[sdiy] ARP Pro Soloist repair needs SN74148 IC..

[John Speth]

Regarding LS and plain-old-TTL compatibility: I think both are nominally
compatible.  But LS fan-in and fan-out must be carefully considered due to
the higher currents of plain-old-TTL compared to LS TTL.

JJS (old-timer who designed numerous TTL and ECL circuits after graduating
from college)

On Fri, Jun 3, 2016 at 5:40 PM, Michael E Caloroso <
mec.forumreader at gmail.com> wrote:

> The LS series are a direct replacement.  They just consume less power
> and are slightly faster.
>
> MC
>
> On 6/2/16, Jean-Pierre Desrochers <jpdesroc at oricom.ca> wrote:
> > Looking at page 6 of this:
> > http://www.ti.com.cn/cn/lit/ds/symlink/sn74ls147.pdf
> > I have my answer..
> > The LS family has higher input impedance thus for pullup resistors is
> > better here..
> >
> >
> > Le 2016-06-02 09:03, Jean-Pierre Desrochers a écrit :
> >> I am refurbishing a vintage 1976 ARP Pro Soloist and
> >> everything goes well so far.
> >> But when removing all socketed TTL IC's one after each other
> >> to 'clean' their pins before putting them back in their sockets
> >> I noticed one of them had 3 of its pins rusted down very badly and
> >> falling off..
> >> So I have to replace it.
> >>
> >> Looking at the service manual:
> >> http://www.synthfool.com/docs/Arp/ARP_Pro_Soloist-Service_Manual.pdf
> >> pages 54, 55 It's one of the 2 Priority Encoders 10 to 4 Line SN74148
> >> (Z1 & Z2).
> >>
> >> These chips scan many of the presets rocker switches.
> >> My question is can I replace the original SN74148 for 74LS148 ?
> >> The former is very old and almost gone (unless bought at eBay).
> >> So far I found 5 x 74LS148 at a local electronic parts dealer
> >> and I think that they will do but I want to make sure with you guys.
> >> In the past I replaced many SN74xxx for 74LSxxx but these
> >> were in TTL to TTL connections boards.
> >> Here its input impedance issues (switches with pullups) I'm aware of..
> >>
> >> Thanks.
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> > --
> > « L'indépendance, c'est comme un pont :
> > avant, personne n'en veut, après, tout le monde le prend. »
> > Félix Leclerc
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-- 

John Speth, Software Engineer, Avnera
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