Replacement for a DEC 7474 Chip

[Eric Smith]

Those should be fine. Only the more complex parts had issues, not the
simple gates.

On Sun, May 15, 2022, 02:04 Rob Jarratt via cctalk <cctalk at classiccmp.org>
wrote:

> Oh dear, while I was ordering an original 7474 I ordered some other parts
> that were connected to the same bad chip in case other chips are damaged,
> and I ordered a Fairchild 74LS08! I will ask them to change it for a
> Motorola part they also have.
>
> > -----Original Message-----
> > From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of dwight via
> cctalk
> > Sent: 14 May 2022 23:36
> > To: Paul Koning via cctalk <cctalk at classiccmp.org>
> > Subject: Re: Replacement for a DEC 7474 Chip
> >
> > What ever you do, don't use a Fairchild part. When I worked for Intel in
> the
> > 80's, we finally band using Fairchild for any latching device. They
> failed
> on
> > pullup current, even when the parts were sent back and they claimed they
> > were good. We just gave up on them, we couldn't hold production while
> > they figured it out.
> > We had a similar problem with PowerOne, a manufacture of power supplies.
> > Since it was a custom supply, we had to send someone to their plant to
> fix
> > their final test.
> > Dwight
> >
> >
> > ________________________________
> > From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Nigel Johnson
> > Ham via cctalk <cctalk at classiccmp.org>
> > Sent: Saturday, May 14, 2022 10:50 AM
> > To: Paul Koning via cctalk <cctalk at classiccmp.org>
> > Subject: Re: Replacement for a DEC 7474 Chip
> >
> > AFAIR LS can only drive one unit TTL load.
> >
> > I may have some 7474, even of that vintage, if you cannot find any
> anywhere
> > else.
> >
> > cheers,
> >
> > Nigel
> >
> >
> > Nigel Johnson, MSc., MIEEE, MCSE VE3ID/G4AJQ/VA3MCU Amateur Radio,
> > the origin of the open-source concept!
> > Skype:  TILBURY2591
> >
> >
> > On 2022-05-14 13:48, Paul Koning via cctalk wrote:
> > >
> > >> On May 14, 2022, at 1:41 PM, John Robertson via
> > cctalk<cctalk at classiccmp.org>  wrote:
> > >>
> > >> On 2022/05/14 10:11 a.m., Rob Jarratt via cctalk wrote:
> > >>> Hello,
> > >>>
> > >>> I have found a bad DEC 7474 chip on my M7133 board. Clearly it is a
> > >>> 74<something>74 D flip flop. The problem is I don't know which
> > >>> modern series would be the best one to replace it with. I am sure I
> > >>> have seen a list somewhere of modern equivalents for some DEC chip
> > >>> numbers, but I can't remember where.
> > >>>
> > >>> If it helps at all, on the PDP 11/24 printset it is E78 on page K6
> > >>> of the schematic (p157 of the PDF).
> > >>>
> > >>> Picture of the failed chip here:
> > >>> https://rjarratt.files.wordpress.com/2022/05/damaged-dec-7474-4_li.j
> > >>> pg
> > >>>
> > >>> Can anyone tell me what the best modern equivalent is likely to be?
> > >>>
> > >>> Thanks
> > >>>
> > >>> Rob
> > >>>
> > >> You are stuck with using an original 7474 family assuming this is
> driving
> > other early TTL. 74LS74, and others simply don't have the drive
> capability
> to
> > work.
> > > I know LS has less fanout, but is it not able to drive plain 74xx at
> all?  That
> > doesn't sound right.  If the circuit in question runs near the fanout
> spec
> of
> > plain 74 the yes, 74LS won't work.
> > >
> > > Spec sheets and the actual schematic will give a definitive answer.
> > >
> > >        paul
> > >
> > >
>
>