Mac SE miniscribe 20MB hard drive burned component

[jafir]

Is this a resistor? Does anyone have one of these drives that can tell me what the specs are?

 

[Chuck(G)]

Just by its placement in series with a power rail, it's a small inductor--perhaps 10 µH. The value's not terribly critical. However, the fact that it's burned tells me that there's a short to ground on the far side. Check those SMT caps to start with.

 

[smiba]

The top tantalum capacitor is shorted most likely, I've seen enough of them through the times

If you can't figure it out, let me know so I'll dig into my drive to see what it is

 

[NeXT]

The internet implies that this...was...R45. That I can tell from the photo it isn't related to the adjoining power header.

 

[jafir]

So I started measuring stuff, in circuit, and it seemed that the lower capacitor was shorted, like 30 ohms, or at least something on that rail since I didn't remove it. The upper capacitor showed to be in the M ohm range. So I started cleaning the soot off so that I could confirm the values of the the capacitors, and then a check them again. Now the lower one seems to be in the M ohm range, and the upper one shows 150 ohm. I found a photo of a board somewhere on google, and the resistor on that that one seems to be a Dale brand with 1 Ω. It's on the 12V rail and the stuff that still seems shorted on the 5V rail. I guess I need to replace that resistor and pull off capacitors to see if I can find one shorted. I'll start with the ones mentioned above.

I won't lie, I obviously don't have any idea what I'm doing so if I say something stupid, please correct me.

 

[smiba]

If you have a bench power supply you may inject 1 Volt into both rails to see what they actually draw in current. Depending on how shorted the caps are, you can also detect the one that's shorted by putting a dab of alcohol on them. The shorted one will evaporate quicker.

You may increase the voltage if you need a higher current draw to notice the component getting warm, but as you never really know what its shorted with exactly I never really recommend going too crazy. 3.3V would be my max, and that should be way more then enough to detect the failing cap (Also you don't want the drive to actually boot up)

Obviously remove R45 before trying this to rule out the resistor, it has to be removed either way.
Also not entirely convinced it says 1 Ohm instead of "10", although you're probably right.

 

[jafir]

It’s got to be the last one you remove, right? All of the others showed up as capacitors on this magic box. This one seems to be a resistor now.

 

[jafir]

Success! After mouser sending me the wrong size part twice, they finally sent me the right ones and this drive is back to life!

(I’m not complaining, they were super nice and I’m sure they lost silly money filling this order 3 times).

 

[devius]

In the interest of someone finding this thread 10 years from now with the same or similar problem can you explain what you needed to change in the end?

 

[jafir]

I replaced the burned up resistor and also a 22uf 16v capacitor. I actually replaced all of the capacitors, but that was probably overkill, it’s just that I didn’t find the short until I had removed all of them. So I put all new ones back on.