SN74LS257N replacements?

texasmame

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Poking around online for chips for the trackball input for Centipede as it's hosed.

SN74LS257N is the actual part number on the chip. I've also found SN74LS257BN and SN74LS257B and NTE74HC257 (NTE equiv. for LS257) online.

Should any one of these work in place of the original NTE74HC257N? I'm trying to interpret the data sheets but not sure that the differences I see will make a difference but they all do appear to be a Quad 2 input multiplexer with 3 output states.

TIA!
 
Any 74ls257 will work fine, the suffixes are vendor specific and usually only denote whether they are military or medical grade. The prefixes are vendor specific, SN is Texas Instruments, MB is Fujitsu etc etc. None of it matters for arcade gear.
 
Super, thank you, guys.

Looks like the LS257 part is the important bit as far as games goes and presuming the HC prefix is fine as that's the NTE equiv. for LS257.

Thx!
 
Yes, LS257's, and similar, are not uncommon in input circuits.

And yes, the "LS257" portion of the part number is the most important. The "74" is typically implied, and other prefixes and suffixes are generally unimportant. Any manufacturer will do.

NTE parts, in general, are a last resort. They are often NTE's own proprietary numbering system, and they are almost always much more expensive than "regular" parts. I only resort to NTE when originals are no longer readily available.

And if "LS" type is not available, "HCT" is a better substitute than just "HC". It has TTL-level interface (i.e. it has compatibility with "LS" series chips). I typically by LS chips for general use. Only occationally should you run into an application where you must match the exact type as the original.
 
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Yes, LS257's, and similar, are not uncommon in input circuits.

And yes, the "LS257" part is the most important. the "74" is typically implied, and prefixes and suffixes are generally unimportant. Any manufacturer will do.

NTE parts, in general, are a last resort. They are often NTE's own proprietary numbering system, and they are almost always much more expensive than "regular" parts. I only resort to NTE when originals are no longer readily available.

And if "LS" type is not available, "HCT" is a better substitute than just "HC". It has TTL-level interface (i.e. it has compatibility with "LS" series chips). I typically by LS chips for general use. Only occationally should you run into an application where you must match the exact type as the original.

More good info, thx.

Yeah, the NTCs are pretty pricey but I'm willing to spend a bit more to get them NOW as they are at Fry's which, luckily, is a 15 minute drive.

I love that place. :)
 
I keep those in stock too... and am in the metroplex. Much cheaper than Fry's...

Or you can go to Tanner Electronics for parts too.

Don't replace a 74/F/HCT/L/LS/S with a C or HC... C and HC are CMOS logic levels which aren't always compatible with your TTL/LS logic levels. HCT is a CMOS chip with TTL compatible logic levels.

You can usually get away with replacing a chip with one from a different family (L=Low Power, LS = Low Power Schottky, S = Schottky, F = Fast, HCT = High Speed CMOS TTL Compatible) but not always. It depends on the timing of the circuit.

RJ
 
I keep those in stock too... and am in the metroplex. Much cheaper than Fry's...

Or you can go to Tanner Electronics for parts too.

Don't replace a 74/F/HCT/L/LS/S with a C or HC... C and HC are CMOS logic levels which aren't always compatible with your TTL/LS logic levels. HCT is a CMOS chip with TTL compatible logic levels.

You can usually get away with replacing a chip with one from a different family (L=Low Power, LS = Low Power Schottky, S = Schottky, F = Fast, HCT = High Speed CMOS TTL Compatible) but not always. It depends on the timing of the circuit.

RJ

Well, crap. Looks like another trip to Tanner as they are quite a bit closer than you. Wish those HC NTE ones at fry's would do the trick. :(
 
Since HC cmos logic chips can be triggered by 3.3 volts as a High/on state. This might case you issues in some application where your normal 5 volts are normally required to trigger a High/ON logic state. Since this is design as an input chip, I would look for a 74LS257 Chip instead because the HC chip just because the nature of Cmos IC will not put up intermittent connection problems that seem to plague some of the centipede trackballs.
 
Yes, but that would require some circuit patching and isn't always the option.

Don't patch the circuit, patch the chip. Clip three legs on the dead gate, clip three legs on the good gate, jumper from "good" solder pads to the good gate. Faster than a desolder.
 
Don't patch the circuit, patch the chip. Clip three legs on the dead gate, clip three legs on the good gate, jumper from "good" solder pads to the good gate. Faster than a desolder.

Assuming you mean this is possible for the chip that's currently in there, I'm up for this but have no way of telling which are good pins for what I need. I can tell via the schematic which pins have the tracball inputs, tho.
 
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Assuming you mean this is possible for the chip that's currently in there, I'm up for this but have no way of telling which are good pins for what I need. I can tell via the schematic which pins have the tracball inputs, tho.

Look at the diagram on the spec sheet. You will see 4 identical gates with 2 inputs & 1 output each. Two on one side, two on the other. I don't have it in front of me, but it will be something like this

> 1 - Vcc
> 2 - in 1
> 3 - in 1
> 4 - out 1
> 5 - in 2
> 6 - in 2
> 7 - out 2

> 8 - gnd
> 9 - in 3
> 10 - in 3
> 11 - out 3
> 12 - in 4
> 13 - in 4
> 14 - out 4
 
Assuming you mean this is possible for the chip that's currently in there, I'm up for this but have no way of telling which are good pins for what I need. I can tell via the schematic which pins have the tracball inputs, tho.

There is no unused gate on any of the LS257s in the Centipede input circuitry. You didn't, say, but I guess you're talking about L9 (or maybe D9). In either case, all 4 of the gates are being used. So you may safely ignore the subject advice.

And even in cases where there is a spare gate, I advise replacing the IC. I consider wiring it to another unused gate a bit of a ghetto repair... I spend much of my time working on arcade games properly fixing things which were done "faster" rather than correctly.
 
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Taking into account the last two posts, I guess I'll pass if there are no unused gates. I don't mind a ghetto repair and would do it in this case if it were possible.

Thanks guys! Off to Tanner's! ;)
 
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I guess I'll pass if there are no unused gates.

Unfortunately, if there are no unused gates it won't work.

And even in cases where there is a spare gate, I advise replacing the IC. I consider wiring it to another unused gate a bit of a ghetto repair.

I disagree. You're not hacking up the board or altering it in a way that will be unreliable. Even testing and test points will be valid as documented. If the chip fails later, replacing the chip requires no understanding of how the hack works. Just desoldering the chip will remove the hack and restore the circuit to factory condition. All you're doing is externally rewiring the connection between silicon and pins.

Now if we were talking about borrowing the gate on a different chip, I would agree with you.
 
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