Leon Borre Atari Second Generation Repair
Atari pinball test program
I own no Atari pinball myself, as a matter fact I never seen an Atari pinball. But due to demand from a few German pinball fans, I made this test program. Because of the different electronic design of Atari pinballs, they seemed to be more difficult to repair. Thanks to Frank Oeffelken who sent me the schematics as well as a complete cpu and I/O board used to perform this study and the preliminary testing. Only a few models of this style Atari pinball were made. The test program and the cpu board that this test program will run on is only used in HERCULES and SUPERMAN. Perhaps the same cpu is used in 4X4, Road Runner, and Neutron Star, but these games were only prototypes, and the production runs were very, very low. The other models, Time 2000, Middle Earth, Airborne, Space Riders and Atarians, have another type of "all-in-one" board. Atari, like pinballs made by Bally and Williams from the same period, use the 6800 cpu chip. However, Atari does not use the common I/O (input / output) peripheral chip 6820 / 6821, which was specially designed by Motorola to go with the 6800 to provide a versatile and simple I/O instrument. Because of the lack of this chip, the Atari pinballs have a more complicated way of dealing I/O matters. All I/O is specified selections and latches which maintain the selection. The test program I developed will control these selection signals, and make them go high (5 volt) and low (0 volt) in rhythm. This is the same process I did with the output signals of the classic 6820/6821 on a Bally or Williams cpu boards. Furthermore, I test the memory chips and some specific circuits as there are the "watchdog" and hardware "interrupt" circuitry.
On an Atari cpu board there are 4 LEDs. I use these to differentiate the results of each of the tests performed, so we do not have to count the number of "flashes" to determine which RAM or circuit is faulty. I still use a simple LED to control the good working part of the test program. The LED is to be connected to address line 14 instead of the usual address line 6. To control the “dancing” selection signals, it will be necessary to use a logic probe. For those who do not have a logic probe, a simple and good working DIY example can be found on this site. It is also possible to check the different selection signals with a voltmeter. However, the voltmeter must have a scale from 0 to 1 volt (full scale), because the impulse trains are very small. The deviation of the voltmeter needle is very good visual aid.
The test program
The first section of the test program will test the selection signals. These signals will be activated 128 times, then a period when they are not activated, and so on, and so on. This results in a pulse train, and this pulstrain is easier to observe and to follow than a single selection pulse every few microseconds. At the same time constantly change the data send along with the selection. That way all possible values are sent to the latches, and the resulting outputs can be followed over to the I/O board. If the selections are found ok, the tests continue with the memory test, the interrupt test, and the "watchdog" test. For each test that is determined all right, one of the LEDs (L1 - L4) on the cpu board will be activated. All these things and how to proceed are explained below in the user guide, as well as what to do if you find some things that don’t work at all.
The CPU Board
On the lower left of the CPU board is the power connector. Three wires need to be connected for us to use the test ROM. The red wire is +5vdc, yellow is +12vdc, and black is ground. The test EPROM is located on the right (with the white label). The red arrow points to the test point marked "Watchdogkill". This test point is needed during tests. Above and to the right, is a round grayish button. This is the reset button. To the right of this button are the 4 CPU LEDs. These LEDs will display information during the "memory test".
The board is to connected at 5 volt and 12 volt. You find the connector at the left side of the board. The male pins on which you need to connect these tensions are the same as the male pins of a power connection from a hard disk used in a PC (personal computer). So if you have an old PC on hand, you can find the right female pin there. Ground comes on pin 1, +5 volt on pin 2, and +12 volt on pin 3. Use colored leads to differentiate between the different voltages!!! Connect a control LED between address line 14 (pin 24 of chip N6) and ground. As always, the control LED consists of a standard LED in series with a 1.2Kohm resistor. First use figure out which side goes to address line 14 and which side goes to ground. To start the test just place the 2716 test EPROM in position J7.
Classic connector found in old PCs. Use the female pins to connect the different tensions to the CPU board's connector. They fit perfectly!
The test program is available for download here
You can burn it onto a 2716 EPROM. In case you don't have an EPROM programmer, ask a friend or other pinball fan.
User Guide
With test EPROM in place, and the tensions applied, the control LED should blink in rhythm. This rhythm is rather slow - "off” for 2 seconds and “on” for 6 seconds. If the 4 LEDs on the board also blink, there is no great problem with your cpu board! We now can control the different selection signals. These signals are on the chips H4 and E4. On the output pins of chip H4 (pin 1, pin 2, pin 3, pin 4, pin 5, pin 6 and pin 7), you will find “dancing” signals. You need a logic probe to see these signals. ATTENTION: if you use a voltmeter, you should connect the positive lead to 5 volt and use the negative lead to check the selection outputs!!! The needle will move about 1/10th on the 0 to 1 volt scale, except for pin 4 of H4 and pin 7 of E4, where you should see 1 volt. Pin 9 of H4 is the selection of the test EPROM, so it will be selected on all the time. The same selection signal results should be seen on chip E4 (pin 1, pin 2, pin 3, pin 4, pin 5, pin 6 and pin 7). Pin 9 is the exception here. It will be “intack” (ed. note: not certain how to translate this), and controlled during the memory test. It is the interrupt selection, and cannot be activated during this general test.
If one or more of these selection signals are not ok, you have found a problem. The first thing to do is to ‘liberate’, (ed. note: again, not certain how to translate this other than possibly 'isolate'), the missing output temporarily. To do this, lift the output pin or sever the trace connected to it. If the output is still missing, the chip (E4 or H4) is the cause. If the output is now present, then the output is grounded somewhere. The process of elimination by cutting traces or lifting chip legs will help you easily find and replace the chip which is causing the grounding.
In the case where the output "IOWR” is missing at H4 pin 4, all outputs at chip E4 will be missing too. So if this happening, first repair the missing IOWR before continuing onto chip E4 outputs. In another instance where the control LED is blinking, but you do not find any outputs on E4 or H4, the only possibility left is the input ports of H4. These are L5 and P5. The worst case is when the control LED doesn’t blink at all. In that case, we have to repair some fundamental circuitry of the CPU chip and buffers. Some fundamental circuitry is needed to make the test program work.
No control LED blinking
The first thing to look at is the cpu chip 6800 and its signals. To do this remove all roms or eproms included the test eprom, so sockets K7, J7, L7 and M7 must be empty!! We first will look at some pins of N6 ( cpu chip) pin 2 = 5 volts, pin 3= 2 volts , pin 4 = 0,8 volts and when you push on the reset button ( black button just above the 4 leds) your voltmeter needle will jump up to 2,5 volts , pin 5 = 4 volts , pin 6 = 5 volts ,pin 7 = 0 volt, pin 36/37= 3 volts, pin 40 = 5 volts, if there is something wrong look at the circuit from where the missing signals comes , this is always only one or two chips in the clock circuit the reset circuit or the power reset.. In case you see the pin 40 not at a stable 5 volt , but with a "changing " signal , then connect the TP " watchdogkill" temporally to ground. If this helps leave the connection and continue, we will handle this " watchdog" reset with an appropriated test under " memory test" further down this pages. If the signals are ok then control the address and data lines. On the data lines (pin 26 to 33 ) you find ~1,5 volts, on the adreslines ( 9 to 25 except 21 ground) you find ~3 volts. Also look at the buffers of this signals L6 for the data and N7 for the addressline ( A0 to A7) generally if missing it will be the signal after the buffer. This does not mean the buffer chip is bad, it can be a grounding of the signal after the buffer, so again free the buffer output to see if the buffer is ok or not. Missing or bad value of a data or address value is caused by a grounding or bad chip connected at that line.. Again elimination by lifting of pins or by temporally cutting of runs will bring you to a solution. After this the leds on your cpu board will all blink in rythm, and we proceed with the memory test.
Memory test
The leds on your cpu are blinking now, to start the memory test we have to ground the TP " watchdogkill" temporally. We start the memorytest up via the NMI ( pin 6) on the cpu. Use a grounded lead and touch for a brief moment pin 6 of N6 . The 4 leds on the cpu will go off and if all is well go on again after a short moment. The first led indicates that the “ battery ram” (H6) is ok the second indicates that the set of two “ normal” rams are good (K6&J6), these two rams are tested as one, so if anything is wrong with one or another switch them one by one with the “ battery ram” to find out witch is causing the default. Led 3 indicate that the interrupt circuit is ok, and the 4th. led indicates that the “watchdog” circuit is ok. The 4 leds should remain lighted constantly; if they go blinking again the “watchdog” reset circuit is not ok.
The cpu prepared for "memory test" the temporally connection between " watchdogkill" and ground is made.
So if something is wrong, none, or only one, two or tree leds will go on.
What to do if no led turn on;
This means that the ram in H6 is not working, first replace this ram with a 2101 that you find in K6 or J6, these are pin compatible and suited for the test propose, in real game play you need a 5101 because the 2101 has an higher power consumption and drain your battery in tree days by this higher power consumption. After the change you restart the memory test ( ground pin 6 of N6 again a brief moment) Another good thing of the test is that as long as the test reads “ ram not ok” it will continue to test that same ram and we can now control the signals coming on the ram chip. This gives us plenty of time to check these signals on the ram . I did this for you and you have to find these results:
As the test is turning around on the bad ram, the signals you find are stable, aboutb 50% of the working voltage and easy to measure with a voltmeter,
Pin 1 , 2, 3, 4, 5, all these are 2.5 volts
Pin 6 and 7 about 3 to 3.5 volts
Pin 17, 19, 20 = 4 volts
Pin 18 and 21 = 2 volts
Pin 8 is ground and pin 22 is 5 volts.
If only one led is ‘on’ the fault is with the rams at K6 or J6 . Try them one by one in socket H6, to see witch is the bad one, if both are found ‘good’ test the signals on these rams you have to find the same values as for the " battery backed ram" ( H6)
If only two led are ‘on’ the interrupt circuit is faulty. In that case the cpu will go into a ‘ wait’ state, and all activity will stop. .. To solve this problem it is needed to repair the interrupt circuit, this circuit is build around 3 chips, the first one is E4 ( output “ intack” pin 9) as we have already controlled ALL of his outputs, it is probably not this chip that will cause troubles. Over to number two and tree, L5 and M1. The only thing we can do in a first stage is to control the connections between the tree chips and look for cuts or shorts on the runs. The signal “ intack” starts at pin 9 of E4 to pin1 of L5 comes out of L5 at pin 3 to pin 13 of M1 and comes out again at pin 8. You cannot follow the signal dynamically because the cpu is “halted” …. That is why I indicate the way the signal flows and advise to look at the connections. If you don’t find anything there, you have to replace L5 or/and M1and in the last stage E4.
Test watchdog reset.
Together with led 3, led 4 will go ‘on’.This is the control of the circuit " watchdog" Now we MUST remove the temporally connection between TP " watchdogkill" and ground, the 4 leds have to stay "on", "watchdog is dynamicly resetted by the program ( instead of by an external connection.) this is the end of the test. If the 4 leds start blinking again there is something wrong… The watchdog made a reset and the test program restarts with the normal first stage of the test program. This gives us now the opportunity to test this watchdog circuit. First we connect the test point “ watchdog kill “ temporally to ground, now the normal test routine will run, as the “watchdog” is out of service , we follow the signal..The circuit is made off, E4, L5, F6, N5, M2, . We start at pin9 of L5 , use the logic probe, from there to pin 8 L5,the signal now comes to pin 13 of F6, pin 12 of F6, pin 3 of M5, pin1 of M5, pin 1 of N5, pin2 of N5 pin 12 of M2 . if the signal flow is interrupted somewhere on this road the chip where it comes “in” but not comes “ out is faulty.
Test watchdog set
The last thing to control is " watchdog set " signal. Undo the connection between TP " watchdogkill" and ground, start the memory test in the normal way. The 4 leds MUST blink. If they stay "on" permanently the set circuit is bad. To repair this follow this procedure.
Remove ram chip K6 , start the memory test , WITHOUT the connection TP "watchdogkill " to ground. The signal "watchdog set" will appear on pin 14 of R2, follow this signal with the logic probe along the foillowing points, L2 pin 1, L2 pin 8, M2 pin 1, M2 pin 6 , M2 pin 13 , there it resets M2 that will cuase a complete reset. If the signal is missing somewhere , the chip where it goes "in" and do not come "out" is bad. Whenever it reaches M2 at pin 13 , and the leds are not blinking , M2 itself is broken.
If all testing is ok now the cpu board will work fine, and we can follow the signals to and on the I/O board now.
The I/O board.
If you have some doubt on your I/O board we can check that to, using the test eprom. All signals towards the I/O board use connector J4. But before the signals leave the cpu they pass true extra chips to give them more power. It is good to check at J4 if the signals have the right strenght as they leave the cpu board. So we check the signals on J4, and take the I/O board on the bench afther this final check.. We find at J4;
Pin
If there are missing or weak signals, look at the schematic wich of 4 chips it comes from and replace that one.
To repair of I/O board Atari……………..