way odd color problem

[Arakon]

I got a 4 slot here which has a really odd color problem.

the green color is missing some shades.. namely the brighter ones. instead, the shades "start over" at dark green.

the red line is just there to show where it starts over.

which also results in white being normal in the gray shades, but once it gets to brighter gray and white, it turns purple cause green is darker than supposed to be.

this is NOT a supergun wiring problem, mind you.. I tried with two, both work flawless on other boards.

any idea where to look and possibly replace?

 

[ttooddddyy]

The RGB outputs are derived from simple digital to analog resistor ladder arrays doubling in value up the ladder. These are a series of individual resistors located near the jamma/mvs edge connect (some boards may have discrete flat pack arrays, not familiar with the 4 slot boards) My guess is one of these resistors has gone high resistance on the green DAC resistor array. The values may differ slightly, but the diagram gives the general idea, there will be seven resistors for each of the RGB outputs.

 

[MKL]

On 4-slots (and the majority of other mobos) there's an array of 21 resistors, 7 for each colour. Check the green ones. If the LS273's (the flip-flop before the resistors) were bad I think you'd have more serious problems.

 

[Arakon]

I checked the resistors, and the green 3.9 kohm one reads 4.2 kohm.. HOWEVER swapping it with another 3.9 kohm resistor made no diff at all.. here's the odd part:

replacing the green 220 ohm resistor with a 100 ohm one made the green almost right, just a slight touch too dark.. so a 80-85 ohm resistor would correct the color to the proper value. I'd like to do a "proper" fix, tho.. are you sure it's not the 74ls243? if it is one of them, would the 74HC243 also work? I believe it needs higher input voltages to trigger than the LS one.

 

[ttooddddyy]

Different manfacturers

http://www.onsemi.com/pub/Collateral/SN74LS273-D.PDF
http://www.datasheetcatalog.com/datasheet/7/74HC273.shtml

From what I understand the LS is for low power and HC high speed applications.
In most cases they would be interchangable.

 

[Razoola]

I'm sorry for your problem and I cant help much fix it but man I am happy the color bars I added to the UNIVERSE BIOS v1.2 have come in useful in helping fault tracking this one

Raz

 

[MKL]

I've checked the resistor values on my 4-slot: I read exactly 3.9k for each one. I got exact values also for all the other resistors. So 4.2k cannot be normal. Check all the resistors. If the problem doesn't go away you could replace the LS273's, better both since the green resistors are connected to both. These ICs are easy to find and inexpensive. Oh and don't forget to socket them.

 

[ShuckNasty]

Word up.

Great thread, this is the type we need more of.

 

[Arakon]

@mkl:

the odd part is just that it made no change at all when I swapped the green and the red 3.9 kohm resistor around, it still looked the very same as before. ( 4.2 on red and 3.9 on green after swap)

 

[apus]

Just curious: What happens if you leave the 3.9k resistor completely out?

 

[Arakon]

nothing. it doesn't seem to change anything.

if I bridge it (basically 0 ohm), the second half (where the colors start over) is entirely bright green.

 

[apus]

Well, then I would definitely agree to change the latch. Maybe swap two of them (yes, soldering sucks, but you can try out today at least ).

 

[ShuckNasty]

I don't really know that much about this, but could it be a cap problem? I figure I'd just throw that out there anyway.

 

[Arakon]

no caps involved there.

@apus:

I have a pretty clean way of doing it (clean for the pcb, not the rest).. I just use a dremel with cutoff wheels to cut the pins off the chip, then heat up each pin and pull it out with pliers.. that way there's no risk of ripping traces off cause a hole wasn't fully cleared.

 

[ttooddddyy]

I would check the continuity between the G array and the flip flop ICs. Also compare the resistance of the G array at each step up the ladder compared to the R and B.

With the circuitry being close to the jamma/mvs edge connect, perhaps in the past a ham fisted board jockey has managed to crack the pcb around that area.

 

[Arakon]

does anyone have a diagram of which resistor is supposed to go to which pin? they change layers several time on the way to the chips, it's a bitch to trace back.

resistance was checked, same for all except for that one 3.9 kohm resistor, which didn't change anything after switching with a good one.. not to mention that it doesn't even make a difference if it's left out completely.

 

[ttooddddyy]

does anyone have a diagram of which resistor is supposed to go to which pin? they change layers several time on the way to the chips, it's a bitch to trace back.

resistance was checked, same for all except for that one 3.9 kohm resistor, which didn't change anything after switching with a good one.. not to mention that it doesn't even make a difference if it's left out completely.

measure the resistance from ground to each step of the ladder and compare the readings to the R & B arrays. It would be a real bummer trying to tace the tracks on a three layer board.
I will trace them on a two layer board and post a diagram later.

 

[Arakon]

hmm.. all the green ones seem to have a higher resistance to ground than the red and blue ones. the odd part is that the first half of the shades are perfectly alright.

edit: the resistors themselves have the right values, tho.

also, with a pot I managed to adjust the green shades to look right now, however the pic still got a slight purple tint, which leads me to believe that ALL greens are a bit too low.

I ordered new flip flops to replace these, I hope that's all it takes.

 

[ttooddddyy]

I sketched a diagram for the RGB DAC circuit on a six slot which is easy as its only a two layered board. Will scan it and put it up tomorrow. It goes like this.

RED (flipflop 1)
150 74LS05 Hex inv 10
220 74LS273 Flip-flop 12
470 6
1K 15
2.2K 5
3.9K 16
8.2K Hex inv 2

GREEN
150 Hex inv 8
220 2 (red)
470 19 (red)
1K 9 (Blue)
2.2K 12 (blue)
3.9K 6 (blue)
8.2K Hex inv 4

BLUE (flipflop 2)
150 Hex inv 6
220 15
470 5
1K 15
2.2K 2
3.9K 19
8.2K Hex inv 12

Hope this helps.

 

[MKL]

I got the same results on the 4-slot 1 ver. but the newer version is (partly) different, the red for instance is:

150......LS05 (8)
220......LS273 (9)
470......LS273 (6)
1k........LS273 (5)
2.2k.....LS273 (2)
3.9k.....LS273 (16)
8.2k.....LS05 (2)

 

[ttooddddyy]

Thanks MKL,I will check that against a 1FS (3 layers) I guess it will be the same as the later version 4 slot.
With a bit of luck there are only two different circuit variations around this area accross the range of boards (2 &3 layers), lets hope SNK kept some uniformity of design.

 

[ttooddddyy]

I got the same results on the 4-slot 1 ver. but the newer version is (partly) different, the red for instance is:

150......LS05 (8)
220......LS273 (9)
470......LS273 (6)
1k........LS273 (5)
2.2k.....LS273 (2)
3.9k.....LS273 (16)
8.2k.....LS05 (2)

The MV1FS and MV1T are different again.

RED.......MV1FS.............MV1T
150......LS05 (2).............(6)
220......LS273 (16)
470......LS273 (15)
1k........LS273 (12)
2.2k.....LS273 (9)
3.9k.....LS273 (6)
8.2k.....LS05 (12)

 

[Arakon]

I decided to just swap the 273's, I desoldered them, replacements will arrive tomorrow hopefully. I checked the traces after removing the chips, they all appear to be in great shape, also did some continuity checks on various traces and they seemed to be good (didn't check every single one).

 

[ttooddddyy]

The 150 and 8.2K connect to the 74LS05, and the others should have two connections to the R flipflop and three to the B flipflop 74LS273s. If one of these ICs was faulty I cant help but think it would have an effect on the R and B outputs as well.

 

[Arakon]

I can't find any other problems (other than that one resistor, which didn't make any difference even after I swapped or even totally removed it).

also, what if just one output was damaged or outputting a weaker signal?