New Life Games LLC
**Video Poker, Keno, Slots, 21** Gaming machines => CEI and Cal Omega Video Poker Games => Topic started by: rokgpsman on November 23, 2015, 08:52:53 PM
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Dave (aka The Fatman)-
This is a description of the audio/sound circuit on a Cal Omega/CEI machine based on the few drawings I have. I’ve used the 904 mpu board and 911 motherboard for this, other versions of boards are somewhat similar but could have different designator names for component parts and connectors. Keep this in mind, your machine can be different. If anyone sees any errors in this please let me know and I will get it corrected. I'm not even close to being familiar with these models of machines, but maybe this will help anyone working on a sound problem.
On a machine that has no sound you should first verify that the speaker and its wiring are ok, or if the mpu board is causing the sound problem. If you do have some sound, even if it is noisy or weak, at least you know the speaker is working. If you have one available you can swap in another mpu to prove if your mpu board is good or bad. You can use a meter to check the speaker, it should measure a low resistance of just a few ohms (8 ohms is common). When setting a meter to do a resistance or continuity test it will have a low voltage on the meter leads, this is how it does the test. This voltage is sometimes enough to cause the speaker to “pop†slightly when you touch the meter leads to the speaker wires or terminals. This popping sound will tell you that the speaker is likely ok but measuring with a meter is better. You will also want to verify that both speaker wires are intact from the speaker to the mpu board audio output, thru any intervening connectors. If you determine that the mpu is bad then there is some info below to help you with that.
The audio signal goes from the mpu board into motherboard connector J102, pins 22 and 23. From there it is routed to the motherboard audio connector J304 pins 1 and 5 which connect to the speaker wires. The audio signal also goes to the motherboard TV Video J301 connector at pins 1 and 2. I suppose this is for display monitors that have audio capability.
On the mpu the sound is created by the sound chip U77, a 28 pin ic usually with the marking “SOUND†on top. This ic typically has a part number which includes “AY3-8912â€, it is powered by 5vdc. This sound chip is under the control of the game software which sends commands to it when a sound is to be created. On some mpu boards there is a dipswitch called SW3 that is located near the sound chip U77. I don’t have any information about what options it might control and it may only be implemented in certain game software. On the 904 mpu schematic that I have dipswitch SW3 is shown having all positions set to OFF (OPEN). The low-level sound output of U77 is connected by capacitor C30 to a pre-amp called U78, which is a two-stage audio amp powered by 12vdc on U78 pin 8. U78 also does some filtering to the audio signal.
The audio signal leaves U78 on pin 7 and is connected by capacitor C36 to opto-isolater U55. This is done to isolate the following circuit U79 from the preceding circuit as a safety design. U55 passes the audio signal along to U79 by an indirect means, using the photo electronic characteristics of U55. This way there is no direct connection between the 2 circuits. The input half of U55 is powered by 5vdc, the output half is powered by a special 12vdc created by CR8 and C8 just for the last stage of the audio output circuit.
The audio signal leaves U55 on pin 8 and is connected to the volume control R118. The wiper (pickoff arm) of R118 connects the audio signal to capacitor C37 which sends it to the input of main audio amp U79. U79 is powered by the same special 12vdc as mentioned earlier, that voltage is applied to U79 pin 14. The fully amplified audio signal exits U79 on pin 8 and is connected to capacitor C39. C39 sends the audio signal to mpu connector J102 pin 22 on the motherboard. J102 pin 22 is the audio high side, J102 pin 23 is the audio low side or return line. From there it is routed to the motherboard speaker connector J304.