ReAmiga 1200 build CIA problem

[Castellen]

Image looks too dark on DiagRomRGBBarsTest.jpg?

Yes, compare the colour gradient with the attached photos from my 1084S test monitor, which shows the normal/expected brightness of the pattern.

[Castellen]

Here's the other photo showing the DiagROM test pattern (was over the attachment size limit), ignore the minor glitches in the vertical bars, my test A500 isn't perfect.  The point is that this is the expected image intensity, which is better shown in the gradient bars in my previous post.
 

[imqqmi]

Hi Castellen,

Thanks for the images, good reference! I've received the CIAs and replaced the suspected one and it's all good now!

I've done some testing on the dark image. The pot on R217 didn't help and the oscilloscope plot showed good white voltages of about 1V, but bad black levels, hence the darker tones are too dark. I'll restore the 470 ohm resistor, seems to be a value that's fine. I could get the brighter values more bright but the black level didn't come up.
At some point discovered that I have 74LS166 on U23 instead of 74F139. The latter wasn't on the BOM either. It's a wonder it gives a picture at all. When I hooked up the oscilloscope to pin 12 of U23 probably because of the 50Hz EMI around my workbench it's giving a much brighter but distorted image. Replacing it with the proper IC should solve this issue. Hopefully a 74HCT139 will work as the F version seems to be obsolete. It's about 10x slower (3-4ns vs 40-50ns) but for 50Hz/15KHz sync signals this should be fine.

Man what a stupid mistake, I should've realized sooner. Sorry for the inconvenience and thank you for your patient troubleshooting, much appreciated!

[imqqmi]

I've received the U23 74HCT139 and put it in, and the picture is now perfect! I've finished the build and am an Amiga 1200 owner once more!