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TV Repair Sites...

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.

Troubleshooting Dig Dug (Rev B)

So, recently, I acquired a Dig Dug (Rev B) in nearly mint condition, and a Galaga in slightly less-than-mint condition.  Both games worked great, and have been an excellent addition to my little home arcade (with an Ikari III JAMMA cab running Gradius II most of the time, and a Keyboardmania 2ndMIX).  That all changed when I went on vacation: suddenly, the Dig Dug decided it wouldn't work for more than 15 minutes at a time.

I checked the obvious problems.  Checked voltages on the power supply, checked the Atari power brick's filter cap ("Big Blue") using the Bob Parker/BLUE ESR Meter, and checked all the other electrolytic caps.  Finding nothing suspicious, I started looking for things a bit more out of the ordinary.  I even compared voltages before and after the crash on the +12, +5, and +10.6 (unregulated) outputs, and saw no differences.  Even the -29V generated for the EAROM was fine--some levels were a bit high, but not enough for me to be really suspicious.  If I had my scope (it's been on semi-permanent loan to the local hackerspace), I'd happily check to see if there's excessive ripple voltage on any of the DC lines--sadly my DMM isn't a true RMS meter--so putting it in AC mode doesn't remove any DC offset--it just reads bogus values.

I noticed when the game crashed, the output on the monitor went blank.  It wasn't playing blind, even--it was completely dead.  Indeed, using a DMM, I confirmed the !CSYNC line was a solid 5.00V -- so, nothing's syncing anything to the monitor.  Strange.  I tried pulling all three Z80s and seeing a fair amout of oxidation, cleaned the pins, and was able to reproduce the issue, even with the Z80s removed.  Started sniffing around the Y1 crystal -- 18.432MHz.  Indeed, getting CLOSE to this crystal could cause the game to glitch--no sync generated to the monitor.  Turns out this game uses the Namco 07xx custom IC, which is a sync generator.  A CPLD replacement is available, or some new old stock are also available... if it comes to that.  Galaga happens to use the same custom IC, so that could also be used to test.  Still, despite the sync generators getting quite hot, they seem to be a symptom rather than a problem--the sync generator also drives the watchdog reset, which also gets tripped.  I also happened to note that the !RESET signal sits at a place that may be in an exclusion zone for some chips--somewhere between 2-3V (higher when not working--but either way, looks to be okay).  The rest of the clock circuit seems to be a 74S04 hex inverter, the crystal, a 100pF mica capacitor and a 74LS107 dual J-K flip flop being used as a clock divider, as it seems.  The board's 18MHz test point can isolate things down to the 74S04, cap, and crystal, and indeed, that point's DC average voltage does seem to be higher when failed (2.3v vs. 1.07v working).  The presence of the multimeter alone seems to be enough to occasionally disturb the frequency of the crystal oscillator.

So, some things are definitely much easier with an actual scope or true RMS multimeter.  It seems strange that this issue comes about after the game's been on longer, but without pulling a scope in to look at the issue, I may be replacing all three parts in question (although the mica cap probably won't fail--a crystal or 74S04 seems far more likely.  It may still be worth double-checking for AC ripple on the DC voltages, and possibly replacing the "big blue" cap again (or any possibly-affected axial caps on the regulator/amplifier board).

UPDATE 8/2/2013

Ordered a new crystal and inverter, installed it, and so far, everything's been running stable.  Also, an unusual buzzing noise whenever the game was on seems to have gone away, making me believe the problem is indeed resolved.

Why People Suck at Driving

This shouldn't be a revelation.  But in some senses, it is.  I've noticed a few trends driving here in the winter.

  1. Oh shit, white stuff? (And no, not cocaine, kids.)  Really.  The moment this mysterious "white stuff" appears, people's brains immediately fly out the window, and traffic comes to a grinding halt.  The roads could be perfectly fine, but it doesn't matter.  Top speeds are 45MPH in a 70.
  2. We don't need no stinkin' brakes! Shortly after the snow has been on the ground, people immediately believe the roads will have magically improved.  It could be 1 minute or 1 day after the plows go through, but immediately speeds are back up to and BEYOND the speed limit.  All this occurs when there is still visible ice on the roads, so any attempt to stop at those speeds would be an exercise in futility.  Also, it follows that extreme tailgating becomes a popular passtime in this phase.
  3. Traction? What's that?  It really seems that the people committing offenses #1 and #2 are also the people least suited to be in a snowstorm.  That's right, giant SUVs and rear-wheel drive trucks.  Most trucks haven't even bothered to weight the bed with any type of snow, and it shows as they fishtail their way down the interstate.  Also, I see a surprising number of minivans and SUVs along the side of the road, in rather precarious positions from various spins.  I guess the pickups manage to find a way to pull themselves out.  Hurrah for that, at least.
Maybe it's just the county's elitist "I'm better than you, so get out of my way" attitude that is to blame, but really, I'm sick of it.  If you're going to drive like an idiot, please do it in the driveway of your mansion so you can kill yourself and not me.  Thanks.

Update: Another round of this stuff... and sure enough, wrecks immediately.  Always fun when you think, "hm, I think I'll turn here" and your car decides, "hm, no you won't."  But hey, I managed to control it and not cause any extra problems.  Also, remember kids, the (!) light is the "you're driving awesome" light.

Excess of the Electronics Industry?

So, it's fairly well known that boards that can be made for pennies on the dollar frequently go for ten times that amount, if not more.  To some extent, this is understandable, as a lot of engineering time and labor went into designing and producing the boards.  These costs are forgotten when you evaluate the parts cost per-board.  But, at what point is this excessive?

Just the other day, I was troubleshooting a relatively simple board.  A set of infrared LEDs and photodiodes, resistor network, some diodes and assorted resistors, a transistor, visible LED, and a single IC.  All in all, I would estimate the cost of the board at about $40, assuming you didn't want to mass-produce the PCBs and were silly enough to pay for them one-by-one.  The vendor, however (and they are quite reputable, too), wanted $120 for a replacement part.

The way the board had failed wasn't terribly uncommon--the output was essentially signaling that an IR beam was being broken at all times.  The manufacturer gives a relatively good troubleshooting guide for symptoms and their causes, and sure enough, this lined up with what the device was behaving like.  They also give a good set of schematics for the mainboard, but curiously enough, omit schematics for some of the subassemblies.  The troubleshooting guide stated something along the lines of, "If you see this condition, the sensor board is bad and should be replaced."  This was really fishy to me... no way would the entire board be bad.

I check all the photodiodes, and sure enough, they're all receiving the IR beam properly.  My next thought from tracing this very simplistic two-layer PCB was that either the IC or the transistor was dead.  The transistor seemed to be more related to driving the LED as a visual indicator, so I put my money on the IC.  Of course, without a parts list or schematic, determining what this IC was from the chip markings proved a little difficult.  After misreading one digit, I determined the part was an 8-channel Darlington sink array.  The logic diagram on the datasheet showed exactly what was going on: this was essentially being used as a giant NAND gate (really, more like a negative input logic OR, but who's counting?).  I place my order with an electronics supplier for a handful of this IC and the transistor and wait for them to show up.  Part cost for the IC?  $0.80/ea (for singles).  The transistor was even less.

Once the parts arrive, I go ahead and decide to swap the IC first.  After all, it's socketed, and sure beats desoldering the transistor on the board.  I go plug it into the unit for a quick test, and no LED lit.  Halfway there, so I break the beam, and the LED lights.  Yup.  Bad IC.  So, for $0.80 in parts, I fixed a board that the manufacturer wanted $120 for.  Yeah.  Totally makes sense why they wouldn't want to release schematics or parts list, huh?

In short, when electronics die, it's often not worth troubleshooting.  But if the device is simple and expensive enough, it's quite possible you may be able to beat the game and repair your device for far less than a replacement.  In this case, there was absolutely no actual hard work required: just diagramming the circuit used mentally and swapping a socketed IC.  Just look before you pitch something and start over.

Automated Lighting

So, as I mentioned earlier today, over the past few days, I had an idea to automate the lighting in my apartment.  After talking with some friends of mine, I finally decided on a rather simple implementation, wiring relays in parallel with the existing lightswitches (so all the lightswitches will continue to operate normally).  The relays aren't entirely necessary, since the MicroLogix PLC I'm using has relay outputs, but they do provide an extra layer of safety (not to mention all the signalling is low-voltage, 24vdc).  Relays themselves were squeezed into the electrical box where the switches are.  Also, all the contacts on the relay use crimp-on quick disconnects.

The ladder logic program I'm using is fairly simple: use timers to create a maximum length of time any light can be on, and also provide an automated mode where the lights cycle between on/off periods.  Inputs are wired like pushbuttons to toggle each light, as well as the manual/auto mode.  The whole thing works as expected, blinking lights and all.  Enjoy some pictures after the break.

MicroLogix 1000 and Linux (er, Win7)

So, because I'm a geeky guy, and I wanted something fun to play with (and since I've been taking a course on Factory Automation), I went over to America's junkyard and picked up an Allen-Bradley MicroLogix 1000 PLC on the cheap.  Good deal, and while not very featured (doesn't even have analog inputs), it's still something to tinker with.  Also had to buy a 24V power supply and a cable to program it with (which pretty much doubled my cost), but anyway, on to the fun stuff.

I'm a Linux user.  I prefer it, spend the majority of my day working with it, and don't even have a system that will natively boot to Windows anymore.  The one version of Windows I use on any regular basis is a VMware image of Windows 7.  Well, with this new PLC, I wanted a way to keep this trend going.  Maybe the title is misleading (or I cheated), but... it's the best I can do.

First hurdle was USB.  The drivers for the chipset (CP2102) weren't in Windows 7, and the provided drivers also wouldn't work... so it was off to the vendor to find something compatible with Win7.  That didn't take long, and after a quick reboot, that was up and running.

Next, I had to get RSLinx Classic running to allow communication.  Setting up a DF1 device is pretty simple in RSLinx, and autoconfiguring communications worked great with the PLC, but in Win7, I was getting an odd "Could not create registry" error.  Well, I remembered, it's not running privileged, so I shut it down and restarted it, this time running as an administrator. After I did this, it created the registry and started going, so all was happy there.  It also seems that on subsequent starts, it doesn't need to be run privileged anymore, since all the communication parameters are present.

Third, I just started up RSLogix Micro Starter Lite (I'm poor and it does what I need).  Since everything in RSLinx was good, I just tried going online and uploading the program from the processor to see what was on there, and saw there was a pretty simple program.  I mucked around with it a little, forced a few inputs, toggled a couple bits, and saw the state changing appropriately.  Satisfied all was well, I decided to write this and get some sleep.  But, before I go, I leave you with a pretty picture of my accomplishment.  Enjoy.

PLC Stuff - RSLogix

A Beginning

Well, after about five years of not touching a single page on my website, I decided it was time for a fresh start.  You can read a bit more about me in the "About" section... and a few things you might expect:
  • I ramble
  • I change the topic without any warning
  • I will probably go into more detail than you ever cared to know
Given this, over the next few weeks and months, hopefully I'll be able to give you a glimpse at some of the things I've accomplished.  Right now, as summer's winding down, I've been finishing my internship where I've learned anything from how frustrating certain software packages can be to very intriguing things like control systems security.  Along the way, I also had time to develop a simple application called "Acceleroid" to capture accelerometer/GPS data in near-realtime.  Blame that on my interest in roller coasters.  It's been an experience.

Where it goes from here?  Who knows, but the journey has to start from somewhere.

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