Identify the Mystery Components
I’m planning to do a partial capacitor replacement on the power supply of my old Macintosh IIsi computer. After 25+ years, these capacitors aren’t in the best condition, and the PSU doesn’t work correctly anymore. When plugged in, it makes odd clicking sounds for a few seconds, then does nothing, and the computer won’t boot. Occasionally if I plug it in, unplug it, plug it in again, and say some magic words, I can get the computer to boot. But it’s clearly on its last legs, and the research I’ve done says replacing a few key capacitors will likely fix it.
After dismantling the PSU and removing its circuit board, I was surprised by some of the components I found inside. I’ve never looked inside a power supply before, so this was all new to me.
In the center is a relay. I’m not sure why there’s a relay inside a PSU, but there it is. At right is probably a transformer? It has some exposed wire windings, and is located close to where 110V AC comes in, so I assume that’s it. At left is… something. A capacitor? It looks like a rolled up length of plasticized paper, coated in oil.
Here’s a closer look at the mystery capacitor thing.
On the other side of the PSU circuit board are two white plastic towers. They look like they might be removable covers. What are these, and what mysteries do they hide?
At the end of the board opposite the AC power connection, there are two cylindrical components that look sort of like capacitors, but aren’t. They have vertical grooves cut into them at regular intervals around their circumference. The smaller of the two has 4R7 stamped into its plastic case, and the larger one is marked 830. Could these be some kind of high-power resistor, maybe?
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Both of the components marked “sony” seem likely to be transformers to me. The “oil” coated one in particular: look up custom transformer construction some time. The cylinders with slots I don’t have a clue on, though 4r7 sounds more like a cap than resistor. And yes, that’s a lot of inductors: my thought is that it might be an smps with multiple output voltages.
Second Photo, from right to left: Filtering AC power coil set, relay and the main SMPS transformer.
Third Photo: Main SMPS transformer close up.
Fourth Photo: Looks like an magnetic insulation device, used to protect the SMPS chopper logic from the main transformation circuitry (nowadays this thing is replaced by an little small silicon optocoupler)
Fifth and Sixth Photos: Output filtering coils.
Now, where’s the prize? 😉
Yes, it’s a multi-output power supply. I think it does +12, +5, and -12V at least, and maybe one other. I’m guessing the relay is for the soft-power functionality, so the PSU can be turned off through software, and turned on with a momentary push switch.
Any idea why everything’s covered in hot glue?
Hot glue or other gunk is often used to stop things resonating. The SMPS will oscillate at a certain frequency and sometimes this can get transformed into mechanical energy. That’s why some SMPS based PSUs emit those nasty whining noises. Sometimes a glob of gunk can help dampen the vibrations.
(I’d concur that the big “oil” thing is probably a transformer.)
The glue stuff seems pretty common. My Mac TV and Color Classic both have it all over the analog board holding things in place.
glue is mostly for mechanical rigidity, big heavy components can easily snap off the board when exposed to sudden force vector – user throwing product around
Hot glue is also used to insulate the components against vibration in general to avoid fatiguing the pins and having the components fall off.
raijinzrael got the rest 🙂
And yes, the relay is for the soft-power functionality – there’s a 5v rail that is energized as long as the PSU is plugged in, which is used to power the soft-power circuitry on the motherboard, which then pulls a control line on the PSU to ground (i believe it’s pulled to ground, may be different in old Macs like this, might be pulled to +5v) to turn the rest of the PSU on. Again, in modern PSUs, this is replaced with some silicon switching hardware. The always-on rail is usually referred to as +5VSB in PC PSUs and later Mac PSUs (such as the one from an LC II) – +5v Standby.
The white cased things are likely signal transformers used to feed control information from the high voltage side of the PSU to the low voltage side and/or vice versa, as raijinzrael mentioned in modern PSUs this is replaced by optocouplers and the like, or a much smaller signal transformer. The smaller transformer on the right of the first image with arrows in it is a transformer, and probably the one used to power the standby rail. In old PSUs like this, the standby rail is usually 5v at maybe an amp at most, and a simple linear power supply for reliability and cost-effectiveness. In newer stuff it’s more akin to a USB charging brick’s SMPS setup.
The big black wax paper thing on the left, as everyone has said, is definitely a transformer, the posts at the bottom give it away(it’s where the winding connect to be soldered to the board).. Plus the other give away is the part labeling on the board T101…..
For the little white things are also transformers, their giveaways is the part number on the top is almost identical to the large black transformer….
Nothing new said here, but different way to identify components.
A list of capacitors that need replacing can be found on this web site:
http://www.maccaps.com/MacCaps/Capacitor_Reference/Entries/1990/10/5_Macintosh_IIsi_Sony_Power_Supply.html
The white glue stuff is solastic, used to keep things from moving that shouldn’t move. Be it in shipping (to keep components from shearing off when the unit is dropped) or in use (keep the whine bearable)
The big “oily” transformer is the main switching transformer. It looks odd because, unlike newer stuff (which uses yellow tape), the transformer has been wrapped in paper and dipped in hot lacquer. The two white towers are either regulation feedback transformers, or driver transformers for the switching transistors.
The “transformer” on the right in second picture, the one with the open coils, is a common-mode choke. It’s part of the EMI filter.
Hello,
BTW, can anyone identify the capacitor at C106, on the Sony IIsi power supply? It’s not listed on the maccaps.com page or anywhere at all.
Thanks!