MC678P chips needed.

If any one has a tube of MC678P's they would like to part with, the company would be most willing to buy them..

We need them to keep an original, first one every made, irradiation unit operating to its closes original state.

Recently I was informed that they have been having some issues with arcing in the vessel or some where, and they have almost depleted the stock of replacement hex inverter chips. This is on a board that is part of the interlock and voltage monitor and drives reed relays, which in turn, drives larger relays.

Looking around I find the chinese market are more than willing to sell us some. But our finance department really does not want to go this route if possible, we would rather buy from a US supplier or just some left over stock some one wants to unload.

In any case, we rather not use NTE.. We want MC678P marked parts.

I've already got a daughter board in the works, that will use some bipolars and will plug directly into the 16 pin dip socket, if it comes down to that.

Thanks.

Jamie

Reply to
Jamie
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Try reposting to s.e.repair and s.e.components.

?-)

Reply to
josephkk

There are folks out there who can mark whatever numbers might match your request on "probably close enough" parts, just to give you that feeling of confidence.

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
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Reply to
Spehro Pefhany

We found some in the US, 16.50 each.. we have 25 coming...

Thanks.. P.S. Most of the repair guys seem to think EGC, NTE or what ever is close enough. We don't deal that way, we want original numbers to insure we have the correct part.

Plus we needed a tube of them, not just a couple which is why I thought maybe some old timers here had some in their bins, I know I have a collection of hard to fine chips. ;)

Jamie

Reply to
Jamie

Yes that is true however, I spent hours looking at old logic of various families and I could not find one that matches this one, this is an odd ball part.

So basically it is a 6 unit hex inverter with 4 units using a single enable and the other two using a single enable line, simply by combining the gate inputs of (NAND gates), into one.

On top of that, it operates on 15 volts and drives reed relays directly from the outputs and has open collector outputs.

Putting all that in perspective, I don't think there are too many different devices in a 16 DIP P package that would replace this.

Unless there are some gate arrays that can be programmed to do so :)

We'll see tomorrow when the tube arrives!

Jamie

Reply to
Jamie

ECG ceased to eixist over 12 yewars ago: "In January 2001 NTE acquired the assets of the ECG division of Philips N.A."

So, you buy something with the right markings? I can buy thousands of empty, dummy ICs with no markings and put anything on them.

ECG & NTE are the original parts, just 'house numbered' Of course you'll never understand what that means. It doesn't matter, since whatever replacement NTE had, its marked Obsolete-NLA.

Reply to
Michael A. Terrell

That crap has been obsolete for decades.

Reply to
Michael A. Terrell

Aren't P-Dips obsolete?

15V? PLD? You gotta be kidding.

Though some is still used. I rather like the SC-70 1G parts. I'm even designing in a 74HCT14 into a board, now. I need 5V drive from a

3.3V CPLD (dumb regulator needs 5V on its clock input).
Reply to
krw

I probably have some in my parts bins... I worked for Motorola SPD from 1962-1970, but I would _never_ provide any to such a snot as Jamie >:-} ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

I find hanging a open collector output being driven from what ever logic family you want to use works nicely. The devices on the outside can use their own pull up if needed, at various voltage. Of course, you need to NOT (!) the logic for that.

Jamie

Reply to
Jamie

Well, 15V would be a stretch for 3.3V programmable logic parts, for instance. (Queue Joerg for sound effects.)

A tangential point regarding 3.3V MCUs with 5V-tolerant inputs. It seems that the usual approach to making a 5V output signal is to use OC mode with pull-ups to 5V, leave the corresponding register bits at zero, and toggle the data direction bits to toggle the output.

Is there some general wisdom about doing this versus just using the OC mode normally? Something about the protection network, maybe?

Cheers

Phil Hobbs

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Principal Consultant 
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Reply to
Phil Hobbs

That's ok Jim, you can keep your chips. I don't want to become one of your elusive pals.

I rather spend the money and not kiss your feet.

Jamie

Reply to
Jamie

ISTR some chips have caveats on how different the output voltage can be relative to Vdd. IOW, it's okay if you derive the 3.3 from the 5V but if the 5V pullup is applied with Vdd too low the chip might not be happy.

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
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Reply to
Spehro Pefhany

Not sure about what you're asking her but, If you were to employ a OC output into a design, one needs to invert the logic at the MPU.

Of course the idea is to not have to worry about external voltages making their way to the low voltage bus using OC. Also it serves to allow you to pull down other devices that can be energized via low side.

We use encoders with open collectors. Some times they are PNP (source) or (NPN) sink. The sink (OC NPN) can connect to any digital device of various voltages, normally up to the 24 volt level when the encoder can only handle 3.3 or 5 internally. If the receiving device requires the input to follow it's logic level voltage state, then a mere pull up will do. if the pull up does not have enough speed, you can then put a PNP on the input of that receiving device.

AS for PNP open collector, they are not so popular, mostly used where input devices require source signals. In that case, you need to make sure the encoder or prox etc is operating at the same level of supply.

Devices that can trigger on sinking the input are more desirable.

Some times we use darlington components because of the high beta and they match 3.3 logic very closely for base drive, they also have a diode in the body that helps for reverse voltages. Then we put a low voltage zener at the base to common. This removes the unwanted transient from the miller effect and you don't need high levels of voltage entering the bus.

Jamie

Reply to
Jamie

As long as you don't care about symmetry or rise time, it works.

Reply to
krw

Iff it's an inverting gate. The same applies to a totem pole driver.

But it gives a crappy rise time, if that's important. Unfortunately, in my case the rising edge is the important one.

I use PNPs all the time. The sex if the driver is determined by the more important quiescent state. If the low state current is important, for example, the signal is low under battery power, a PNP makes a lot of sense. PFETs work, too, but they're about 10X the cost.

As you note, sometimes you need to source current, too.

I suppose. NPNs save a half cent.

Darlingtons cut way into the noise margin in the low state, though. Ick! If I needed to save that much current, I'd use a FET.

Reply to
krw

He would put them in backwards, anyway. Want to bet the stuff he found are fakes, or rejects? Didn't that family go obsolete before RTL?

Reply to
Michael A. Terrell

Is the particular application even using those strobe inputs? If not, there are a bunch of inverters in that family to choose from. Also, regardless, there is the same layout in another family member that has resistor outputs , that's a 15K pull-up which should also work in the same circuit, an extra milliamp isn't going to break the bank. And then everything in that family except of a few parts with active pull-up, can be wire-OR-ed if that's wha t they're doing.

Reply to
bloggs.fredbloggs.fred

are a bunch of inverters in that family to choose from. Also, regardless, there is the same layout in another family member that has resistor outputs, that's a

15K pull-up which should also work in the same circuit, an extra milliamp isn't going to break the bank. And then everything in that family except of a few parts with active pull-up, can be wire-OR-ed if that's what they're doing.

Yes, the enable inputs are being used.

There is a master ready signal that enables the ENABLE line on the pair, one of these pairs then drives the ENABLE line for the other 4.

Mean while, the inputs to these inverters are receiving ready active signals from different points.

There is a sequence of events that must take place in order to insure proper operation before starting the units.

Jamie

Reply to
Jamie

I'm really having trouble understanding how a negative logic AND output can function as a positive logic input enable for the other ANDs.

Reply to
bloggs.fredbloggs.fred

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