68kMLA Classic Interface
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| 2 Analog Boards: LF2 with & without Earth Ground | |
| Posted by: JDW on 2020-03-06 01:30:05 Below are 2 photos of AC line filter "LF2" from two different Macintosh 128k~Plus Analog Boards. The newest board is stamped 4192 (1986 PCB), which I assume means 42nd week of 1992, and uses the LF2 without the green Earth wire. The other PCB is a 1983-84 version stamped 0792, which I assume means 7th week of 1992, and you can see it has the green earth wire wound inside LF2. Indeed, most every Analog Board I've seen has the Earth wire wound in LF2. Why do you think the green Earth ground wire was not wound into LF2 on the 4192 board?   By the way, the 3-pin power connector mounts those 3 pins to the PCB, but the Earth pin has no PCB trace. Regardless of which board we look at, the Earth ground coming from the power cord screws down to the metal chassis, so the chassis is Earth grounded. It's simply a matter of why that green Earth wire does or does not go through LF2 that I am curious about. Search this PDF for "LF2" as a keyword to see the schematic which mentions that it does indeed go through LF2. Hmmm... | |
| Posted by: JDW on 2020-03-06 01:43:51 Separately from my opening post above, let me know your thoughts on the LF2 wobble I show in my video below (that's from yet another analog board I own). View attachment LF2.mov | |
| Posted by: cheesestraws on 2020-03-06 04:01:07 That's interesting. I'd have personally thought that inductively coupling your protective earth to your line is an ... interesting choice? I was going to wonder whether the difference in wiring colours suggested a change in regulations around that time somewhere that they were going to be selling those boards (solid green -> green/yellow) but the third board you posted has green/yellow *and* has it wound around the filter. So that's probably completely untrue. | |
| Posted by: LaPorta on 2020-03-06 05:44:17 Is either an international board? | |
Posted by: JDW on 2020-03-06 16:18:13Is either an international board?They are all 120VAC US boards. I actually have a 4th analog board, and on it LF2 has the green Earth ground wrapped along with those other 2 wires. I want to determine if leaving off the green Earth wire in LF2 was a cost savings measure that turned a blind eye to optimal engineering design, or if the ground was left off intentionally for some reason. @Bolle? @techknight? | |
| Posted by: JDW on 2020-03-06 23:12:03 Note that both the Macintosh 128k Analog Board schematic and the SONY PSU schematic (for SE and SE/30) all show the Earth ground in the windings, which again compounds the mystery as to why Earth was left out of the windings of LF2 on that one analog board I own.   | |
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