Asus P5A Missing Components \ VOGONS

Asus P5A Missing Components

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First post, by wiibur

Posted on 2022-11-30, 05:28

wiibur Offline

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I picked up this Asus P5A Rev. 1.03 a while back and noticed some missing components after I had been using it a bit. It looks like D7 and D8 have been knocked off.

I haven't noticed any instability on the platform running some games and benchmarks. Does anyone know the function of the circuit these components are on or their part #/value so I can replace them?

Reply 1 of 5, by Dorunkāku

Posted on 2022-11-30, 06:44

Dorunkāku Offline

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It looks like 1N4148 SMD Glass Diodes.

Reply 2 of 5, by rasz_pl

Posted on 2022-11-30, 10:26

rasz_pl Offline

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1.05 doesnt have those diodes so its nothing that important 😜
I do have boardview for P5A-B (AT version)
now comparing P5A-B and P5A revisions those three 74 series chips get integrated into one proprietary Asus "AS61256-8"
4 diodes on ATX version are close to those chips, but on AT version they are most likely D1-4 close to ALI chip on the other side https://theretroweb.com/motherboards/s/asus-p5a-b
They are wired directly to RS232 header Ring Indicator (RI) signals, 2 diodes clamp the signal between ground and 3.3V, two others combine it into one common RI . I guess without those two diodes you wont be able to ... host a BBS? 😀

https://github.com/raszpl/FIC-486-GAC-2-Cache-Module for AT&T Globalyst
https://github.com/raszpl/386RC-16 memory board
https://github.com/raszpl/440BX Reference Design adapted to Kicad
https://github.com/raszpl/Zenith_ZBIOS MFM-300 Monitor

Reply 3 of 5, by wiibur

Posted on 2022-11-30, 10:53

wiibur Offline

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Thank you for the detailed info. Sounds like it won't be much of an issue since I don't intend on using the RS232 ports.

Reply 4 of 5, by rasz_pl

Posted on 2022-11-30, 11:22

rasz_pl Offline

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Its not even normal rs232 usage. Its specifically a signal used by modem to signal ringing.

Reply 5 of 5, by wiibur

Posted on 2022-11-30, 11:23

wiibur Offline

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Hah, even more specific of a use case. Understood.

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