I worked on an Apple Monitor II, model A2M2010, that had two obvious problems: a high-pitched whine and a collapsed vertical image. The first power-up showed a very small raster across the middle of the screen, and the monitor also produced an audible tone that was lower than the normal 15 kHz horizontal frequency. The vertical size control never brought the picture up to full height, and moving the composite cable at the back made the image jump around.
Once I opened it up, I discharged the CRT and pulled the chassis out to get a better look at the board. I checked the top side first, then removed the board to inspect the solder side. I didn’t find the cracked solder joints I expected, but I did find signs of earlier rework on the underside. I cleaned the connectors, treated some of them with DeoxIT, and exercised the pots, including the internal adjustments, before putting it back together for another test.
That first round didn’t solve it. The monitor still had the reduced vertical height, and the whine was still there. I did some tapping and listening with a wooden chopstick and found that pressing around the flyback area changed the sound. The noise would come and go as I pressed near that section of the board, but I still wasn’t getting the vertical problem to react to tapping anywhere else.
From there I checked the supply voltages against the Sam’s Photofact documentation. The 47-volt line measured 48.73 volts, B+ measured 12.2 volts, and the 14.9-volt line came in at 15 volts, so the main voltages were where they should be. Since I expected to have the board in and out several more times, I went ahead and modified the two annoying ground leads with inline connectors so I could disconnect them quickly instead of removing the hardware every time.
I then started pulling and testing capacitors. The large 3300 µF capacitor tested fine, but one electrolytic, C205, had leaked underneath even though it still measured close to value and showed low ESR. While desoldering a couple of other capacitors, I found something more useful: one capacitor had only one leg actually connected. I had desoldered a different part and realized this cap was loose on one side, which explained why it moved when it shouldn’t have.
After replacing the leaking capacitor and fixing that loose capacitor connection, I powered the monitor back up and got a full image again. The whining was gone at first, then returned briefly, but the display itself was now stable and filled the screen. I ran through several test patterns, adjusted the vertical hold and vertical linearity, and got the crosshatch and character patterns looking much more even.
I also spent a little time comparing my notes with what ChatGPT 5 had suggested. Its prioritized list of likely capacitors and checks lined up well enough that it would have pointed someone in the right direction on this monitor. It also correctly described the kind of vertical compression I saw from the capacitor in that feedback area.
I finished by adding a standard IEC power inlet in place of the permanently attached cord, then hooked the monitor up to an Apple II Plus. It came up cleanly, displayed a sharp bright image, and ran Oregon Trail without the collapsed vertical problem.
— Aaron
Links
Timestamps
00:00 – First Look
03:03 – Apple Monitor II Test 1
09:55 – PCBWay Ad
10:25 – Disassembly
14:38 – Visual Inspection/Repair Plan
26:32 – Wire Hack
31:02 – Capacitors
35:01 – Test 2
41:05 – Was AI Helpful?
43:50 – Final Result
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