Another Space Invaders sound issue

[N24005]

The 174s are labeled 2 and 7. The 175 is #12.

I don't see any control signals on them except Port 4 on Pin9 (Which is high) and bar reset on pin1 which is signal high.

One of the 174s is socketed

No, I don't think port 4 (high) is tied to bar reset (signal high - ie low light is also lit)

Not sure I answered you questions, you lost me

 

[wugly]

read directions on probe. high and low do not mean that is what the signal it is reading is doing. there is a light labled pulse and if that is flashing then high or low tells you how fast the signal is changing. if its not pulsing then high and low tells you the logic state. which is pulsing port 4 or bar reset hard to tell from how you wrote the answer

 

[wugly]

had more time to digest what you said

Looking at the 74-174s and 74-175 where D0-D7 interface with DS0-DSF…

All data lines have activity, however, all DS lines are solid low.

Pin 9 (clock - port 4) are all high, while pins 1 (^reset) all have signal high.

Looking at the data sheet, if the clock is stuck high or low, then the input has no effect on the output. Hmmmmm

Looks like E3-7 (7442 output 6) drives that from pins 12-15. Pin 12 is always high so 7 will always be high. (If this noob is reading it correctly)

Should Port 4 be high? This is also tied to D2-1 and E2-1 (clears counters)

Thanks!

Attachments

according to you all data input lines have data. and all data output is stuck low but you have some data output that is connected to input data that you say is pulsing but you said the output that the input is tied to is stuck low. am wondering if you have assumed how a probe works and do not realize its intricacies.

 

[N24005]

Yes, I freely admit that I'm a noob. I am beginning to wonder if my logic probe is faulty because no matter what I probe, I do not get a blink on the pulse light. (No, it is not set on men). I even tried on the clk. So let's put that aside for a minute and break out the scope which I am also a noob with…

Keep in mind that I am running the v1.3 test rom. The Midway manual page 39 talks about the sense line getting high signal when the cowboy is on the screen. Are similar readings expected when running the test rom? Start to finish or only during the shifter test?

My scope does show virtually the same picture as that so it appears that the SAMPLE signal is correct on the daughter board.

This is inverted by F3 before entering the 7442 E3-12. According to the truth table, this will cause all of the port lines to be high

The next thing I noticed on the 7442 @E3 was that while Vcc is 5v, all of the port lines at only at 4vdc. Ports 4 and 6 are not a totally flat line, but the variation is only about 0.1v

What I really don't understand is the inconsistency…. 2 different programs running will sometimes reset very soon after booting and other times get into the attract screen or shifter test before resetting. If it is a stuck pin or bad trace or solder bridge, wouldn't we see the same behavior each time?

Is this more indicative of a bad cap or diode? Sense seems to be working, the watchdog is barking, so the counters are not getting cleared consistently, right? So what tells the watchdog timer to reset? Port 4 off E3 needs to go low to reset the 74161s at D2-1 and E2-1.

I guess I need to know exactly what the 4 inputs to the E3 are doing so that I can confirm what should be happening on the port lines.

Thanks for you patience!

 

[N24005]

I am back to just having a sound issue !!(which is where this all started)

The source of my reset and shifter issues was the jumper wire on the power board was only holding on my a strand. As a result the reset line was totally inconsistent

Thanks for listening