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[AlexTheCat123]

I bought a Lisa late last year and got it fixed up with the help of the members of this community (see the topic "Does anyone have a spare Lisa motherboard?" for details), but it has unfortunetely started having problems again. The image on the CRT started scrolling a few months ago, but it was still somewhat usable because the scrolling was so slow. A few days ago, however, the problem got worse. Now the picture's vertical height is very jumpy and it randomly changes height while the Lisa is running.
Most of the time, there is only a single horizontal line on the display, but it will occasionally enlarge for a few seconds before returning to the horizontal line again. You can see the scrolling issue and some slight vertical jumping (although not nearly as bad as it is now) at about 4:58 in this YouTube video that I made about the computer: https://www.youtube.com/watch?v=6hStH5EwmfY. Do you have any ideas about what may be causing this issue? I have already tried playing with the potentiometers on the video board and they don't seem to be helping at all.

[stepleton]

It seems likely that there is a fault on the video board. I suppose this is obvious...

I don't know the answer here, but for problems like these, you may benefit from reviewing the video diagnostics advice for compact Macs in The Dead Mac Scrolls. This book isn't about the Lisa, but generally the parts and problems that it talks about have direct analogues on Lisa video boards. You may need to look at schematics to identify which Lisa components are the same as the Mac ones, but since the book calls out specific components and explains what the components do, it may not require too much detective work.

[rayarachelian]

So that sounds like the vertical hold pot on the power supply, gently wiggle that guy while the Lisa is off it might help clean it. If not it might be some other thing on the analog video board behind the CRT such as the two trimpots in the FAQ answer or the coil in the middle.
see:

* https://lisafaq.sunder.net/single.html#lisafaq-hw-vid_jumpy
* https://lisalist2.com/lisalist1/3505.html and associated replies in the LisaList1 thread

[8088mph]

I had a similar problem, the picture was bouncing up and down but it was not scrolling like yours. I had to change three 16V 10uF capacitors on the analog video board. Take a look at the video board, if you can see corrosion from leaking capacitors, you should definitely change them. The potentiometers are another common problem, you can use contact cleaner on them or change them.

[AlexTheCat123]

I had to change three 16V 10uF capacitors on the analog video board. Take a look at the video board, if you can see corrosion from leaking capacitors, you should definitely change them. The potentiometers are another common problem, you can use contact cleaner on them or change them.

Thanks for mentioning this! After looking at the capacitors, I noticed that they are bulging and probably need to be changed. I'll buy replacements in the next few days. I accidentally broke the vertical hold potentiomenter when reflowing the board (reflowing it didn't fix the problem) so I'll need to order a new one. Can anyone recommend a good replacement potentiometer that will fit in the board?

[8088mph]

I got my pots from someone else. I can ask if you can't find any. They have different values so make sure you get the right value for the particular one you are replacing. If you want original parts, I still have mine, they probably work fine since the capacitors ended up being the problem but I had changed the potentiometers first.

[AlexTheCat123]

If you want original parts, I still have mine, they probably work fine since the capacitors ended up being the problem but I had changed the potentiometers first.

Thanks for the offer for the pots, but I already ordered a new one (Bourns 3352T-104LF) along with all of the electrolytic capacitors needed to recap the video board before I saw your message. I hope this fixes the problem!

[AlexTheCat123]

The new capacitors and trimpots for the video board arrived today. I installed all of the capacitors and replaced the Height and VHOLD potentiometers, but the problem is still there. I can barely see it since the screen is just a horizontal line, but I think that replacing and adjusting the VHOLD trimpot has stopped the scrolling issue. What should I try next to solve the horizontal line problem?

[stepleton]

I would recommend checking out some of the additional advice from The Dead Mac Scrolls, linked above in my previous reply. I've seen one or two video boards fail owing to bad semiconductor components---while caps and pots are well worth replacing, the board lives in a cramped, dusty, perhaps hot little space and gives a hard life to its other parts too. The Mac analog board video circuitry is similar enough to the Lisa video circuitry that the advice can carry over, provided you can identify which Mac components are analogous to which Lisa components.

[patrick]

The new capacitors and trimpots for the video board arrived today. I installed all of the capacitors and replaced the Height and VHOLD potentiometers, but the problem is still there. I can barely see it since the screen is just a horizontal line, but I think that replacing and adjusting the VHOLD trimpot has stopped the scrolling issue. What should I try next to solve the horizontal line problem?

Check the vertical deflection circuit. This is U2 (TDA1170N) and the components around it.

There is a LM7824 voltage regulator on the board. At its output (pin 3 or C2) you should measure +28 V. The voltage can be adjusted with the pot labeled "WIDTH". Do not apply more than 30 V here, otherwise the TDA1170 could be damaged. If pin 1 and pin 3 of the controller indicate almost the same voltage value, the width potentiometer is defective. C2 could be worth a replacement, it is heavily used. But I assume you have already done this.

At pin 2 of the TDA1170 (or at C12) there should be 11..16 V. R24 is getting really hot, it drops the difference between the +28 V supply and this voltage.

At pin 8 you should see (or hear) the 60 Hz VSync from the CPU board. If this is intermittend, you have issues (corrosion?) with your mother board. or with the CPU board / video PROM.

Pin 4 drives the vertical deflection coil. Check the solder joints at the connector, and check (or replace) C19 with a low ESR/high ripple current rating capacitor. It is in series with the deflection coil and carries its full current.

If the width regulator or voltage regulator has failed in the past, your TDA1170N may be flaky. I had to replace this part quite often.

[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]

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?

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?