Is this components compatable?????

[roadrash]

I am repairing a old IBM PC 5170 (AT) & i am having keyboard problems which could be the fault of a SN74ALS00N but I cant find many online in the UK. I have however seen SN74HC00N-74HC00N-IC-QUAD-2-INPUT-NAND-GATE
are these direct compatable replacements as I have found 10 of them available.

many thanks

[jiroy]

Re: Is this components compatable?????

They are basically the same , the only difference is in the type package , here is a Texas Instruments PDF to help :

https://cdn.badcaps-static.com/pdfs/...258dd21a5c.pdf

[stj]

Re: Is this components compatable?????

NO, they are very different.

the output swing, drive current and speed are not compatable.

[stj]

Re: Is this components compatable?????

btw, did you test it?
what test gear do you have?

[Curious.George]

Re: Is this components compatable?????

I am repairing a old IBM PC 5170 (AT) & i am having keyboard problems which could be the fault of a SN74ALS00N but I cant find many online in the UK. I have however seen SN74HC00N-74HC00N-IC-QUAD-2-INPUT-NAND-GATE
are these direct compatable replacements as I have found 10 of them available.

That depends on how it is used in the circuit -- what drives it and what it drives. Chances are, they were using ALS devices elsewhere on the board and didn't want to bother with using a different logic family here.

Functionally, they are all identical. They are all "quad 2-input NAND gates" and share the same pinouts.

But, they are implemented using different "process technologies" (like caps can be implemented with different chemistries and construction techniques).

The ALS devices tend to be faster than the comparable HC devices. And, tend to be less affected by load capacitance (i.e., whatever is hanging on the output).

HC devices use less power and the power they use is directly proportional to the speed at which they are switching (ALS devices essentially use more power to start with and only significantly increase at the upper end of their frequency limits). An HC device that isn't switching essentially uses "no" power.

HC devices present higher input impedances so have less loading on the signals that drive them.

ALS devices have poor "current sourcing" capabilities (output "HIGH"). HC devices have identical output source and sink capabilities (e.g., if you are driving an LED with an ALS device, you would want to connect it to the cathode of the LED and illuminate the LED by driving the output of the ALS device LOW; for an HC device, you could connect to the anode/cathode and drive the output HIGH/LOW, your choice)

The HC parts have a threshold voltage of ~2.5V that is largely invariant over temperature (though it is NOT invariant over Vcc changes!). ALS devices have a much lower threshold that moves with temperature (though not with Vcc).

How much of this REALLY is important in your selection? <shrug> depends entirely on how the component is being used. You can test the device relatively easily (assuming the output tends to be LOW) by injecting a LOW on each input and observing for a (brief!) LOW-to-HIGH transition on the associated output.

[A logic probe and pulser are excellent for this as the pulser will override the current input level momentarily -- which, of course, may affect something else that the signal is wired to! ]

Presumably, you've swapped keyboards and the problem stays with the PC. Some vintage machines had a small fuse in the power lead to the keyboard (typ. a "picofuse"). If the keyboard doesn't light up at all and is otherwise unresponsive, verify that you have power AT the keyboard connector.

[jiroy]

Re: Is this components compatable?????

Yes they are identical except for packaging , i'm tired telling stj; to read the whole things always

[stj]

Re: Is this components compatable?????

bullshit.

they arent even official equiv's
that would be the AHCT series.
get yourself the fucking Ti Logic family databook - it's a free download.

[Curious.George]

Re: Is this components compatable?????

Yes they are identical except for packaging , i'm tired telling stj; to read the whole things always

No, they are NOT identical. They are functionally identical but differ greatly in the specifics of their implementations.

There are reasons that we have logic functions offered in 4000 series CMOS, "legacy tonka toy logic", 'S, 'LS, 'ALS, 'AS, 'AUC, 'LVT, 'LVC, 'F, 'HC, 'HCT, MECL II, MECL III, 10K ECL, 100K ECL, HiNiL, all the 54xx variants, 93xx, etc.

Pinouts may be the same (or not) and the logic equations for the functions implemented may be the same -- but, the specifics of the actual device's implementation can vary in ways that can make "identical" parts completely incompatible in a particular circuit.

A basic overview of the characteristics of the different technologies:
https://www.fairchildsemi.com/collat...tion-Guide.pdf

As the OP hasn't told us what his circuit is, there's no way to know if one is a "drop-in" replacement for the other. Just saying you're having a problem with the keyboard doesn't tell me how this component might possibly be related to the circuit you're troubleshooting in enough detail to be able to say "Yeah, that will likely work" or, "Nope."

(with my recollection of the old AT's design, I can't recall any place where it is LIKELY to cause a problem; but, given that it takes time and effort (and risk!) to replace a component (possibly TWICE), I'd want better assurances...)

[jiroy]

Re: Is this components compatable?????

We are talking here about the SN74HC00N specifically , and not some other variants ..
Reread the Texas Instruments PDF ..

[stj]

Re: Is this components compatable?????

i'll make this real simple for you,

HC is compatable with 40 series,
HCT is compatable with 74LS series - the T = TTL compatable.
HCT is not fast enough to match an ALS device.
AHCT is compatable with ALS.

you think they make all these fucking versions for fun???

[roadrash]

Re: Is this components compatable?????

Thank you everyone Didn't mean to start a argument. Samms Computerfacts recommended replacing two certain chips and this in this PC and this is one of them, but It must be 100% compatible. So thanks

Ive seen these which are SN74LS00N are these ones OK to use?

https://www.ebay.com/itm/10pcs-SN74L...MAAOSw5bFZX1fe

[jiroy]

Re: Is this components compatable?????

i'll make this real simple for you,

HC is compatable with 40 series,
HCT is compatable with 74LS series - the T = TTL compatable.
HCT is not fast enough to match an ALS device.
AHCT is compatable with ALS.

you think they make all these fucking versions for fun???

stj; you're absolutely in another valley , I was talking about SN74HC00N varieties , like SN74HC00PW or SN74HC00NS or SN74HC00DB as compatible with different packages ..
Why ? , simply because SN74ALS00N is discontinued and most important , it's a Nand gate while SN74HC00N is available and AND Gate , get it ? ...

[Curious.George]

Re: Is this components compatable?????

stj; you're absolutely in another valley , I was talking about SN74HC00N varieties , like SN74HC00PW or SN74HC00NS or SN74HC00DB as compatible with different packages ..
Why ? , simply because SN74ALS00N is discontinued and most important , it's a Nand gate while SN74HC00N is available and AND Gate , get it ? ...

Have you read the OP's question completely:

...could be the fault of a SN74ALS00N but I cant find many online in the UK. I have however seen SN74HC00N-74HC00N-IC-QUAD-2-INPUT-NAND-GATE are these direct compatable replacements

My understanding of English grammar sees that as:

• he's got an ALS00 in his misbehaving circuit (happens to be in a plastic DIP package -- N suffix)
• he suspects it to be the cause of his problem(s)
• he can't find any replacement ALS00's (no idea if he's looked for CERDIPs)
• he has, however, found some HC00's (also in plastic DIP package!)
• and would like to know if he can replace the dubious ALS00 with an HC00

He makes no mention of other package types in the devices he references.

If your intent was to tell him "see if you can find a 74ALS00 in another package type that is mechanically compatible" then your wording leaves much to be desired... (i.e., something as simple as "see if you can find a CERDIP ALS00" woul dhave been more to the point)

[jiroy]

Re: Is this components compatable?????

Sorry curious.georges .. I'm done with this thread , for lot of reasons

[Curious.George]

Re: Is this components compatable?????

Thank you everyone Didn't mean to start a argument. Samms Computerfacts recommended replacing two certain chips and this in this PC and this is one of them, but It must be 100% compatible.

Chances are, it only needs to be compatible in some portion of its characteristics/capabilities. You design a circuit with certain criteria in mind and pick from a variety of components that can fit those criteria. Other "nonessential" criteria can be allowed to vary. (Engineering is the art of figuring out the "Right Compromise").

The problem you're facing (and that most folks making repairs without complete documentation of the circuit they're troubleshooting) is that you don't know what criteria were important to the engineer in the selection of that particular component for that particular spot in the circuit.

Did he need the speed that the ALS device afforded? And, didn't want to waste the power that an S device would require? Did it really need to be a NAND gate instead of an AND followed by an inverter? Or, an OR preceded by inverters?? Were the signals that fed it not guaranteed to provide more than a Voh of 2.4V (in which case, you have to select a device that you KNOW will recognize 2.4V as a HIGH cuz it may never see an input at any higher potential than that!). Or, did the engineer just have a preference for ALS components and use them throughout the design (to cut down on the number of DIFFERENT components in the bill of materials)?

Do you have a reference (URL or attachment) for the document that is telling you this might be the problem?

Ive seen these which are SN74LS00N are these ones OK to use?

LS is yet another beast. So, you're asking a new version of the same original question -- with the same replies! ("it depends")

All of these "logic families" have different characteristics. Manufacturers spent a fair bit of time designing them, manufacturing them and stocking them... FOR A REASON.

Why do you drive a (e.g.) Ford and not a Chevy? Or beemer? All of them have four wheels, a steering wheel, engine, accelerator, brakes and other required safety equipment. Did you have a loyalty to a particular brand that biased your decision? Maybe a specific budget? Or, perceived "quality" differences in the product offerings? Or, maybe you were set on a particular shade of green that was only offered by one of the manufacturers...

If I see you driving that vehicle, I have no way of knowing what criteria you used to make your selection. If you tell me (car dealer) that you want to replace it, I'll go looking for the same EXACT car (make, model, year, etc.) -- unless you tell me what aspects of THAT choice were not important in the original decision ("As long as it is this shade of green, I don't care about anything else" vs. "It has to be a V8 but I don't care about the color or manufacturer" vs. "My mechanic only works on beemers...")

What specifically are you seeing as a problem? Is the keyboard completely dead? Do the indicators n the keyboard work -- but not the keys? Do certain keys work but not others? Etc.

With the little you've said, so far, all I can safely (meaning effort that you won't later have to undo/redo/repair) suggest is (powering off as appropriate):

• test the chip "in circuit" (logic probe and pulser being the most expeditious)
• remove the chip if it appears to be bad
• verify the output signals of the chipless circuit aren't being forced to particular levels (if there is no chip in place, they should "float")
• install a 14 pin socket (so you can change your mind about the actual replacement component that you choose to install, there)
• plug the HC (or LS or S or ...) device into the socket
• see if your symptoms change (note that I've not said "see if it works" because it MAY work, or not, and may not be predictable given that we don't know what the component might experience two hours from now in terms of signals)

If the symptoms change, then there MAY be some involvement of that component. If they change but are still not quite right (and you don't suspect any other problems in the machine that could explain it), then it could be that some aspect of this component isn't quite what it needs to be; tha ALS may have been chosen for a very specific characteristic that the HC, LS, S, etc. can't address.

I'll wager it either "works" or you're looking at the wrong component as the cause of the problem.

[Curious.George]

Re: Is this components compatable?????

stj; you're absolutely in another valley , I was talking about SN74HC00N varieties , like SN74HC00PW or SN74HC00NS or SN74HC00DB as compatible with different packages ..
Why ? , simply because SN74ALS00N is discontinued and most important , it's a Nand gate while SN74HC00N is available and AND Gate , get it ? ...

I suspect a good many components in the kit we repair fall into the "discontinued" or "no longer available" category. As a result, some things are simply not repairable -- without looking for NOS or "pulls".

Might not help someone in the UK, but:

https://www.jameco.com/z/74ALS00--Ma...14_245294.html

(319 "in stock" at a whopping 39c/each)

The OP appears to be new to this. The LAST thing I want to see is him (?) get discouraged by investing the effort to make a diagnosis and repair -- only to discover that "it didn't work". Success is an important "future motivator".

OTOH, it is important for him to understand why there are so many choices in components; why every PC (TV, radio, etc.) isn't an exact clone of every other one! Why a 105C cap can be "added value" in this spot in this circuit but a complete waste of money (85C being adequate0 in some other portion of the circuit. Precision is important in the answers he's given.

[I can describe a complex software algorithm in a few sentences that any of my peers would be able to implement correctly -- because they would implicitly know all of the details that I'd not ennumerated. A newbie, OTOH, would spend ages discovering those issues by trial and error ("Why do I have to test if the divisor is 0?")]

and most important, it's a Nand gate while SN74HC00N is available and AND Gate , get it ?

Um, a 74x00 is always a NAND gate (functionally, HC00, ALS00, S00, F00, HCT00, etc. are all identical -- their logic equations are the same: quad 2-input NAND)

[stj]

Re: Is this components compatable?????

yes, unlike jiroy i deal with this all the time, i repair 80's digital electronics.

[Curious.George]

Re: Is this components compatable?????

yes, unlike jiroy i deal with this all the time, i repair 80's digital electronics.

And that's where the "art" comes into "repair" -- when there is no "exact replacement" for the failed component.

This is why many "board swappers" are sorely limited in their abilities to affect repairs: they RELY on having an exact replacement available (for the board). It's a whole different matter when you're trying to repair/replace components IN a circuit.

I have some "real time clock/NVRAM" chips that have died in my Sun workstations. I can purchase an overpriced, discontinued component and hope that its INTERNAL battery hasn't degraded in the years its been sitting on a shelf, waiting for a buyer. Or, I can surgically isolate the defective internal battery from my existing chips and piggyback fresh cells on top of the packages (e.g., CR2032's).

Installing a battery holder atop the defective chip means my efforts will serve me when in the future, when THESE cells are exhausted!

[eccerr0r]

Re: Is this components compatable?????

Dammit. I had a motherboard with a *soldered* RTC+NVRAM chip whose battery died. First pass I had a lobotomy done on the chip in situ, found the battery, and soldered an external battery. However I found that it leaked so much current that the new coin cell would die in a few weeks... *sigh* Not sure why it leaks so much power.

Ended up desoldering the chip, adding a socket, and looking for a replacement, else powering it with 5VSB...

[Curious.George]

Re: Is this components compatable?????

Dammit. I had a motherboard with a *soldered* RTC+NVRAM chip whose battery died. First pass I had a lobotomy done on the chip in situ, found the battery, and soldered an external battery. However I found that it leaked so much current that the new coin cell would die in a few weeks... *sigh* Not sure why it leaks so much power.

Ended up desoldering the chip, adding a socket, and looking for a replacement, else powering it with 5VSB...

Are you sure you isolated the defective battery from the new battery, in the process?

Old (1980's vintage) machines used RTC's with really heavy quiescent power requirements -- the "CMOS battery" would be the size of a few AA cells ("Made in Israel" -- Tadiran). But, newer CMOS processes are far more power efficient. In some cases, replacing the battery can be done without losing data!

This guy was a bit "extreme" in the way he exposed the contacts (I just use a Dremel in EXACTLY the right place)

https://gigawa.lt/gigawa.lt/Sun_NVRAM.html

The last photo is more in line with where I'll end up (I'm delaying the task as I also want to update the FC-AL drives to 300GB while I have the covers off; probably a whole day to do two machines!).