notANON

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…

I’ve been spending a lot of my free time lately helping the guys over at The Airlock bring some of their newly acquired arcade games back up to good working order. The majority of the time, monitors are the problem area with these games.

One of the latest ones I fixed was Donkey Kong. It’s an original dedicated Nintendo cabinet from the early 80′s. One of the better looking design schemes out there. In the cabinet is the original Sanyo EZ 20 monitor mounted up on it’s side which is important to note for later…

This monitor had a weird problem. It lost all ability to hold the picture horizontally which appeared as vertical static since the monitor is mounted sideways. The weird thing though was that when you first turned it on, it was fine but then if you rebooted it, this condition existed. Sometimes it went into this condition after many hours of play though as well.p

With monitors, my usual starting point is caps. The electrolytic capacitors in this monitor appeared to be 30+ year old originals. CRT monitors are notoriously hard on caps. These games were only designed to last 2-3 years at the most since in the golden era of arcade, it was unfathomable that anyone would care about a game past that point.

Back to Donkey Kong though. Of course I started with the caps. I figured I had fixed it when I fired it back up to a perfectly clear picture. I turned it off to finish reassembling the monitor and when we turned it on to retest, we found our familiar squiggles.

Kelly, one of the guys at The Airlock, thought this may be a logic board problem in the video circuitry since it was a problem we were unfamiliar with in our experience of fixing monitors. After 20 feet of solder later and many questionable joints fixed on the logic board the problem still remained however.

Enter the freeze spray

Since the problem appeared only after the game warmed up, I figured that we may have a chance to pinpoint the faulty component with the old freeze trick. I grabbed a can of r134a that is on hand there and the little red straw and started blasting while someone watched the screen for me. It didn’t take long since the screen went back to a perfect picture practically on my first spray.

I power cycled the system and luckily the problem immediately reoccurred. We repeated this process, each time being more precise with the can of spray until we finally pinpointed the problem component, a 1/4w 1k resistor. Swapping that out fixed the problem and it’s been rock-solid ever since.

It was interesting to me that a resistor became heat sensitive. I was originally expecting it to be a solder joint, a cap(but they were all replaced) or a heat-sensitive IC perhaps.