Nuova Bell CPU board repair.

Nuova bell was mostly know for their tranformer kits, where they adapted older used machines by putting an new playfield and a new backglass into an excisting machine , where the boards and game rom was the one from that older machine. Mostly Bally machines where used.

A more elaborated article about Nuova Bell can be found on the well know Tilt-it website here ...

The board described here is of course one of the later types made by Nuova Bell, with a complete other lay-out. Althought many caracteristics of the Bally board are to find on this board . Also two PIA's , an interrupt timer build around the NE555, the zero cross circuitry is also starting from the unregulated 43 volt .They use only half of the capacity of the memory , only 4 data bits as in the 5101 by Bally. Selection addresses of both PIA's are the same as these on the Bally board 0080 and 0090 . The start-up test indicated by 7 flashes of the on-board LED, are the same as in the Bally machines. All this gave me the opportunity to convert quickly the Bally test eprom and adapt it for this CPU board.

This is the CPU board

A short video of this COBRA machine, i did'nt have the backglass.

All boards in the head of the machine , upper left the CPU board ,upper right the solenoid/power board. Below left the lampdriver and at the right the sound board.

The display driver sits on the side panel.

Start.

To check and repair the CPU board we take it out the machine and repair it on the bench, All we need is +5 volts and the test eprom .Because the reset signal comes from the solenoid driver who is not available now on the bench, we must bring +5 volts at the upper side of resistor R19. As the connectors are very fine it best to solder at the ground and +5 run directly two wires to apply the +5 tension . The test eprom plugs in at U7.

The outer run at the left is the ground( black wire) the inner run is the +5 ( red wire) . We solder a wire from +5 ( inner run) going to R19 ( upper side) In U7 comes the test eprom.

Find the image of the test eprom here ..... To copy in a 27256 eprom.

Please check if the jumpers are the same as indicated on the schematic, I had only one CPU board and I'm not shure the game rom is always a single 27256 in socket U7. If that is the case it's shure the test eprom will work, if there is another type of game rom then it is needed to change the jumpers to use the test eprom.

Find the CPU schematic here ..............

The test is very similar as the Bally test, we first will test the both PIA's , if these are ok we check the memory.

Start .

To check if the test program runs properly we connect a test led at pin 15 of U1 ( cpu)

The test led is a normal led in series with a 1000 ohm resistor.

Connect the test led at pin 15 of U1 and the other lead at +5 volt.

Afther applying the tension on the board we reset it manually , connect pin 40 of IC 1 ( CPU) for a brief moment at ground. If all goes well both the test led and the on-board led will start blinking.

Now check with a voltmeter or logic tester that all outputs of both PIA's U9 and U10 are dancing between 0 and 5 volts ( the needle of the voltmeter will swing) . If there is an output that is not going from +5 to 0 lift that pin and check again , if its ok now the PIA is ok and there is a short on the output line , if it is still not ok the PIA is bad. This ends the output tests. ( Output pins are 2 to 17)

Memory test ,

To start the memory test push on the square push button located on the board. The led stops blinking for a very short wile and will restart . If it restart the memory test passed ok . If not the led will stay on or off, no more blinking. In this case the test still runs and tries to write and read . We can check wich signal is missing, all data signals and address signals have to be present, and also the selection signal, we need to find following values:

Memory IC is at U6.

Pin 14, 15, 16, and 17 ( only 4 data bus outputs used) = 2 volts.pulses

pin 18, select signal = 3 volts pulses

Pin 1,2,3,4,5,6,7,8,19 address bus signals = 2 volts pulses

pin 24 = +5 volts steady.

pin 22 1,5 volts pulses.

If the values are correct the memory IC is bad, if there is a signal missing check with the schematic where it has to come from and follow the signal "upstream" to find out where it get lost.

Test does not run at all.

When the test does not run at all, meaning that the LED connected at pin 15 of U1 does not blink afther the manual reset, we will remove the useless test eprom , without any program present restart the board with a manual reset . The following basic signals must be present now: On the CPU U1 pins 2,3,4 and 7 = 5 volts, Pin 5 = 3 volts. All address and data pins must pulse, you will find values between 1,5 and 3,5 volts. The data and address bus pins are from 9 to 33 ( except pin 21 wich is the 0 volt) On the selection pin of the eprom U7 ( socket ) there must be about 4 volts ( pulses) . If any of the signals is missing , as always bend upards that pin,measure again , and if the signal is there you have a short somewhere on that line , if one of the data or address signals is still missing the CPU IC is bad , the same if there are no signals at all or if the clock signal is missing at pin 38/39.

Last test.

When, the board is working with the test eprom we can preform a test with the game rom. Install the game rom and do a manual reset , the board should boot and give 6 flashes , the 7the flash is missing because there is no 43 volt applied , wich normally comes from the solenoid/power board. If you want to see all 7 flashes , lift pin 18 of U9 and make a temporally connection with pin 40 of U10. This way you will have all 7 flashes as normal, and afther that the on board LED will steady and faintly glow.

Here the connection between pin 18 U9 and pin 40 of U10.( red wire).

The tests included in the game rom are similar of these of Bally. You can find the meaning of the several flashes in Bally articles . I recommend the Bally repair pages at marvin3m.com .

The solenoid&power board.

On the board we find a " black box" this box contains the 5 volt regulator and the reset cirquitry. As the box is completely sealed , there is a problem when he is bad.. Needless to search a spare part.

The solenoid power board with the famous black-box.

Completely sealed with epoxy. Signs of melting .....

As you can see mine was bad, traces of melted material on the board .

The 5 volt regulator was replaced by a LM323 on a cooler block, with extra mini-fan.I added a extra fuse on the 5 volt output. You need to drill some extra holes to mount the LM323, the wires for the fuse and ventilator are passing throught excisting holes.

The reset cirquitry is replaced by a special reset IC, find the datasheet here ...... The IC looks like a small transistor, and is connected at 5 volts and the thirt lead is the output wich gives +5 volt afther a short delay at power up.. The IC is placed near R70 and R1 where two runs , the 0 and the +5 are close , so all what there is to do is drill two fine holes and fix the IC ,the thirt lead is connected at pin 22 of the MPUconnector. There are several type of special made reset IC's you can use another type as well as this DS1811.

Find here a part of the solenoid -power board schematic and how to insert the new regulator and the reset IC. The red parts are the adaptions , the rest is the original schematic.

Find the full solenoid/power board schematic here ....