[LisaFAQ] > [Hardware] > [Video and CRT]

3.16.4. My Lisa's display is wavy, wobbly, or shows worms/ripples. How can I fix it?

An unstable display can be caused by lots of things. Uncommon problems include a strong source of interference from an electromagnetic source nearby. More common problems include dirty potentiometers on the video board, oxidized contacts on the power supply, CPU, or I/O board, and high load on the power supply caused by one of the devices inside the Lisa.

If the display is unstable, first see the section on cleaning/adjusting the potentiometers on the video board.

If the display is stable, but the image is wavy, these are some additional causes:

A1 Reseat the Power Supply and clean the connector

Simon Claessen has reported that cleaning the Power Supply contacts with a pencil eraser, and reseating it solved this problem. You might want to attempt to do this first.

Be gentle when cleaning the contacts, be careful not to damage the contacts. Better yet, use an electronics contact cleaner.

James MacPhail recommended "Clean with alcohol or electronic contact cleaner. (The latter often includes a silicone lubricant which is likely to preserve the life of the contacts by reducing friction and oxidation.)"

A2 Check for PSU overload

If your Lisa has an internal hard disk or other added load, try disconnecting it to see if the display becomes stable. If so, consider these possible solutions:

A3 Check/Replace video board

Some wavy video problems are caused by a bad video board. Check the capacitors, voltage regulator U1, and for burned resistors.

A4 Horizontal Phase modification

If you are using the 1.2 Amp Apple PSU, try moving the HOR PHASE control on the video board to the extreme left. If this solves the ripple problem (but causes the video to fold over on the left), you can try the following modification. 

In this case, it is best to upgrade to the 1.8 Amp DataPower PSU if possible

WORKING AROUND THE VIDEO CIRCUITRY OF THE X/LISA WILL EXPOSE YOU TO POTENTIALLY LETHAL COMPONENTS. PERFORM THIS WORK AT YOUR OWN RISK

Some X/Lisas display wavering / wandering pixels which is sometimes aggravated by increasing the load on the power supply via memory boards or other additions.

The problem is due to poor filtering in the power supply, which couples the ripple on the 5 volt supply into the 33V supply for the video circuit board.

The problem seems to vary from machine to machine. It is aggravated by dirty contacts on the card edge connectors associated with the power supply, motherboard power and video circuit boards.

The ripple enters the video circuit via the Horizontal Phase control on the video board. The effect of the ripple is minimised by rotating the Horizontal Phase control to the counter-clockwise extreme. If this removes the problem entirely, then the following alternative method of adjusting the horizontal phase of the image may be used to prevent re-introducing the ripple into the video circuit.

Note that video circuits incorporate high voltage charge storage components that can deliver fatal electric shocks even after the computer has been unplugged for some time. Do not work on the video circuitry unless you are familiar with high voltage work.

Note that the neck of the display tube is fragile and easily broken. Because the tube contains a vacuum, there is danger of flying glass should the tube be fractured. Suitable caution and protective goggles are required.

When the Horizontal Phase control is adjusted to the CCW extreme, the image on the screen usually wraps around the edge of the CRT. With the phase control adjusted to the extreme, the addition of a capacitor between the base of Q8 and ground will move the image back towards the center of the screen. (The left side of R54 is equivalent to the base of Q8. The bottom of C5 and the emitter of Q8 are ground.) The amount of capacitance required will depend on the particular machine. 0.02uF (0.02 micro-Farads) is a good starting point. The capacitor should be rated at 50V or more. Ordinary ceramic capacitors are more than adequate.

Suggestions:

Turn off the machine, unplug it, and leave it overnight, longer if possible.

Instruct someone nearby that they may need to give assistance in case of an accident

Treat the CRT neck with great care to prevent breakage and flying glass. Be careful to avoid pulling on the wires that go to the CRT. Stay clear of the red high voltage wire attached to the stinger in the top of the tube to prevent electrocution.

Remove the top cover of the X/Lisa.

WORKING AROUND THE VIDEO CIRCUITRY OF THE X/LISA WILL EXPOSE YOU TO POTENTIALLY LETHAL COMPONENTS. PERFORM THIS WORK AT YOUR OWN RISK

Remove the video board: There are a few connectors that will have to be disconnected from the board. Be careful not to yank the wires as you disconnect them. You will have to unplug the multi-wire cable from the neck of the CRT to move the video board more than an inch or two. There are two phillips screws near the top of the board. The bottom of the board goes into a card-edge connector.

Check the location of the capacitor to be added and install some socket pins or flying leads so that the size of the cap can be changed without additional disassembly.

If you have some confidence and another video board to inspect, you may be able to solder the cap on without removing the video board from the machine. You should still allow as much time as possible for the CRT to discharge with the machine unplugged.

Install the capacitor, re-assemble the machine, and try it out. The Horiz. Phase control should be at the CCW extreme. If the image moved too far, use a smaller capacitor. If you want the image moved over further, use a larger capacitor or adjust the phase control.

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