Yes, good point. I spent so much time on this, that doing this first would make sense. I actually enjoy reading those schematics and trying to make sense of it, and how everything works, that I feel it has not been a waste of time. My undergraduate electrical engineering 101 class is now starting to come back to me.
The various input to the PS (5V sense, On/Off, line sense, current sense, power fial, shutdown etc....) and how they all interact with the PS function is still something I am wrestling with, and I have not yet find a way to test the full functionality on the bench. I will try to find a way to load the 5v output (a 1 ohm, 5W power resistor is what I have in mind), feedback the voltage back to the PS on pin N.
From: lincoln.roop_at_email.domain.hidden
Sent: Wednesday, October 01, 2014 2:27 PM
To: lisalist_at_email.domain.hidden
Subject: Re: I blew it - literally
Totally random thought, but to me it seems odd that just opening the door while the machine is on would cause permanent damage. It's possible you shocked the machine with static electricity and damaged something, but one thought that occurred to me: Try checking the safety switch itself to make sure that it is OK - IIRC the rear safety switch is built into the power supply and soldered to the board, make sure that when you press the switch you can see the circuit make using an ohmmeter, and also make sure that when you put the rear door back on and tighten the thumb screws that you actually hear the safety switch click on.
On Saturday, September 20, 2014 1:38:04 PM UTC-4, pintoguy wrote:
So, I had a perfectly good Lisa 2/10 which I had fixed earlier (I had a short in the widget fan). Then, as I was demo-ing it to a friend, I made the mistake and opened the back cover while it was turned on. As expected, the safety switch tripped. The problem is that, since then, the Lisa won't power up. I checked that the 5V standby is there, and I also checked that I get the 18V and 170V DC in the power supply. When the PS is connected in the unloaded state, I noticed that resistors R2 and R33 and hot, but this might be normal,, as the schematics tell us that they will be dissipating about 0.5 W at idle (170V in 51kohms dissipates 170x170/51,000=0.5W). However, resistors R4, R5, R7 and R8 are also very hot to the touch. They are, from what the schematics say, part of the push-pull switching regulator.
Would anyone be able to help me ?
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