Different CPC models and image quality differences?

[CFox]

I bumped into a neat and quite early 6128 a while ago and couldn't resist getting it although I already have one little bit later model. Couple of days ago I started to fiddle with it more after I cleaned it inside out and replaced floppy drive cable. This new older... newer older... FFS, the earlier system I got is manufactured in early 1986 and is CRTC0 system with blank badge and the later model is from 1987, CRTC1 and striped badge. This older unit has MC0020B motherboard, but I can't for the life remember the later model as I haven't opened and checked it in years.

Now, immediately when I started to use this earlier unit with CTM644 (and also CM8833mk2, same applies), I immediately thought that this earlier system has better image quality and in my opinion newer system has somewhat softer image. Difference isn't earth shattering, and something that would point to a actual fault in the later unit, but it is still noticeable. I haven't tested them side by side as it is practically impossible, but right after each other and I could swear I'm not imagining all this.

These kind of differences aren't uncommon in this era, for example earlier C64 models have much worse image quality compared to later ones. I have C64s with 250407, 250425 and 250466 motherboards, and 407s are much worse and even getting them roughly on the level of the latter two requires both lumafix and tuner replacement. Both 425 and 466 are good and equal, because the board layout is more or less the same on those, except memory. Back in the day most people used RF with C64s, so these differences weren't noticeable, but nowadays with quality CRTs and yC cables IQ differences are very clear.

All this is well known in the C64 community, but I don't remember seeing much discussion about this with CPCs. So, my question for those of you who have multiple systems, perhaps having bunch of 464s, 664s, 6128s and plus models, have you at any point noticed IQ differences between different revisions?

[McArti0]

https://www.cpcwiki.eu/index.php/Mainboard_Versions

search your later model...

[CFox]

https://www.cpcwiki.eu/index.php/Mainboard_Versions

search your later model...

It most likely is different and at least CRTC is different, but my main point was just to discuss if people generally have noticed IQ differences between different revisions or even different CRTC versions.

[McArti0]

Differences in the color image may result only from the GA bandwidth and the length of the RGB path and values c139,140,141, r125-130.
You need to open the old cpc...

[abalore]

It's not likely the image differences come from the digital part of the board, take a look to the components in the analog part for RGB, comparing values, voltages, etc.

[abalore]

I would specifically review the capacitors since you are talking about differences in softness. It may be related.

[CFox]

I would specifically review the capacitors since you are talking about differences in softness. It may be related.

Yeah, I check the newer model I already had before, check the MB revision and compare the actual layout and components more thoroughly when I have time. I don't find it likely that CRTC for example makes any difference either. It is also possible that the softness is due to interference and noise introduced by the motherboard layout itself, that is signal traces affecting each other and introducing noise. In those days PCBs were poorly if at all optimized for interference. Of course due to low clocks it wasn't that important as it is nowadays, but they still have an effect.

I find this interesting observation generally and as I said, I haven't seen possible differences between the plethora of MB revisions discussed before in this regard.

[ZorrO]

As I know, LC and PLUS models have RGB equal resistors 50% each color in gray, but older models have a different resistor in green one - it gives 60%, and red and blue - 50%. What changes few colors, most visible change in color 12, which looks like dark yellow in LC and like olive green in older CPC.