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Does anyone have a spare Lisa motherboard?
patrick:
There is an auxiliary video output on the back of the machine. That will not work with any known monitor type due to its weird line frequency, but you can check with an oscilloscope whether video is generated at all.
Next step, check both sync signals sent to the video board. Without HSync the flyback circuit is not running, therefore the screen remains dark. Nevertheless you should see the heater glow, it is getting 12V directly from the PSU.
Check all supply voltages for ripple. Replace capacitors if the ac component is too high, but leave them alone when ripple is still in spec. Electrolytic capacitors from the '80s sometimes fail, but most of them are still in excellent condition today. Parts from the '90s are much worse (leaking etc), and today's stuff lasts exactly until your warranty has expired.
Best idea: find someone living close to you who is able to check your I/O, CPU and RAM boards with his/her machine. Then you can be sure that all issues are located on the mainboard or video section.
AlexTheCat123:
I reflowed the entire video board and I get something on the display now! The first time I turned it on after the reflow, the screen was bright and it displayed an error code of 49. The second time, there was no error code. The third time, however, the screen started out bright and suddenly dimmed to the point that I can barely read it, even with the lights off. I played with all of the potentiometers, but I can't get it any brighter. What happened?
rayarachelian:
--- Quote from: AlexTheCat123 on November 17, 2019, 07:42:23 pm ---I reflowed the entire video board and I get something on the display now! The first time I turned it on after the reflow, the screen was bright and it displayed an error code of 49. The second time, there was no error code. The third time, however, the screen started out bright and suddenly dimmed to the point that I can barely read it, even with the lights off. I played with all of the potentiometers, but I can't get it any brighter. What happened?
--- End quote ---
So 49 is not a good thing, it indicates A or F line trap, this shouldn't ever happen with just a plain boot ROM - might happen if it tried to boot off a hard drive with bad code on it, but not from the ROM, so there might be issues somewhere else on the CPU board, or the ROM is bad. You did say you have a scope, right, you might want to hook it up between the normal +5V and GND rails on the CPU and see if the 5V line is clean or if it drops out or is noisy - this would indicate power issues - though there should be a filtering cap near the CPU to prevent that. You shouldn't be randomly seeing A or F line errors like that. Something is up with the CPU board still. I'd guess maybe it's a contact that's still marginal from the motherboard corrosion and unlikely to be power, but who knows.
It's also possible that something on the analog video board just burned out, but keep power cycling it after waiting a few hours to allow the caps to drain and see if it comes back or not. If it comes back, it's likely a marginal capacitor. It could be as simple as one of the trimpots, or the brightness control in the back not making good contact, they do go bad over time or wear out. Could also be that one of the fixed cracked solder joint cracked again or a trace is somewhat broken and moving the board fixed it, but heat expansion from being on caused it to separate again. Could also be a transistor that's being used as a brightness amplifier gave out?
Lisa2:
--- Quote from: AlexTheCat123 on November 17, 2019, 07:42:23 pm ---I reflowed the entire video board and I get something on the display now! The first time I turned it on after the reflow, the screen was bright and it displayed an error code of 49. The second time, there was no error code. The third time, however, the screen started out bright and suddenly dimmed to the point that I can barely read it, even with the lights off. I played with all of the potentiometers, but I can't get it any brighter. What happened?
--- End quote ---
A common failure point for the Video board, is the 7824 voltage regulator at U1. Usually when it goes it cooks the 120 Ohm resistor R1 near the R2 (width) pot. Look closely at R1 and see if it's is discolored ( you can see R1 without removing the board ). If U1 is bad there will be no power to the flyback transformer..
Rick
AlexTheCat123:
Success! I found a few solder joints on the video board that I forgot to reflow and I also found a few more traces that I forgot to patch on the CPU board. I now have a bright and stable picture and the Lisa shows the TESTING... screen and puts checkmarks over all of the components. However, I feel like it completes the test a bit too fast. It gets through the entire test in about 10 seconds, which seems a bit too fast, even though I only have 512K of RAM installed for it to test. It does not show the ROM version in the corner of the screen like I think it is supposed to. After this, it goes to the Startup From... menu and I can use the mouse to select an option. However, it displays two floppy drives in the menu, even though I only have one. If I select the second drive, it attempts to boot from disk and then promptly ejects the disk since there is nothing on it. The weird part is that it shows a picture of a Twiggy disk with an X over it along with the Error 23 (disk not readable) instead of a 3.5" disk. Given these strange occurrences, do you guys think that I have the wrong ROMs installed? They do have a handwritten marking on them that looks like a C, which makes me think that these are revision C ROMs that only work with Twiggy drives.
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