, checking it, and reinserting the guide) would let it work once again before running into the same problem.

The original photointerrupter is a SY509, a hard-to-find part with difficult to match physical dimensions. Failing to find this, I went looking for subs. On a hunch, I tried the TCST1202 from Vishay (it was the closest match I could find from data sheet measurements), and lo and behold, it's a nearly perfect drop-in replacement. The clear plastic guide is a little loose, but it fits well enough, and electrically, it's a perfect sub!

Hopefully this tip helps someone else out there; I know it cost me a lot of time to find a match.

As you may know, I do some hobbyist electronics repair.  So far, I've been pretty successful, but the most recent endeavor in fixing a Mitsubishi projection TV with a high-voltage shutdown issue has been... interesting...  In short, I found a company that claimed to be selling a "repair kit" (for way more than it was worth), and I said, eh, okay, if it gets things working, it's worth the cost.  Well, what a mistake that was...

For your entertainment, here's the review I wrote after purchasing (and returning) a kit which didn't come close to matching up to the TV I have.  In fact, $50 for 7 capacitors was... downright amusing.  Oh well.  So, let this be a lesson to everyone.  If you're buying a cap kit, make sure you know what you're getting into.  And, better yet, make sure they actually know what differences between models of TVs are.

First of all, the item I ordered, a "blinking light kit" for a Mitsubishi projection TV was a very expensive "capacitor kit." These aren't uncommon, and I was willing to pay the outrageous price for fewer than ten components that cost far less, assuming they did some work to identify common failures as they claimed. For reference, the components sent from reputable electronics distributors would probably cost on the order of $15 including shipping -- so, they've added some markup... and lots of it.

The order was shipped via First Class Mail, for about what Priority Mail flat rate costs ($7). When the order finally arrived, I was surprised to see the instructions asked me to remove a board which clearly did not exist on this particular model, and replace these nonexistent capacitors.

I decided to return the kit unused (if I'm paying $40 for something that clearly wasn't even researched, I didn't even want to waste the time with their tech support), and accepted the 20% restocking fee. They claim that "once an order ships a restocking fee applies to cover the non recoverable cost of shipping, order processing, parts research, kit build time, and refund processing time." While this may be reasonable, I've already paid for shipping separately (and as they claim, shipping isn't refundable, of course -- I wouldn't expect that). I may even accept that their research is valuable time -- but clearly they didn't research the model advertised (even a quick peek at the service manual would show that the board they describe doesn't exist). In addition, they have an unused kit which still can be resold.

In short, I would not advise purchasing from this company, unless you're desperate and not afraid of disappointment. They did ship the product and process my refund in a timely manner, so I can't fault them for that. Some of their components may be difficult to find through normal channels (but not capacitors, sorry!), so you may have no other choice. If you decide to do business with this company, they will take every last cent from you they can. As a final anecdote, after all their other high costs, the end of their tutorial even has the gall to ask for donations for the author of the tutorial... when in fact, nearly the exact same guide was found for free on other websites.