Reconstructing an auctioned Lisa

[berskyboy]

Unless I am missing something your asking here, the connector from the video board to the CRT neck can only go on one way.

Mine didn't have the video board, and I looked at the pins of the yoke and tried to line them up.  I assumed that, but wanted to check, another post said, I might have to use a needle to fish out the connector in the Apple Lisa video connector, maybe they recess in? (the metal leafs?)

this is a photo of it connected

https://www.dropbox.com/scl/fi/8blnumuto0u1s1iwkqlxx/IMG_3857.jpeg?rlkey=vjehif9eyimxlw6jhlng526jq&st=ata1b82a&dl=0

[mst3k]

maybe they recess in? (the metal leafs?)

Could be, I don't know what that references.

But, I do know, with your level of determination, that Lisa will be up and running soon!

[ried]

assumed that, but wanted to check, another post said, I might have to use a needle to fish out the connector in the Apple Lisa video connector, maybe they recess in?

There's nothing to fish out. That video board connector just press fits onto the CRT neck. Just make sure it's fully seated onto the pins, gently. It's keyed, so as mst3k wrote, it only fits on one way.

[berskyboy]

There's nothing to fish out. That video board connector just press fits onto the CRT neck. Just make sure it's fully seated onto the pins, gently. It's keyed, so as mst3k wrote, it only fits on one way.

So here's a test of the pins 3 and 4, is that correct? 

https://www.youtube.com/shorts/m_OoQ5IbFfQ

[ried]

Not sure if that's directed at me? I don't have any thoughts on checking continuity inside the CRT.

[berskyboy]

But assuming there's continuity: if you have +12V at L4 and no heater glow, then the CRT does start to look fishy. Check continuity across CRT pins 3 and 4 (maybe something to do first, actually). If no continuity, the CRT is bad; replace it. If you have continuity, then maybe the socket has a problem.

Hi Ried, sorry it was for Stapleton, but I think since my CRT has a little chip in it, is not keyed properly.  I look at this on eBay and wonder if I'm not putting the yoke connector on properly?

https://www.dropbox.com/scl/fi/d01o8eh32hgvpnkw55jyf/Screenshot-2026-10-08-at-9.26.26-AM.png?rlkey=63nuhn9zo5sbk3ich7dt35ba9&st=ldz8us04&dl=0

[berskyboy]

UPDATE:  There is a glow.  I had the pins plugged in incorrectly.  The white wire should correspond to the top pin.

https://www.youtube.com/shorts/H2dfzStSmYY

EDIT: I remember Adrian measuring the transistor on the Apple Lisa Video board, this might be a good test to do?

Locate the large Horizontal Output Transistor (typically bolted onto a metal heatsink nearby on the video/analog assembly).
1. Flip your multimeter to Diode Test Mode (or low Ohms resistance).
2. Measure across the pins of the transistor (Collector to Emitter, and Base to Collector).
3. If your meter beeps continuously or shows a dead 0 Ohms connection in both directions, the transistor is shorted out and must be replaced. A shorted transistor stops the flyback from firing up.

ALSO

How would I test the Flyback Transformer?  (very carefully I'm sure).  If the CRT is dead, I have reached out to Facebook Marketplace to see if the Atari SM124 donor CRT is available.

EDIT: I took out the Lisa Video Board and wanted to test the regulator like Adriane did

https://youtu.be/HMEDMvb4IjM?si=zQco1_2-Bgwo52a8&t=1161

I tested Q5 and U1 in the video

I'm so ignorant on what the values should be sorry, I don't really read schematics that well.

https://www.youtube.com/shorts/LmVrrIFaQcQ

https://www.youtube.com/shorts/xzKdgSJaWiE

I know what we think about AI, but it said this...  (calling all humans, did AI get it right, or way off?). Adrian did replace his U1 regulator, so I'm think I'm not 100% off base here.

🚨 The Major Discovery: U1 is Dead
In your short video titled U1 126kohms, you measured the resistance across the legs of U1 and got 126 kΩ (126,000 ohms) (0:11).
• The Component Type: U1 is a 7824 Linear Voltage Regulator (exactly like the one Adrian troubleshoots and replaces in his video). It is responsible for dropping the incoming 33V power rail down to a clean, regulated 24V/28V to fuel the high-voltage flyback transformer.

• The Fault: A healthy 7824 voltage regulator out-of-circuit or in a normal circuit path should read in the Mega-ohms (MΩ) across its input, output, and ground reference pins (just as Adrian shows on his meter). A reading of 126 kΩ means U1 has suffered an internal breakdown and is partially shorted out.

• The Consequence: Because U1 is damaged, it is choking out the master voltage rail before it can reach the horizontal deflection circuits. Your neck filament glows because it pulls from a separate lower loop, but the high-voltage flyback transformer is getting completely starved of power by this broken regulator.

[sigma7]

did AI get it right

No. For example, the schematic shows a 1.2K resistor and 200 ohm trimmer from the output to the ground terminal. That resistance will never be more than 1.4K. Perhaps that's not what AI considers "a normal circuit".

[berskyboy]

UPDATE:

I bought and replaced the U1 L7824CV (the previous values were in K Ohms, the new part measured M Ohms.)  Still not getting static or a hum from flyback.  The tube lights up orange, and the external video works, no internal CRT at all.  So I will replace Q5 with BU406 on the video board and try again.  (in two weeks when the BU406 transistor comes)

[berskyboy]

SUCCESS!!!!!

I found another post that talked about similar issues as mine here:

https://forum.vcfed.org/index.php?threads/lisa-video-fault.1244688/

Turns out the version of the Apple Lisa Video board had the problematic L3.  The new schematics don't have this one.  I took it out and VOILA Internal Video!!

Here's the original schematic
https://www.dropbox.com/scl/fi/n1riu1172shqnd440vyr2/Orignila-Video-Board.png?rlkey=2tgvg296h2xi2vrguwyooxsy2&st=tqspyyte&dl=0

Here's the one I was working with
https://www.dropbox.com/scl/fi/ppmwnb9ssj04kpvkugbph/VideoBoard.gif?rlkey=638mnegfwaxsft6pylc5af656&st=33kgl8wj&dl=0

and YouTube video to celebrate!!! Crack the champaign.  (errr I still have to deal with the memory errors and install the XProfile), OR proceed to try and get the HDD or FDD running

https://www.youtube.com/shorts/ozIkK0EcnUc
https://www.dropbox.com/scl/fi/d4xqg2zsrw6n0kidnlb5f/IMG_3940.jpeg?rlkey=3di3hpn2xt0otry65k4v61y68&st=it9kjubn&dl=0
https://www.dropbox.com/scl/fi/lnjauvyr0wrvkq9d4yamr/IMG_3938.jpeg?rlkey=tx8b9z8ruq1fv56r6bej52z9c&st=779avtgb&dl=0

[sigma7]

SUCCESS!!!!!

https://forum.vcfed.org/index.php?threads/lisa-video-fault.1244688/

Congrats! That's an interesting thread at vcfed.

The final version (as far as we know) of the Lisa Video Board Schematic is Rev J:

[ried]

Congratulations! That's a major step.

[stepleton]

Congrats! Is there a way to check whether L3 has failed somehow? I'm not sure what to measure without slightly unusual equipment; it's an inductor, so you would expect a continuity measurement to be a dead short even with the part in working order.

[sigma7]

Is there a way to check whether L3 has failed somehow?

L3 can just be deleted from the Lisa Video Board as a non-critical (or inconsequential) part, so that's a simple way to determine if it is causing a problem.

However I suspect your question is less about fixing video boards and more about troubleshooting techniques...

I'd also like to know the technique if something other than an open circuit failure can be figured out with simple equipment. Not having a good answer to how this could be done, some speculative brainstorming:

I presume the inductance value will be a bit low, but perhaps not by enough to distinguish it from a good part with an inexpensive LCR meter.

There is a scope trace in the vcfed thread and an expert analysis response that indicates the energy storage is suspect, but I expect other parts in the circuit could cause a very similar symptom.

I have used an LCR meter that reports inductor "rings" - measured from decaying oscillations when its stimulus is stopped. I expect it is reliable when comparing good and bad parts, but it seems to be a somewhat arbitrary measurement if you don't have a good part to compare.

There are low cost vector analyzer products that I'm guessing could help, but those are even less commonly useful than an LCR meter.

I wonder if applying a specific DC current and measuring the lifting capability of the resulting electromagnet would be indicative.

For most measurements, it seems a good part to compare seems necessary, or at least a published reference. Is there any point in my measuring a good L3 for future reference?

[stepleton]

Is there any point in my measuring a good L3 for future reference?

I suppose there isn't a pressing one, and perhaps it's mainly my curiosity. We know L3 is bad, but since deleting it is fine, that means that it can't have failed open. I suppose coils could have shorted? I'm wondering what could have gone wrong. Perhaps knowing would be useful somehow, or at least interesting.