By Jess Askey 3/19/96
The first step in fixing any problem is to know what the problem (or symptom)actually is. This is your best guide to solving the problem and fixing the monitor.
Does the monitor work at all?
Is the problem in both the X and Y axis?
Is the problem intermittent?
These are some of the questions to ask yourself, knowing exacty what the problem is can save you lots of time and frustration. So, now before you move on, read the theory of operation for the monitor in question from the manual or from the Vector Page. Understand each section and what its purpose is in the big picture. I don't know quite how to do this next part so just skip over the part that do not apply to your situation.
MONITOR DEAD - No noise, no glowing inside the neck of the tube: This is probably an external problem. I say this because the filament inside of the neck( which is used to heat up and exite the free electrons used to create the electron beam) is powered directly of the 25VAC before the monitor fuses. Most likely D108 and R107(if it isn't crushed) are good. So that means you should check your fuses on the transformer block and replace them, sometimes they just go!!?? Another thing that causes this problem is burnt connections at the fuse block, I have seen many transformer blocks with burnt tabs on the fuses. PREVENTIVE MAINTINENCE: Check your slip-on fuse connections and snug them up with some needle nose pliers, remember to turn off the power!!
BLOWN FUSES - This will cover most everybodys problem since XY's love to (or missing eat up those 5 and 3 amp Slow-Blow fuses. If a fuse is quadrants) take it out and make sure that it was a SLOW BLOW fuse. FAST ACTING fuses will not work and if you put a higher rating fuse in, it will not protect your monitor. Yes its true however that if you put in a 30 amp fuse you will be shown where the problem is by some nice fireworks and lots of smoke but you don't want to waste a perfectly repairable monitor! Anyway back to the topic, just remember to put in the right value fuses. QUICK TIP: Since everything is slow blow, you can usually see the fuse start to get red hot before it blows. so if your quick enough on the power switch you can turn off the game and save a fuse and still know that the monitor still needs some work!
MOST COMMON PROBLEM: One of the deflection transistors or power supply regulators has shorted. The best way to check this is to get yourself a ohmmeter and measure from each transistor case to the monitor chassis (GND). None of them should be less than 10,000 ohms. You have to unplug the transistor connectors to the board (ex..P600,P700,P100 on Well/Gardner) or you will get false readings. If you find a short from the case to ground, that transistor is bad, use an exact replacement. When putting in the new transistor be sure to use the mica insulator and some heat sink compound. Or for an easier installation use the silicon type insulators, they don't need heatsink compound. PREVENTATIVE MAINTENENCE: Moving your deflection and power transistors off the chassis and on to a large (real) heatsink, will keep your monitor running cooler and longer. Williams power supply sinks hold 2 transistors per and are relatively easy to find. Sega XY monitor use two nice heatsinks mounted together with a fan blowing straight through for optimum cooling. I sell kits that are prewired with all 6 transistors and a fan that will mount nicely anywhere inside the cabinet. E-mail for details! After you have replaced all the bad transistors check for shorts again, plug it all back together and try the smoke test. Watch the fuses so you can turn off power if they start to glow. Look at the picture and see if your doing okay, if not measure the transistor cases again for a short and then move on to the next section.
NORMAL MONITOR OPERATION: This is just for reference so you can narrow down your search for the problem your monitor is having.
SPOT KILLER -This is shown by the red LED on the deflection board. It Should turn off about 1 second after you turn on the game. When it is on, the deflection board is not deflecting the beam to draw anything and the raster is in the center of the screen. The edgy oscillation sound you hear during normal operation is the deflection.
HIGH VOLTAGE - It is difficult to tell if you have high voltage or not, you can't hear the oscillator as in normal raster monitors because the XY high voltage oscillator is well above hearing range at 30,000 hertz. One way to tell if you have any high voltage is to turn up the screen brightness control and see if the picture "glows" or any other bright objects on the screen. Another way is to touch the screen and feel if there is any static however you can really zap yourself if it is dry outside. The best way is to measure the anode voltage with a high voltage probe or measure the ' screen voltage on pin 9 of the picture tube, it should be 544V. One more way is to look at the spot killer, if the LED is off and you have no picture, you most likly have no high voltage either. If you are now certain after all these checks that you have no high voltage the first thing to do is to see if your high voltage unit is getting the +28V and -28V it needs to operate correctly. Check on the input plug for these voltages in reference to ground. If they are there the problem is either in the High Voltage unit or your picture tube is bad. If the voltages are not there then your problem is in the power supply and not the high voltage unit. If your problem is in the high voltage unit, there are too many possible components to tell exactly which part is bad. You can generally trace the problem to a specific area by checking the voltages listed on the schematic against yours. Generally Capacitors are the culprits in the high voltage supply but when they go they will ususally take with them a couple transistors resistors and/or diodes. Cold solder joints also can cause malfunctions and are very easy to repair, they look like pitted metal with cracks in them, resolder any that don't look shiny and/or smooth. There aren't that many parts in a high voltage unit luckily so you can but get well kits that will generally do the job. Kits will be available through me in a couple of months.
POWER SUPPLY - The XY power supply is very simple. Usually Q102 or Q103 will go after repeated deflection transistor failures (it stresses them out). Additionally the heat sink compound will dry out and these babies will start to get really hot. Relocating them an external heatsink will improve their life drastically. But if your monitor is already dead then that is just wishful thinking. The power transistors will rarely short but if they do your monitor will probably still work, some other section will fail soon since the nice +/-24V is now somewhere aroun 38V. Check both power transistors as explained in the previous section and replace any shorted and/or open transistors. The most common problem in this section is shorted Zener diodes ZD100 or ZD101. If they are shorted you will not have any output voltage from that half of the supply.
That will sum it all up for now. I will add more to this as I get more time and some feedback. Send me your problems with the associated solution and I will post them in here. Thanks Good Luck. You can also E-Mail Me.