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The video chains are 8 bits wide each, but the 9316s(74161s) are only 4 bits wide, so you need 2 for each chain. If you look at the schematics, [M1] and [N1] make up the vertical chain. The bits are backwards from the way you would normally write them, so I should actually say [M1] handles the low-order bits 1V', 2V', 4V', 8V' and [N1] handles the high-order bits 16V', 32V', 64V', 128V'. Since these counters are all synchronous and share the clock, the CET/CEP inputs are used to enable counting, and the TC (terminal count) output from the lower-order chip enables the CE input of the next. The problem with our board is that [N1] kept counting, even though the CEP input on pin 7 was low.

@@bytemind1633 I think all arcade games use 8 Bits wide Video Chains for the H&V sync signals?. The H&V Counter Chips often go bad because they are overworked they are working all the time. I'm guess the N1 counters chips CE input stage got damaged which make the High Order Bits counter chip FREE RUNNING constantly?

Most video games have more. Even pong had 9 bits per chain. Since the design bonus was low chip count, Woznick traded a bit of video signal fidelity here. Breakout graphics are not "fine" (well, pong not either), and the monitor could handle it, so it works. Yes, the [N1] ignored the CE input and just kept running - hence no proper vertical separation. In the 3rd video you can see the outputs running faster than the high-order horizontal counter as well. The vertical portion of the SYNC signal (VSYNC) is generated by the high-order vertical counter in [N1], plus 8V' so I'm still surprised the monitors were able to show anything. Could force the issue again to see, but I think we'll just move on.

@@bytemind1633 What do you mean by "per chain" ? Are you saying that the video output signal going to the arcade monitor has 8 bits of vertical signals and 8 bits of horizontal signals? I thought that these are multiplexed before it leaves the game board and the arcade monitor uses a Sync Separate IC chip to separate the V&H signals decoding them

9-bits for both vertical and horizontal counters. You are correct, all video stuff gets merged into one composite signal that's sent to the monitor. Interesting that this composite signal coming off pin [V] is just a plain wire in the harness and not coax (and runs next to both 16.5v A/C and 110V A/C signals. If I put my hand on the harness, the video integrity improves. I'll probably coax this line to improve it a tad.

"Boundary" signals, in this instance, are the left and right bars at the edge of the screen (and also the top) - see diagram 3-2 on page 6 of the manual. You'll see this as LH SIDE, RH SIDE, and TOP BOUND. Naturally in an AND gate, both inputs must be high for the output to turn on. CR9 cathode is low until 128V+64V+16V+8V+4V are on (we'll draw this out later). !HSYNC applied to CR10 cathode forces the CR9/CR10 anode pair off, keeping the LH SIDE and RH SIDE signals off. Also, since the monitor is rotated 90 degrees clockwise, LH, RH and TOP are from a play view perspective. The V and H signals are from the normal monitor perspective. Other interesting signal names: PSYNC=Paddle, BSYNC=Ball, BPHIT=Ball/Paddle Hit, BTBHIT=Ball/Top Boundary Hit. The flip-flops in the center of sheet 1 control ball motion direction. For example, D5a controls direction of the ball towards the top or paddle (they call this x-direction). You can see this flip-flop set when the ball hits the paddle (BALL DISPLAY + PSYNC), and reset when it hits the top (BSYNC + TOP BOUND). You would think they would use BSYNC for both but...

Very kind.

@@bytemind1633 Thank you for your reply ! If you are interested in the nostalgic game culture of Japan, please subscribe to my channel !

Thanks for the comment, John. Yes, each director was basically a 3158 with different functional packaging and different microcode. Both have 6 channels (2 byte multiplexer and 4 block multiplexer - except the optional director 3 has just 4 block multiplexer - max 16). I only worked on a few '158s (~10) and one of the cool things was a 60 to 400 Hz converter in the bottom of frame 3 (instead of requiring a motor-generator set). The frequency makes it easier to filter. Did you have a chance to take a look at the link I put in the description? Some interesting stuff in there too. Paul

@@bytemind1633 I did. Thank you!