This flowchart is excerpted from a photocopy of a photocopy (of a...) which has no visible attribution or copyright. It appears to be from the Star*Tech Journal but I don't know for sure and the guy who sent it to me doesn't know where it came from.
Most problems in the Tempest display can be found by following the procedure shown in the chart below.
CAUTION: When replacing the transistors mounted on the chassis, make sure the pins do not short to the chassis. If the chart procedures do not solve your problem, call Atari Field Service [NOTE: They will be of little help nowadays :>].
[NOTE: I have taken considerable liberty in restructuring the flow and rewriting the text in order to be more clear than the original chart and to better fit in 80 column text format. I have added a couple of things, too.]
No picture and... +--------YES---- 5 amp fuse (F100 or F101)----NO-------+ | on Deflection PCB blows? | \|/ \|/ Cannot get/keep +/- 28 Volts. Turn up brightness and contrast controls Disconnect P600, P700, and<--------+ on HV PCB. Is there a dot in the center P100. Power up monitor. | of the screen?-----------------+ | | | +-------+ | \|/ | NO | | | YES | Fuse still blows?-------NO-------+ | \|/ \|/ | \|/ | | | Is there +/- 28V on | Is there 180V on YES | | | on pins 1/8 of P900? | pin 5 of P900? \|/ | | | | | | | Replace the following components | | NO | YES | +-----+ YES | NO if shorted: D100, D101, D102, | | | | | D103, C100, and C101 | +--------+ +----------------------+ | | | +-----------------------+ \|/ \|/ Change or make sure C901 and C902 are Check for Q102/3 collector short to 100uF at 50 volts. Check for a leaky chassis. Replace the following compo- C905. If C905 is bad, also check or nents if defective: Q100, Q101, D104, replace Q900, Q901, Q902, Q903. Is D105, ZD100, ZD101, Q102, and Q103. there 180 volts on pin 5 of P900 now?-+ | | | \|/ NO | YES | Connect P100 and power up. Is | | the +/- 28V on pins 4/5 of P100 Check resistors R100, | | OK now?--+--------------NO------------->R101, R102, and R103 | | | for open circuits. | | YES | | | | \|/ +------------+ | | Replace the following components | \|/ | if defective: Q603, Q605, Q606,<---+ Double-check the above transistors. | Q703, Q705, Q706. Also look for burnt (open or shorted) | | resistors R903, R904, R905, R906, or | \|/ R907. | | Connect P600 and P700 and power | | up. Picture now?-------YES--------+---------------------+--------------------+ | | NO | | Is picture "blooming" (does the image \|/ +--->appear as though being viewed through Check remaining transistors | a magnifying glass)? | in the X and Y amplifiers. | | | Then make sure the following-------+ NO | YES | resistors are not open: R702, \|/ \|/ R703, R711, R712, R602, R603, >END<----Replace ZD902 on HV PCB. R611, and R612. / \====================STOP=====================
Let's finish off with a troubleshooting guide broken down by symptoms. Much of the rest of this section is a transcription of repair notes from a Wells-Gardner technician. Just because your symptom matches something in here is no guarantee that what I/he found wrong is the same thing that is wrong with your board, but it's a good place to start. Most of the problems he listed in his notes were due to manufacturing defects or incompetent repair work. Obviously, if your monitor was working OK and then simply stopped, those things are not likely be your problem. If you have seen any problems that are not listed in this section, please contact me and I will add them.
Display "implodes" during intermission screen between player one and player two and sometimes on the "figure 8" levels (Tempest machines only): I thought I knew what was causing this but upon further evaluation, my solution didn't make sense (although it did work for me the only time I had this problem). Until I get another board to fix that has this problem, I only have general advice on how to avoid the problem. Adjust your game board and "shrink" the Y deflection some and this should help. There are 2 sets of ROMs for this game and the "compact" ROM set (only half the ROM sockets are used) is slightly different (the intermission screen has some other stuff such as the copyright and credits information at the bottom of the screen which "balances" it out) so the spot killer won't get confused and decide that the bottom half of the screen is wiped out. These PCBs do not normally experience this difficulty.
Check the fuses first. If they are OK, then check the 6 transistors mounted on the chassis as described earlier. If you find at least 2 of the deflection ones or 1 of the power ones bad, then that is definitely tripping the spot killer. A good trick to figure out where the problem exists is to turn your brightness up all the way and see what your picture looks like. The spot killer doesn't turn the Z signal all the way off so if you turn the brightness all the way up, you should be able to see a very faint picture. Based on what the picture looks like, you can decide which half of the circuit is causing the problem (either the X or Y portion). If you know it is a problem on your deflection board (i.e. swapping another board in makes the monitor work) then check R808 (X) and R809 (Y) to make sure they are not open. These resistors allows current to flow to the spot killer circuitry and if they open then the spot killer thinks something has happened to the amplifier circuitry so it kicks on. You can tell if this is your problem by turning the brightness on all the way; if you see a complete picture, then this may be your problem. If all this is OK then you probably have a game board problem, particularly if you are unable to "play" the game (see the credit lights blink after you punch up credits and hear the game sounds after you push start).
The problem is most likely Q603. Occasionally you will see Q603 (Q703), or Q604 (Q704) go bad. If one does, be sure to check the resistors and diodes around it, particularly R611 (R711), R612 (R712), and D602 (D702). A common modern day replacement for MPSU57 (Q603/Q703) is NTE189 and the part for MPSU07 (Q604/Q704) is NTE188. These should be greased where they touch the heat sink (like the chassis transistors) to improve heat dissipation. If you are having trouble with these failing, you might want to beef them up by using TO-202 package upgrades to NTE50 (MPSU57) and NTE49 (MPSU07).
Jeff Young from World Wide Distributors in Grand Rapids, MI reported some words of caution about these resistors on Page 3 of the November 1982 issue of the Star*Tech Journal:
The resistor is burning up because of runaway current from the HV unit. You can confirm this by replacing R101 and testing the deflection board in a known good monitor (or by putting a known good HV unit in the monitor that is acting up); if R101 doesn't burn up then you know the HV unit is the culprit. Whenever this has happened to me, R903 in the HV unit has been the cause. It will sometimes short and this causes so much current to flow to the deflection board that the puny 15 Ohm resistor burns up. If this goes on for too long, Q101 may fail or occasionally R901 will burn up to an open circuit.
I have seen this several times and the problem has always been a bad ZD101. Much of the time this causes R101/Q101 to fry and spot killer comes on.
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