Space Invaders Multigame "Bit: Failed"

jeff412

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I just put the Brazington Space Invaders multigame in my SI. During the self test it says Bit: Failed 00 80 80.

Any ideas what this means? The games play but the graphics are a little messed up. Not sure what it is telling me to fix. And I can't find anything online that describes it.

Thanks,
Jeff
 
i'm interested in the fix as i will shortly fit one to a midway L shaped boardset.

do you have the taito boardset or the midway L shaped boardset ?
 
I have the Midway boardset. I did email Scott his response it below.

The SI game has a circuit on it for assisting in bit shift operations.
It gets used by several games like SI and SID. The powerup selftest
runs an extensive diagnostic on this circuit and the diagnostic has
found that it fails in some bit patterns. I think I run like 4096
patterns through it or something like that.

There are several different variations of that circuit depending
on the board types, but the common one that fails is the one
that uses a daughter card on the sound card. If that daughter
card is not making good contact it sometimes gets reported as
a BIT FAIL by the diagnostic. If you have the type of board
that has this daughter card, then I suggesting reseating it
and/or cleaning its contacts. I think there is also a version
that the entire daughtercard is implemented in a custom IC.
There is another version where the daughter card chips are layed
out directly on the soundboard. They all perform the same
function, but done differently. The diag exercises this function.

It is possible because the diagnostic runs an extensive test
on this circuit that the circuit may "appear" to work fine during
gameplay. Or you might notice an occasional pixel from an
invader that does not get shifted correctly as the invaders work
their way down the screen. I would try reseating the shifter
board or chip. But the error is not fatal and you can still
play the multigame even with the failure, but be aware it could
mean some of the gameplay on some of the games will not always
work correctly.

-Scott
 
My problem is that I'm not getting minor glitches in the graphics. On SI I have horizontal lines across the entire width of the screen. I have reseated the daughterboard, but I am going to try again and see if anything changes.

Jeff
 
I cleaned the edge connector and reseated the daughterboard, but I still get the same thing. Sorry about the poor picture quality, but maybe there's enough there to give you the idea of the problem. I haven't figured out the vertical hold on the monitor yet, so it is rolling. That's the reason for the ghosting. The images are clear, just with horizontal lines.

Jeff
 

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Reading through Scott's email a little closer, he suggests reseating the shifter board or chip. Does anyone know what that is on a Midway L-shaped boardset? I thought he was referring to the daughter board that comes off of the cpu board, but maybe not.

Jeff
 
Reading through Scott's email a little closer, he suggests reseating the shifter board or chip. Does anyone know what that is on a Midway L-shaped boardset? I thought he was referring to the daughter board that comes off of the cpu board, but maybe not.

Jeff

On Space Invaders....the shifters are the four 25S10 chips on the daughter board. Midway issue a service bulletin stating a supply problkem with the 25S10's and replaced them with eight 74151 chips. I assume this was a satalite board that plugged into the existing locations of the four 25S10's. I think this is what Scott is talking about.

If you have a Space Invaders Deluxe daughter board....it's an entire different set of chips.

Edward
 
Ok. I have the SI boardset and not the SI deluxe. I do not have the daughterboard that you are referring to. I guess I must have the 25S10 chips in mine.

Jeff
 
Thanks. I'll check that out when I get home from work. I assume these are soldered chips and not socketed?

Jeff
 
Usually, yes....check for bad solder.....or just try re-flowing it...see what happens.

Edward
 
Is it still possible to get the 25S10's anywhere?


EDIT: Never mind, found them at arcadechips.

Jeff
 
Is there any way to test the 25S10's ? They are $5.00 apiece and I hate to just shotgun it without at least an educated guess that they might be the problem.

Jeff
 
Jeff testing as follows:
0. grab the data sheet. Look for the Signetics 74s350 at www.DatasheetCatalog.com - its easier to find as it is a compatible chip and it has more info including truth table and timing diagrams.

1. With a multimeter, test the DC power supply at the chip.
- pin 16 +5v, pin 8 ground. Look for 4.75v to 5.25 volts at pin 16. closer to 4.75v could be problematic. 5.1v is nice. Therefore if below or very close to 4.745v, check you power supply output.

2. with a logic probe:
- check the /OE pin, pin 13. looks like active low so it should be pulsing LOW when enabled by the program code.
If /OE is HIGH then the output pins Y0-Y3(pins 11,12,14,15) go HiZ (high impedance) so the state will be indeterminate as far as the logic probe unless there are PULLUP or PULLDOWN resistors on the same trace for circuits that follow these pins. In which case they will be pulled high or low and wont [necessarily] be pulsing [at that instant in time but should at some time!]
- check the SELECT pins S0 and S1 (pins 10 and 9) - providing your /OE is working, then they should also be pulsing HIGH. As there are multiple possible addresses, the lines may remain low, or puls low, or either one or both may pulse HIGH. You'll need to read the schematics to interpret how they are implemented as discrete shofters or part of a wide bit shifter. In the signetics datas=heet, refer to page 5-502 and 5-503 for example implementations.
Also refer to page 5-498 "descripotion" where it describes the various implementation modes.
mode 3. should mean all outputs will pulse high/low depending on data byte being shifted. Not sure if that is the mode yused or not - some of the si repair gurus can help there.
mode 1. depending on the direction of shift you may see Y0 or Y3 remaining LOW and others pulsing
mode 2. may mean the y3 bit being duplicated down to y2, y1, y0 so look for them equalling or the same as y3 ? again not sure - si repair gurus should be able to help there.
Also have a look at the truth table. Monitor all of pins 1-7 to check what they are doing to help interpret the output according to the truth table.

Thats all I can come up with for you. Hope that is some help.
 
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