Recently in Life Category

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.

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.

• I ramble
• I change the topic without any warning
• I will probably go into more detail than you ever cared to know