VOGONS


First post, by fredericsoares@sapo.

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Good evening, I'm back from repairing a SEAGATE: ST157A disk and I would like to know if anyone has the same disk and can tell me which smd burned out. I burned an SMD that is in front of the capacitor (positive side) 475 25v. I'm grateful

Reply 1 of 8, by dominusprog

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Can you be more specific?

Duke_2600.png
A-Trend ATC-1020 V1.1 ❇ Cyrix 6x86 150+ @ 120MHz ❇ 32MiB EDO RAM (8MiBx4) ❇ A-Trend S3 Trio64V2 2MiB
Aztech Pro16 II-3D PnP ❇ 8.4GiB Quantum Fireball ❇ Win95 OSR2 Plus!

Reply 2 of 8, by Horun

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Yeah more specific, how about a picture ? This does not seem to help as I see no 475 25V cap: https://i.ebayimg.com/images/g/GLsAAOSwhgBltrep/s-l1600.webp

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 3 of 8, by Deunan

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The only caps big enough to have both value and voltage rating printed on them are the tantalums, and there is one 4u7 25V on the PCB. Black, next to crystal resonator and the power connector nearby. Assuming it's this one, which particular SMD in the area burned? If anything I would assume it's the tantalum cap itselt that shorted and caught fire.

As best as I can see the stuff next to crystal is 0 ohm shunt and a ceramic cap, probably about 20-30 pF. The black box over the tantalum cap might just be a small SMD filter choke. Or something like 100nF 25V ceramic cap. Easiest way to tell would be to check if the tantalum in question is connected to input power with it missing, if not it has to be a choke.

Reply 5 of 8, by Deunan

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fredericsoares@sapo. wrote on 2024-05-28, 11:28:

I think the capacitor is shorted and caused the SMD in front of it to burst

Most likely a choke then but do make sure, if putting a piece of wire across the pads doesn't short the power connector then it's pretty safe to test the HDD with this "fix". After you replace the cap the blew up of course, and clean the PCB.

Reply 7 of 8, by Deunan

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No, I meant replacing the burned out element in red circle with a wire, since it was most likely a choke and you won't be able to guess now what particular value it had (probably a few uH). Well I suppose you could try to use thinner wire that would be like a fuse but that is a lottery. Too thick and it won't blow, too thin and it might blow even during normal operation. So I don't think there is much point in doing that. Better to use a known good AT PSU that will trip on short. Some people use 550W+ ATX PSUs and these things can pump out a lot of current on 12V line before shutting down, this is not good for older equipment that can have random shorts on 12V line due to capacitors.

Again, make sure it was a choke, a not another capacitor. For example measure the resistance on 12V input on power connector after you put the wire in. If it looks like short now (below 12 ohms) then obviously it was not a choke after all.