Apple Lisa vertical collapse

[d3jsp]

Hey all, does anyone know which part of the Lisa video board is responsible for vertical deflection?

It worked in the seller's pictures but complete collapse when I turned it on. Probably broken solder joints right? Or which capacitor should be replaced first

 

[d3jsp]

It also has a mod on the height potentiometer toggling between 151k ohm and 76k ohm

 

[d3jsp]

C19 measures in range in circuit, but hard to tell without completely removing it

 

[d3jsp]

I have 28V on the board but seems like it isn't getting to U2 some how. It's measuring 0.7 - 2.4V. Only 3.2V at C12

 

[d3jsp]

Looks like maybe a bad R24. Voltage drops from 31V to 3.5V.
It measures at 150 ohms but should be ~120 ohms according the schematics. Would it cause that much voltage drop across both sides of the resistor?

 

[stepleton]

There is much the Lisa video board has in common with the video system in classic Macs. You might refer to the Dead Mac Scrolls for some troubleshooting hints. See e.g. pages 49 on in this PDF:

https://vintageapple.org/macbooks/pdf/The_Dead_Mac_Scrolls_1992.pdf

 

[d3jsp]

Does anyone know the correct voltages for each pin on U2 TDA1170N?

 

[bibilit]

Have a look at my own post for the Apple II monitor repair, probably related (the monitor is using the same TDA1170)

Here enclosed the SAMS manual, maybe the Lisa is close enough…

 

[d3jsp]

Thank you! That helps a lot. Mine is way off.

Does anyone know the correct resistance for the "width" pot on the video board? Mine says 200 ohms but measures around ~270 already around the mid point.

And how to get replacements that fit?