ScuzzBlog: Diaries May 2020

Entry 16th May 2020: Post 1: Amiga 1200 fault - Green tint to screen.

Amiga 1200 fault - Green tint to screen.

I got so annoyed with the green tint to the grey on this one A1200
that I decided to pull the hard drive from her and  stick in another
of my 1200s. The screen has a faint green tint to the grey on the screen.

The fault can be traced to the VIDEO-DAC chip VP101-3BA. There are
six resistors associated with the DAC and Lisa that are of either
25 or 50 Ohms and it's worth checking those also. But most likely
the VIDEO-DAC is at fault and needs replacing.

You can buy these quite cheap from China even today on Ebay.

To check the fault if you load up Pro-Tracker and go into the set-up
you can use the RGB sliders to check the intensity of colours. With
a green tint or failure of the blue, often there will be no change
in intensity of the colour for half the bar. Then the colour grading
will ramp up from only one half of the bar. The Red and Green kick
in almost immediately you start the slider.

Problems with the resistors generally cause a colour issue on the
boot screen with the wrong colours displaying. A green tint on the
grey Workbench screen points to the actual VIDEO-DAC. Fortunately I
have a few replacements on old boards if I wanted to use them

While I had the 1200 out I checked over all the capacitors. I
rarely get troubled by capacitors. Haven't recapped any of my 1200s.

So look out for VIDEO DAC BT101 or VP101 or something with 101. Just
above the LISA top left. Or you could do what I did, and just call
the poor thing 'BiaGreenie' and put up with it.... or not. 


Watch the sliders in ProTracker

Amiga 1200 fault - Green tint to screen.

The ProTracker software used.

Screen with the grey tinted green.

The ProTracker screen should be light blue.

Use the slides to show the colour intensity.

Comparing screens of faulty and good.

Replacement on other motherboard.

VIDEO-DAC schematic.

Ebay prices for the VIDEO-DAC

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Last updated 16th May 2020

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