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Apple Lisa power supply / PSU whine

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    Apple Lisa power supply / PSU whine

    Hi all,

    I've recently managed to get hold of an Apple Lisa 2 in pretty nice condition, including an external 5MB Profile in working condition. I have one issue with it though: The Lisa power supply emits some whine or buzz that seems to modulate based on load. Changing the screen brightness or contrast changes the frequency, as does system activity like starting programs. I've taken some videos that include the sound, and pictures of the PSU in this album:

    The seller said that all Lisa PSUs are noisy these days, which I can believe given that the age of the units these days. But I am concerned that this might be indicate of an upcoming, preventable failure. The seller is offering to swap the PSU for a different, quieter one, but I'd like to understand the problem better before stepping into action here.
    • Could this be a side effect of aging caps? While the unit was offered as recapped, the capacitors on the PSU seem original (including cracked RIFAs).
    • Since I cannot run the Lisa off the PSU without having it fully inserted in the case, I cannot exactly make out where the noise is coming from. Could it be the marked component in this picture (not mine, forgot to take a good picture when I had mine open)? Is that some sort of regulator?
    • lisa-psu-marked.jpg
    • Do you think it's safe to operate the Lisa with that issue present? I see that the pixels on the screen are "dancing" slightly (visible in the video, scanlines are not in perfect horizontal alignment).
    • It's a 120V 1.2Amp PSU running on a 230V->120V step-down converter (product link). Could that be creating line noise that the Lisa amplifies? (Converting the PSU to 230V would rule that out, but that might be a topic for a different thread. )
    Thanks for any advice you can give. Happy to provide any additional information that might be helpful!


    I would always be suspect if you are saying it was sold recapped and it wasn't when it arrived. I might want to raise a case on that with the seller before digging into the PSU.
    It could be coil could be a dirty PWM for chopping on the main transistor.
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      I have a Lisa 1.2A power supply like yours that is also noisy. I haven't investigated why this is so, but changes to the sound that depend on computer activity are typical. The PSU has worked for hours inside the computer without trouble, but all of the noise makes it a backup for my other PSUs, which are quieter (although my other 1.2A PSU is not 100% silent, either). One day I will investigate what's going on.

      Having used my "loud" PSU in a 120V 60Hz country and now in a 240V 50Hz country, I can say with confidence that the audible noise in my PSU has nothing to do with the local line frequency. Additionally, recapping the PSU didn't affect the noise in my case.

      The part you've identified is the main switching transistor, which is what pumps a high-frequency alternating current into the adjacent transformer. In a certain sense that's more poetic than precise, it's the "beating heart" of the PSU. It's what's doing the "switching" in a "switching power supply" like this one. Unlike a real heart, though, it's probably not making any noise.

      What I've assumed is the problem with my power supply, and what I might assume is wrong with yours, is that the wires or the metal plates within the transformer are buzzing at some frequency relating to that switching current. Transformers work by trading electrical and magnetic energy against each other, and all of that magnetism can wiggle transformer parts that are loose. This is what NeXT meant by "coil whine". If this is what's going on with your device, it's probably not a all that big deal from a safety perspective, but it's probably also somewhat difficult to fix.

      Your PSU does not look at all recapped. In my Lisas, recapping does help with "dancing" scan lines, but you may also want your Lisa's video card serviced instead of / in addition to the PSU. I know it's less fashionable these days to recommend a recapping, but I have found recapping the video board to be specifically helpful.


        PS: You've noticed in your photos that the Lisa has two transformers. The smaller one is for the +5V standby voltage and is not responsible for the sound. We know this because this power supply always operates when the Lisa is plugged in to power, and we don't hear any buzzing until you turn the Lisa on. So the problem must be in the "main" power supply.


          It is a really interesting and not often talked about area, the cause of whine or noises that are emitted from the components in switching supplies.

          There are the obvious causes for it as mentioned magnetic materials under the influence of varying magnetic fields and vibrating the adjacent air molecules and acting like a speaker, or even coil turns which have magnetic forces on them when they carry a current and generate a magnetic field interacting with an external field to put forces on the wires.

          However, there is another cause for the noises:

          It is the Piezo electric effect, of an object changing its physical geometry with applied voltage (this includes capacitors and semiconductor crystals). This physical movement also generates sound and is the Electrostatic version of the Magnetic problem. How common is it ?

          Well much more than you might think. Some years ago I built a switching supply devoid of inductors. The mosfets switched a square wave into a bank of capacitors. The mosfets themselves generated noise. The effect is much better observed with a vintage TO-3 transistor. If you set one up as a 100Hz switching supply, with fast rise and fall switching, you can hear the transistors "singing", yes that is right, they generate sound. It is damped a little when they are screwed to a heatsink, but it is still there. Also when film capacitors are rapidly charged and discharged the effect is possible too. I found that epoxy cased transistors were a little quieter than TO-3 types, presumably due to the additional damping from the epoxy. Possibly with large pulsatile track voltage, even a pcb could act like a piezo-electric speaker.

          Recently I have been working on a pwm motor speed controller for a lathe, it has a 1kHz pwm rate and it switches full wave pulsed 100Hz DC across the DC brush motor with a large power mosfet. The motor itself of course makes an excellent "speaker" but the board sounds like a small orchestra with a number of the board's components generating sound.
          Last edited by Hugo Holden; October 27, 2021, 03:22 PM.


            Bad capacitors can cause PSUs to whine, but they generally need to be very bad, like shorted or open.


            Like in this case, both main line caps were bad. One was a dead short and the other one was only like 20% of its rated capacitance.


              Thanks for the detailed replies, everyone; I've learned a lot!

              I'm glad to hear that the noise likely is only that, noise. While it's a bit annoying, I can well live with it knowing that it's not some component that's screaming in agony.

              I will still raise the issue of the PSU not being recapped with the seller. From peeking inside, the video board looked better to me. I've added a picture to the album: I have recapped some 80s PCs power supplies in the past which had completely failed, so I'm not out of luck if the conversation with the seller doesn't go well (so far, I don't have any reason to believe that's going to happen). But let's hope it doesn't come to that, as my craftsmanship certainly still has room for improvement.

              stepleton, since you mentioned using your 120V PSUs in a 230V country now: did you convert the PSUs themselves, or are you using external converters? What I found in the Lisa hardware manual suggests that I only need to change a single jumper wire near the rectifying diodes, but I'm sure that I'd need to use a different fuse and possibly line filter caps for a higher voltage. I'd like to get rid of the external converter once I got the recapping sorted out with the seller.

              Again, thanks for all your help! I'm already feeling much better about using the Lisa in its current state.



                If the seller replaced caps, I'm not seeing where. Did the new caps come pre-dusted with vintage dust to keep the vintage look and feel?

                Every cap I see looks old. Nichicon doesn't even make the SE series anymore, and hasn't for a very long time. Most of their modern caps have three letter series names like UZW, UPG, etc. Same with Nippon Chemi-Con, the SL series is ancient and I don't think they've had orange sheathed capacitors for decades. The only time I ever see those is in 25+ year old equipment. If you want proof, just look at the solder joints, you'll see some evidence of them being removed and replaced if the seller did anything. But the dust is more than enough to know nothing was done, any competent repair tech is going to clean the PCB and components if they have them out of the machine, and new capacitors don't come pre-dusted.

                If you bought the machine from a marketplace with buyer protection, I'd make a stink about it. A cap kit for that machine will easily set you back $40-50, and potentially more if you have to substitute out EOL caps for something else. The seller could have lied about recapping it to sell it for more money, because most people know if old gear like a Lisa isn't recapped, it's going to have issues.


                  Originally posted by GiGaBiTe View Post

                  If you bought the machine from a marketplace with buyer protection, I'd make a stink about it. A cap kit for that machine will easily set you back $40-50, and potentially more if you have to substitute out EOL caps for something else.
                  Whaaaa? From where?? When I recapped my 1.8A it was less than $20.
                  [Need something to waste time on? Click here to visit my YouTube channel CelGenStudios]
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                  = Excellent space heater


                    Originally posted by mikerofone View Post
                    stepleton, since you mentioned using your 120V PSUs in a 230V country now: did you convert the PSUs themselves, or are you using external converters? What I found in the Lisa hardware manual suggests that I only need to change a single jumper wire near the rectifying diodes, but I'm sure that I'd need to use a different fuse and possibly line filter caps for a higher voltage. I'd like to get rid of the external converter once I got the recapping sorted out with the seller.
                    I use an external step-down autotransformer. My Lisa stuff includes some printers and some ProFile hard drives that are all 120VAC, and rather than change everything to be at the local line voltage, it's easier to keep the entire ensemble as a tiny bit of North America here in London.

                    Beware that there are two kinds of Lisa power supplies: the 1.2A Apple PSU from your Lisa 2/5 and the 1.8A DataPower PSU ordinarily found in Lisa 2/10 systems. The process for converting either between 120VAC and 230VAC is different. I haven't attempted it on either kind, so I don't know the specifics, but do make certain that your instructions are for the correct device!


                      Thanks for the warning about the different PSU types! I will double check that I have the service manual for the correct PSU before attempting anything.

                      The seller admitted that they didn't recap, and claim that they "forgot to update the description" from a previous Lisa they sold. Since they are a serial seller of Lisas and have tons of videos of other pristine vintage gear on YouTube, it could be true. I would have haggled more though, if I had known...

                      That aside, aside from the slightly wobbly image, everything is working pretty well. Should I replace all caps right away as they could start leaking and damaging things? Or is that not a common issue since the caps are old, but super high quality? I think I know the answer, but maybe....

                      Cheers mikerofone


                        Well, you certainly should not delay with the RIFAs, particularly since with this design of power supply they could pop off anytime the computer is plugged in. And as long as you have the thing open and on the bench...

                        It's now been a few years since I recapped my PSUs and I think I do remember one or two of the caps having a little smudge of sauce underneath when I did a shotgun recap, which was the style at the time. It wasn't all of them, but one or two.

                        At some point your video experience is likely to degrade further --- from my perspective this seems to be a fact of Lisa life. When it does, and assuming it's just more of the wobbles and not a dramatic failure (e.g. complete vertical collapse), the most likely suspects in my experience will be (a) PSU caps (b) video board caps (c) the video board potentiometers (which you can try hitting with some contact cleaner; it might help). You may decide that you'd like to replace the PSU caps now just to spare yourself some hassle isolating the problem later on.

                        But that is the kind of thing that a mediocre diagnostician like me would say. Talented folks who start off sentences with "if you really want to learn electronics" might advise you to leave the caps alone so that you can try dealing with the whole challenge later. After all, there is no school for learning this stuff quite like an open PSU with hundreds of volts of post-rectifier DC just inches away from your fingertips.
                        Last edited by stepleton; October 28, 2021, 02:41 PM.


                          Originally posted by NeXT View Post

                          Whaaaa? From where?? When I recapped my 1.8A it was less than $20.
                          Hah, maybe 10 years ago.

                          Capacitor prices have skyrocketed, plus shipping, online sales tax and customs import fees if you order from Digikey from the states. I remember the good old days where recapping a power supply was $20, those were good times.

                          The only way I'm getting $20 recaps these days is ordering sketchy caps from China on Ali Express that were probably dumpster dived in Huaqiangbei or Shenzhen.


                            Hey folks,

                            I appreciate all the input. I've spoken to the seller and they are sending another 1.2A board which they say is quieter, and which has had at least one "RIFA" replaced (they mean the white capacitor right next to the cracked orangey one in this picture). I didn't even notice that this is a capacitor - do these blow up as well? They will include a new orange RIFA and the potentiometers mentioned in stepleton's comment #12, so I can change them myself. I was surprised to hear that the potentiometers could be an issue. I'm familiar with scratchy pots, but I'd have thought that wiggling them and applying some contact-cleaner should fix whatever corrosion might have built over time. It's not as if these were regularly adjusted and thus worn out, I would think. Can you elaborate on what makes them degrade over time?

                            In speaking to the seller I learned that the two of us have a different philosophy on changing the caps. They only change them when they notice signs of failure, but for something valuable like the Lisa, I'd consider doing a preventative full recap to avoid any corrosive gooey surprises. At the same time, I'm not too convinced of my own desoldering skills that I'd be sure that I'd fix more than I'd break.
                            The seller did do some long-term testing though, i.e. started the Lisa many times over the course of weeks and let it run for hours to ensure that nothing blows up. So it makes sense that they wouldn't simply go through the ordeal of changing all the caps since they were going to sell it anyways. To their credit, they offered to take it back and refund me, but I declined. Even if not recapped, the price seemed OK for a fully working (at least for now) unit with all peripherals and a working ProFile. (Side note: I noticed people rarely mentioning the prices for expensive retro stuff they bought. I'm happy to disclose what I paid, but I wonder whether not documenting these prices permanently in forums like this one is a way to not give people a reason to ask for too much? In the end, it was the most money I every spent on a single computer, be it retro or modern...)

                            In the end, I'm still happy with my purchase, and I'm happy to have learned that the noise is not a reason to worry. I'm hoping that the new PSU will be quieter, and I'll inspect and probably change the caps there as a preventative measure. Thanks again for all your valuable advice!

                            If I attempt the 120V->230V conversion of my PSU, I'll create a new thread to share how it went.



                              The white capacitor is indeed a mains filter capacitor (note X2 class designation on the package; here's what those designations mean) and it accomplishes the same thing as the RIFA caps that you may also find in those locations. I have only known RIFA mains filter capacitors to fail in the manner and frequency that RIFA caps do.

                              Note that the potentiometers I was referring to were not the ones on the power supply; instead, I mean the six trimmers you find at the top of the video board inside the computer --- so, not in the power supply at all. Here's a thread where someone ran into exactly the sort of problem I was thinking of, although that same bank of trimpots can cause other problems, too, depending on which ones are misbehaving.

                              Back on the power supply --- it's interesting (maybe) that the two potentiometers there have nothing to do with the rest of the power supply at all: if you look at top right of the schematic, you can see that the bit of circuit connected to pins 1, 3, 2, B, A, and D isn't connected to anything else. The Lisa design just places CRT focus and brightness adjustment there for user convenience and probably safety as well (note that there is a 400V potential between pins 1 and B, and the PSU is already a part of the Lisa designed to contain high voltages). It's a completely separate system.

                              As you will basically be receiving a replacement power supply, this could be a good opportunity for you to determine whether the video problems you've observed are more likely the fault of the video board or the fault of the power supply. If you notice a substantial change, then the power supply may have been responsible. If you don't notice any change, then the video board could be the main culprit.