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Apple Lisa Scrolling and Jumpy Display

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AlexTheCat123:
I checked the voltage from the voltage regulator a few days ago and it's right around 28 volts, so I think the voltage regulator and WIDTH pot are fine. I wasn't able to check anything else around the TDA1170N while it was running because it's really hard to probe the chip when it's installed in the Lisa. I'm constantly afraid that I'm going to short something out with my multimeter probe. However, I did pull every component that has to do with the vertical deflection circuit (except for the TDA1170N) out of the board and they all checked out just fine when I tested them. This makes me believe that my problem is with the TDA1170N itself. I bought a replacement off of eBay and it be here on Thursday. You mentioned that C19 should be replaced with a low ESR and high ripple current capacitor, but I already replaced it (along with all the other electrolytic capacitors in the board) with a standard electrolytic capacitor. Is this a problem?

patrick:

--- Quote from: AlexTheCat123 on April 28, 2020, 07:05:45 am ---You mentioned that C19 should be replaced with a low ESR and high ripple current capacitor, but I already replaced it (along with all the other electrolytic capacitors in the board) with a standard electrolytic capacitor. Is this a problem?
--- End quote ---

C19 is in series with the vertical deflection coil and carries ist current. With insufficient ripple current rating the capacitor will fail after some time. As long as it is running cool, use it. If it is getting hot, its power dissipation is too high.

Make sure to get replacement parts from from well-known manufacturers like Panasonic, Elna, Nichicon, Nippon Chemicon, etc and use their longlife series. Most electrolytic capacitors from the '80s are still working fine after 40 years of service life, and many cost-optimized parts from today fail after three years. Sounds crazy, but it is more likely that your 2017 Sony TV needs re-capping than your 1983 Apple Lisa.

AlexTheCat123:
I just got back to working on the project again and things have gotten worse. Now there is nothing on the display whatsoever. I replaced the TDA1170N chip and there was no change in the screen's behavior. I can still see the heater glowing in the neck of the tube, but aside from that, it shows no signs of life. I have probed around on the video board with my oscilloscope and have determined that it's getting all of the signals and voltages that it needs in order to function. However, when I was measuring the voltage in parts of the circuit where the schematic says that it should be getting 5 volts, I got a reading of between 2.7ish and 3.7ish volts, depending on when I measured it. What could be causing this and could this be the problem?

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