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Many people use an ATX extension cable to be able to power the board outside of the chassis for diagnostic work, that might eliminate the need for the RGB->HDMI dongle, though I do see how that would be a nice setup.

I plugged in a stereo headset, the sound comes out of both sides, and does not come out of the internal speaker at all while the headset is plugged in.

Good question, I put the machine away but I'll check tomorrow or the next day.

I have done both, same results. I first bodged term power from the external DB25 to the internal connector, then removed the bodge and powered the MacSD through the mini-USB plugged into a wall adapter. Edit: I'm not sure if it is relevant, but I also do not get this sound if I am using an...

Do you have any thoughts on why this only happens with my MacSD, and not with a hard drive? With a hard drive hooked up if I put my ear right up to the speaker I can hear the same noises but very, very quietly. They are only loud with the MacSD.

These are the caps I used (link). The ESR for these is 30 mOhms, This seems low compared to the 800 mOhms of these tantalums (link) that seem to be the go-to for most recaps, but I know very little about caps.

Thanks for the info, I'll look up the caps I ordered. Is this something that could be caused by cap electrolyte that wasn't thoroughly cleaned? I scrubbed the board with IPA and a toothbrush, and I think this one soaked in IPA for a while too, but it didn't go into an ultrasonic cleaner.

Ok good to know, thanks, I didn't really want to deal with cutting up the USB cable.

No, no bodges, the only thing I had to fix was small breaks between the trace/pad on the ALS245 closest to the cap by the power connector.

Yes, recapped with polymer caps.

Yes, the sound also happens/varies when there is no SCSI activity, like just moving the cursor.

Here is a video I took with my phone, if you turn the volume up you can hear the noises pretty clearly. The buzzing sound at the beginning is what I hear when moving the mouse around, then the noises after that are a result of opening a couple folders and opening the Apple menu.

I just installed a MacSD internally in my IIsi and have some strange audio interference. The speaker makes noises corresponding with SCSI/CPU activity. It is hard to describe the noises, but it is like a combination of squeals and clicks. The noises line up with the SCSI activity, and moving the...

I did this and it was effective, however I was only getting 4.1V for term power at the MacSD. It worked fine, but I don't know if it is ok to run it on voltage that low. I scrounged an old USB2 -> mini USB that I am going to splice into a Molex connector to pull 5V internally. I am having some...

Good to know, thanks! I had decided not to get one based on the compatibility info on their site, I'll definitely reconsider.

Here's a pic of my adapter and 40mhz card, I use the same adapter with my 50mhz card.

Good to know, thank you, that header diagram is helpful. You use an external source to power the MacSD USB port in your IIsi? Or you tap into 5V internally and feed it to the MacSD USB port?

I have one in me SE/30 and it works great, I think I have the original DayStar adapter. The Rominator II page specifically says it is not compatible with the PowerCache. https://www.bigmessowires.com/mac-rom-inator-ii/

Thanks for the info.

Is it possible to bodge termination power to the SCSI port on an IIsi? I have a MacSD, they do not have a berg connector to supply termination power.