I picked up a non-working IBM 5154 EGA monitor for about thirty dollars, with the idea that if it couldn’t be repaired I might at least reuse the case. It was rough cosmetically, with Sharpie on the shell, stickers, tape residue, and plenty of wear. When I powered it on, it made a brief CRT “twang” and then shut right back down, so I went straight for the power supply.
Getting inside took a little work. One of the plastic trim pieces cracked, the case screws came loose with that familiar first-open snap, and the power supply turned out to be enclosed in its own metal cage. IBM had also used rivets on the cage, so I drilled those out and made sure to clean away the metal shavings before going any further.
Once the supply was on the bench, the fuse checked good. I found two RIFA capacitors that needed replacement, and one electrolytic that looked much worse once it was removed from the board. It measured around 40 µF against a 2200 µF rating, so that one was completely dead. I pulled and tested the other medium-sized capacitors as well, and the two large filter caps turned out to be fine after checking capacitance and ESR on an LCR meter.
That still didn’t bring the monitor back. I checked the supply voltages and found the 12-volt regulator wasn’t getting what it needed, so I kept tracing through the startup side of the power supply. With help from the schematic and some troubleshooting, I narrowed it down to a bad transistor, marked T6, that had failed without any visible damage. I replaced that transistor, added fresh thermal compound, and the 12-volt rail came back.
With the supply producing proper output, I reconnected it and tried the monitor again. I got degauss activity and signs of life, but still no usable picture, so I pulled the main board. That meant disconnecting the video board and carefully removing the anode cap from the tube before lifting the board out for testing.
On the main board I focused on the hotter areas first, along with the transistors and ICs. I found one bad transistor there as well, replaced it, and then went through the rest of the resistors, diodes, and capacitors before putting everything back together. A later round of power supply checking also cleared up one mistake on my end: the 6.3-volt heater supply used an isolated ground, so I had been measuring it incorrectly until I checked across the proper points.
I replaced the drilled-out rivets with short sheet metal screws, reassembled the monitor enough for another test, and this time it came up properly. Hooked to an IBM 5150, it displayed the EGA BIOS screen, color bars, and games cleanly. I made a small vertical size adjustment with a test pattern and left it there.
The last job was cleaning. Orange oil removed the adhesive residue and even took off the Sharpie better than isopropyl alcohol, while soap and water handled the rear shell and Windex worked for the front. Once it was back together, the 5154 looked right at home on top of the 5150 and was fully working again.
— Aaron
Links
Timestamps
00:00 – Intro
03:07 – First Look
05:05 – Disassembly
10:18 – Removing Rivets
11:52 – The Power Supply
17:00 – Testing Capacitors
22:08 – Test 1
26:18 – Replacing Transistors
31:05 – Test 2
32:19 – Testing The Main Board
33:58 – Test 3
34:44 – Isolated Ground!
39:43 – Test 4
44:08 – Cleaning
47:13 – Wrap Up