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

Jean-Pierre Desrochers jpdesroc at oricom.ca
Thu Jun 2 15:22:07 CEST 2016


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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