notANON

This monitor has been on my desk for months because I’ve been avoiding it but I’ve decided that it’s taking up too much space so I’ve decided to start digging into it again.  I’m going to document my repairs here in hopes that it will help someone else out to see my troubleshooting process.

The symptom of the issue is no picture.

The problems are several.  The monitor is switchable between standard and medium resolution hence the “DS” in the model name which stands for dual sync.  When I attempt to run it at 15k, things seems somewhat stable.  There is no picture but when I test B+, it will sit there right around 130v which seems pretty reasonable.  Testing with the high voltage probe I get about 130v on the anode which tells me something in the flyback/HOT area is not working correctly but I don’t have a schematic so I’m flying blind on it.  When I hit the base on the oscilloscope, I get a reasonably nice looking square wave that seems to be at the correct frequency and looks happy.

So that makes it appear that the driving waveform is ok.  When I hit the collector, I get this:

That does not look good.  Theoretically I should be getting voltage spikes that go well of the screen when the HOT grounds the flyback.  The scope is set for 50 volts per div and I’m barely covering two of them so something is clearly wrong here.

When I switch over to medium resolution (25k jumper) things get much worse.  The B+ pops on and starts at about 140v, then it keeps climbing and the monitor starts getting noisy to the point where I’m concerned and then I shut it down.

I’ve tested the flyback with a ring tester and it looks good but perhaps there is a different problem with the flyback that cannot be diagnosed with that tool.  I know for sure the HOT is good, I have several of them and they all test the same.  When I pull the HOT out of circuit, both the 15k and 25k mode act the same and give the same B+ voltage of roughly 130v.  The only difference is the waveform reading on the base of the HOT.

The opportunity finally presented itself for me to buy a full-sized arcade game.  I suppose I could have picked a smaller one but I kind of bought it on a whim.  The game?  S.T.U.N. Runner.  It’s a sit down “cockpit” style racer with no gas pedal.  It’s a game that I used to play all the time whenever I would see it back in the early nineties.  This particular copy was obtained from the B&I Amusements auction when they shut down in 2013.  I was pretty disappointed to see them go but I thought this was a reasonable souvenir.

The game was not perfect when I got it.  The cabinet and plastics were not bad at all but the monitor was so dim it was totally unplayable.  A recap and rejuv made the monitor really nice again.  There was some other random small issues such as a cracked handle on the steering yoke.  Luckily there is a stockpile of over 5,000 of these at Suzo-Happ.  The Dallas battery powered RAMs which kept high scores were also shot.  Luckily a new comparable part is still manufactured.  I ironed out a most of the small issues but then another one popped up.  The game started resetting randomly.

At first I sort of ignored it because I figured it was just a ghost in the wires or something but then it started making the machine unplayable.  I finally got so frustrated that I ordered a new board set off eBay.  I figured that whatever was making this happen HAD to be on the board.  I put the new one in for a bit and it seemed to fix it for a bit but soon it started again.

Surely the only other culprit could be the power supply, right?  Wrong.  I tried a different one and the problems still continued.  All the was left to look at were the connectors and wires.  I started furiously blasting all the molex connectors with DeoxIT.  After waiting the recommended two minutes and powering it back up, I was hoping to see the end of the resets but did not.  As a last ditch effort, I decided to start unplugging harnesses because I figured something external had to be killing it.

Turns out that not much experimentation was involved after all.  I unplugged the harness going to the volume control and service switch.  I put my son on the game to playtest it for me and he decided he wanted sound again which doesn’t work without the volume obviously.  I plugged it back in live and what do you know?  It reset, right there.  Eureka!  I pulled the service switch and volume bracket and stuck my VOM probes on the switch.  It read overload at first which was fine but then all the sudden started bouncing between 100-300 ohms.  No wonder this poor game was confused.  This switch started conducting if you sneezed on it.

The date ended with me blasting the heck out of the switch with DeoxIT and me needing to list a perfect second board set on eBay.  🙂

It’s hard to tell what went first…  Was it the flyback?  Maybe it’s the mylar with the guts oozing out the side.  The weak green gun on the crappy Zenith A68AGD01X tube?  Perhaps it was a perfect storm but my sneaky suspicion is still that something went first before the rest.  The frusteration came however when I replaced the flyback, all the burnt components and all of the caps and still got no signs of life.

That signaled the time to bring in the rejuv.  I haven’t used a rejuv in years so this was pretty exciting.  One of my friends just picked up a Sencore CR70 off of eBay.  It’s a really sweet box.  Way nicer than the one I used at All Repair back in the day.  This one only has 5 sockets.  You set the wiring diagram but using a series of switches on the unit itself.

Anyhow, we fire up the rejuv and found the green have pretty lousy emissions.  Worst yet, the cutoff didn’t even register on the scale until we cranked the negative bias from the recommended 68v down to somewhere in the 35v range.  We hit it with the auto rejuv 3 times and then with the manual cycle.  This brought the emissions back to the level of the other guns but not the cutoff.  There was a little bit of improvement but it’s a clear sign that this tube will need to be replaced sooner than later.

After rejuving however it still didn’t work.  We had heater and high voltage though so we were a bit perplexed.  We ended up checking the G2 voltage live in circuit.  The most we could squeeze out of it was 190v or so.  This was way too low given that a similar chassis with the identical tube a few games downw was putting out 290v to get a reasonable picture.   We had the Neotec NT-27E service manual so we gave the schematic a once over.   It APPEARED that our fault may have been in the brand new flyback but my friend didn’t want to give up so easily.  he decided to check every pin of the CRT to ground.

Low and behold, G3(focus) was reading less than 1M of resistance to ground.  Not particularly good.  A closer look at the socket revealed that it had gotten really hot.  We picked at it until it opened up and ended up with a handful of carbon residue.  It turns out there is a spark gap inside of this socket.  It had started arcing which produced some carbon.  This led to more arcing until the focus had shorted enough to ground where it was also dragging down the G2 voltage substantially.

For the moment, we yanked the spark gap and soldered the focus wire directly to the focus pin.  Needless to say it fired right up.

Not sure how long this would have taken me to discover myself but it was a darned good find on my friend’s part.  Very impressive.

The Electrohome G07 is a simple monitor…  At least that’s what I keep hearing and seeing.

As simple as it is however, I have not had a lot of experience with the G07.  The majority of my experience has been with 1990’s computer monitors and more recently 1990’s arcade monitors such as Wells Gardner and similar.  Compared to the later monitors, the G07 is completely foreign.  For instance, the horizontal output transistor is mounted off of the board on a heatsink.  It’s insulated from the heatsink to keep it from grounding out because the outer case of the transistor is one of the conductors BUT, this conductor does need to go to something so Electrohome uses a bracket with a wire on it that the mounting screws go in to.

The problem I had ran into was that NTE had included additional insulators in their replacement transistor kit.  I had incorrectly assumed that more insulating is better.  The problem being that it broke electrical contact from the heatsink AND the back bracket which resulted in an open circuit, no high voltage and a dead monitor.

This is a cautionary tale.  The last 3 monitors I have not been able to fix and needed additional help on were due to improperly mounted HOT’s.  Some day I’ll learn this lesson.

Another note about the G07, the hot may appear to test as shorted because of an internal diode.  Always make sure to test from the pins to the case.  Testing between the pins looks like a short.

At The Airlock, there is a dead game in the corner called Hyperdrive.  In fact, it’s not just one but two dead games.  It appears that one side of it was dropped on it’s face.  The previous owner probably left it sitting somewhere without the seat portion attached.  If someone bumped it, it wouldn’t take much to knock it over.

When it got knocked over, I believe the monitor was broken.  This theory comes from the fact that the monitors in each side are different.  Not only that, we have an extra monitor chassis board for the side that was not knocked over.  The monitor this game uses is the Sharp Image SI-727R-DS.  The 7 must be the series, 27 is the size, R is RCA tube and DS is dual scan if I’m not mistaken.

At first, the SI-727 seems like a beautiful chassis design.  It seems like it’s everything that any arcade operator could want in an arcade monitor.  It has fairly detailed silk screening on both sides of the PCB, switchable 15K/25K frequency, a nicely made remote board and it’s very easy to remove the chassis from the frame for servicing.

Further investigation reveals some problems however.   I have a SI-727R-DS board sitting here that I have nicknamed clicky.  We tend to nickname monitors with difficult or repeating problems at the airlock.  For instance, we have squishy, which is the radar screen in pod 4…. As you can guess, that one is vertically squished just slightly.  We recapped it, touched up the solder and it was still squished.  I think the problem may be a shorted diode in the vertical drive circuit but we haven’t had time to pull it back out to check.  We also have had other such as blinky, buzzy, etc.

The SI-727 is clicky though.  If I recall correctly, it makes a clicking noise when you fire it up.  This is most likely the power supply continually trying to power up and then power down when it realizes that the horizontal output transistor is shorted.  The question it, what has shorted the transistor?

I’m really not sure yet.  This brings me to some of the problems I have experienced with the SI-727.  First off, it has some nasty trace rot.  The traces are far too happy to badly separate themselves from the PCB.  Usually this problem is indicative of using too high of a heat setting on your soldering iron but I recently upgraded my iron to an extremely bad ass Hakko FX-951.  The heat control on this iron is better than anything I’ve ever used or seen.  All that said, I think these PCB’s just weren’t made well in the first place.  In this picture, you can see the trace side of the board.  If you click on it, look very closely and you’ll see where I needed to lay some solder wick by the horizontal output transistor and use it to beef up the trace.  I’ve had to use this trick from time to time but usually it’s because a previous technician has screwed up the board.  in this case, just the act of removing the HOT tore up two of the pads.

The other problem I have with this monitor is that I cannot find a service manual and/or schematic for it.  When a problem like this arises, it can be invaluable to refer to a schematic for troubleshooting.  Sharp Image, the company that made this monitor appears to be long since out of business but I used a sneaky trick to find their old site, The Wayback Machine!  Looking through this old site however proved to be a fruitless effort.  In ALL of the archived pages I checked, old and new, the SI-727 schematic was nowhere to be found.   Some forum post mentioned checking the SI-527 manual, which I did, but that was also a fruitless effort.  All of the components seem to have different reference numbers so that’s not going to be especially helpful.

I’m confident that we will get this issue sorted out but it might be tedious without the schematic…