paul
Veteran Member
Gidday people,
My winter project has been to investigate if it's possible to convert several 110VAC-only items in my much-loved IBM collection to run on our country's unforgiving 230 VAC mains. I dislike modifying things from stock but will do so when the chance of an accident is significant.
I've tackled the 5151 mono monitors first as it's by far the easiest, and at a guess probably one of the very few CRT monitors ever made that uses a line-frequency power transformer. In fact, once past the grossly-inefficient linear voltage regulator circuit, the monitor runs entirely on 15 VDC at 870 mA, a mere 13 watts!
The first step was to purchase a suitable switch-mode power supply to replace the transformer and regulator. The best I could find is a Lambda 26W 15V @ 1.7A, Digikey part number 285-1885ND, at only US$17.50. Even in NZ it was a bargain at $23.50 and I got (2) shipped free by piggy-backing on our weekly order at work.
I removed the power transformer and the incoming AC terminal strip and fuse, just clipping off the line cord connections. The transformer output terminates in a plug on the main PCB, easily removed, as is the connection to the remote TO-3 style regulating transistor - which I left physically in place. As it presents a short to external DC, you'll also need to extract the 7815 three-terminal regulator from the main PCB, desoldering and removing the screw from the heat sink. Easy, when there's no RoHS involved.
By complete luck the threaded mounting holes on the switcher exactly match two of the open holes where the transformer was located. I used one M3 screw from the AC terminal strip and a shorter M3 screw at the rear-most hole to secure it. Naturally you have to ensure the screw ends don't touch anything internal to the switcher. The AC line cord had to be moved in slightly within the strain relief clamp and wired with crimp-on terminals as shown in the photo. The ground on the switcher is provided via the mounting to the plate, no wire required. The connection to the PCB is equally simple, see the photo, brown is +15V. All that's left is to check the output is 14.9 to 15.0 V and screw it back together.
My winter project has been to investigate if it's possible to convert several 110VAC-only items in my much-loved IBM collection to run on our country's unforgiving 230 VAC mains. I dislike modifying things from stock but will do so when the chance of an accident is significant.
I've tackled the 5151 mono monitors first as it's by far the easiest, and at a guess probably one of the very few CRT monitors ever made that uses a line-frequency power transformer. In fact, once past the grossly-inefficient linear voltage regulator circuit, the monitor runs entirely on 15 VDC at 870 mA, a mere 13 watts!
The first step was to purchase a suitable switch-mode power supply to replace the transformer and regulator. The best I could find is a Lambda 26W 15V @ 1.7A, Digikey part number 285-1885ND, at only US$17.50. Even in NZ it was a bargain at $23.50 and I got (2) shipped free by piggy-backing on our weekly order at work.
I removed the power transformer and the incoming AC terminal strip and fuse, just clipping off the line cord connections. The transformer output terminates in a plug on the main PCB, easily removed, as is the connection to the remote TO-3 style regulating transistor - which I left physically in place. As it presents a short to external DC, you'll also need to extract the 7815 three-terminal regulator from the main PCB, desoldering and removing the screw from the heat sink. Easy, when there's no RoHS involved.
By complete luck the threaded mounting holes on the switcher exactly match two of the open holes where the transformer was located. I used one M3 screw from the AC terminal strip and a shorter M3 screw at the rear-most hole to secure it. Naturally you have to ensure the screw ends don't touch anything internal to the switcher. The AC line cord had to be moved in slightly within the strain relief clamp and wired with crimp-on terminals as shown in the photo. The ground on the switcher is provided via the mounting to the plate, no wire required. The connection to the PCB is equally simple, see the photo, brown is +15V. All that's left is to check the output is 14.9 to 15.0 V and screw it back together.