Lisa display problem

[Ildefonso]

Hi.

It’s the first time I take part in the forum. I’ve been collecting vintage macs during the last two years and, finally, I’ve been so fortunate to put my hands on one Lisa 2/10. I bought it 4 months ago, and it was perfectly working, but now the display has stop working.

When I turn the Lisa on it makes a scaring sound and the image is totally distorted.

I thought it could be a broken flyback and changed it but nothing changed.

Could any one of you, more expert then me, give me any advice where could I begin to try to fix it?

In general, the Lisa looks like new, even the video card looks pretty new.

Thanks in advance.

(I’ve uploaded a video so that you can have a better idea what I’m talking about)

View attachment 4C29BBB2-D884-4D66-8E7E-2D2692B95AD2.MOV

 

[MOS8_030]

Howdy!

It's likely that your Lisa has some failed/weak capacitors or other components in the power supply and/or the display card.

Check out the information here to start.

http://lisafaq.sunder.net/

 

[Ildefonso]

Hi MOS8_030.

Thanks for your quick answer.

I’ve carefully inspect both power supply and display card and the capacitors look pretty fine. Everything looks pristine new. Anyway, I’ll check them, but I fear the problem is’nt capacitors related.

 

[gilles]

I add exactly the same symptoms with bad capacitors in the power supply last year. They were still perfect visually (I still have them somewhere)

 

[Ildefonso]

As you says, Gilles, perfectly looking capacitors can be faulty. I’ll give it a try since replacing the capacitors will not be harmful at all. I’ll keep you informed of my progress...

 

[apm]

It looks like the horizontal drive is switching on and off. That would be why you see the bright squiggly line, which would be the horizontal sweep collapsing (same thing the Lisa does sometimes when powered down, I think). It's also why you hear the noise. The flyback is also powering up and down with the horizontal sweep.

Possible culprits:

1. HSYNC signal starts and stops (digital / logic board problem)

2. Problem in horizontal sweep circuit, somewhere between HSYNC input and the flyback (video board problem)

3. Power supply problem, especially +12V or +33V lines.

The effect appears pretty regular, maybe 100Hz or 120Hz (i.e. mains line rate). That might suggest something to do with the power supply if one of the filter caps has failed. If you've got a scope, check whether the +12V and +33V lines are steady or whether they're fluctuating. Or just replace all those big caps and hope for the best.

 

[Ildefonso]

Thanks for the replay, apm. Any advice is of great help because I’m very lost with this Lisa systems. I’ve ordered all the caps for both power supply and video card and will keep the fingers crossed

 

[Ildefonso]

Hi guys.

Problem solved thanks your advices. My Lisa is once again up and running...

The culprit, one of the two 470mF/250V capacitors from the power supply that was shorted...



But the second time I turned on the Lisa I got the following error

which I solved simply reinserting the motherboard. Anyway I fear what’s the real problem I got. 

Any idea?

View attachment file