hmm, using Roman555 provided diagram as a reference trace one of the RGB signals all the way to the chip and measure resistance to ground at each point of the filter
Im running out of ideas, its getting its supply, DAC reference is internal, what else could influence all 3 analog channels? bad blanking? check with another monitor? slap an oscilloscope on the output signals(rgb and VH syncs)?

Well, I have no technical education and I am not good at reading schematics (also I cannot identify a filter).
I tried tapping a board several times, tried another monitor, no changes.
I notice that dim pictures on the screen is a bit distorted like pixel clock and phase are set incorrectly.
Maybe it's up to Via chip then? Applying pressure on the chip makes no difference, so probably not a bad contact.

You can try some coolant spray and "deepfreeze" the chip (then heat it up) to see if this has an effect on brightness.

I treated the chip with heat gun (set to 100 degrees Celsius), no effect.

I guess a broken capacitor (reference designator C2) can make such defect. Try to find it. I image this is a little smd component. Maybe it's damage or missing at all.
P.S. My wild guess of its position on the mainboard. Of course it's necessary to measure and understand precisely.

smoke86 wrote on 2022-10-20, 19:43:

Well, I have no technical education and I am not good at reading schematics (also I cannot identify a filter).

you are doing great

smoke86 wrote on 2022-10-20, 19:43:

tried another monitor, no changes.
I notice that dim pictures on the screen is a bit distorted like pixel clock and phase are set incorrectly.

are you testing with lcd or CRT monitors? can you make a picture? there is potential for V or H sync being broken

The biggest SMD rectangles on the side of VIA chip all in a row starting with L44 L45 L46 and ending on the other side with L47 L48 L49 L50 L52. Additionally there is another block of inductors next to VGA socket. I am assuming those are where RGB V H SDA SCL are routed.
-Measure all of those inductors resistances to ground, we are looking for low readings, an outlier
-map them to VGA pins

rasz_pl wrote on 2022-10-20, 21:53:

are you testing with lcd or CRT monitors? can you make a picture? there is potential for V or H sync being broken […]
Show full quote

are you testing with lcd or CRT monitors? can you make a picture? there is potential for V or H sync being broken

The biggest SMD rectangles on the side of VIA chip all in a row starting with L44 L45 L46 and ending on the other side with L47 L48 L49 L50 L52. Additionally there is another block of inductors next to VGA socket. I am assuming those are where RGB V H SDA SCL are routed.
-Measure all of those inductors resistances to ground, we are looking for low readings, an outlier
-map them to VGA pins

I tested both CRT and LCD.
Regarding inductors, I understand that its resistance should be fairly low, but not direct short, so faulty one will be either high or short.

rasz_pl wrote on 2022-10-20, 19:27:

hmm, using Roman555 provided diagram as a reference trace one of the RGB signals all the way to the chip and measure resistance to ground at each point of the filter
Im running out of ideas, its getting its supply, DAC reference is internal, what else could influence all 3 analog channels? bad blanking? check with another monitor? slap an oscilloscope on the output signals(rgb and VH syncs)?

Also I agree with rasz_pl too. It's better to measure the RGB Hsync Vsync signals of VGA connector relatively to the GND rail in DIODE mode of a multimeter (red pin to GND). Of course the system should be completely POWER-OFF and monitor is disconnected!

P.S. It's correct, but a good inductor can have very low resistance. So it's about of "either the high resistance"

smoke86 wrote on 2022-10-21, 06:44:

Regarding inductors, I understand that its resistance should be fairly low, but not direct short, so faulty one will be either high or short.

smoke86 wrote on 2022-10-21, 06:44:

Regarding inductors, I understand that its resistance should be fairly low, but not direct short, so faulty one will be either high or short.

1 shove one of the multimeter probes into a screw hole at the VGA or LPT connector, set multimeter to resistance or diode, buzz all of the inductors around looking for abnormal low readings
2 diode mode, shove a wire/long resistor leg into VGA connector (we are interested in pins 1 2 3 13 14 Re: IBM 8503 Monochrome VGA Monitor Help), make a loop at the end and squeeze multimeter probe into it so its firmly there, buzz all the inductors with the other one until you find ones that beep (and make sure they beep on both sides of inductor), write/map them down

Is it possible that more than one inductors beep (on both sides) on certain pins of vga slot? I am doing it on area of L23, L22 and above.
I also found suspiciously low impendance (0,4 ohm) on L22. Others are >35ohm or over 2k ohm.

2 KOhm?
I would suspect something fishy here.

Btw you´re probably not measuring impedance but rather DC-resistance.

Oh, there goes my lack of knowledge. You are right.
I checked those in diode mode and one of them showed very low reading.

2Kohm to ground is fine
0,4 ohm to ground might be problematic depending on what that L22 is used for - thats why I asked you to map them to VGA pins

>Is it possible that more than one inductors beep (on both sides) on certain pins of vga slot?

yes

1/ plop multimeter to pin 1 of VGA connector
2/ go around all the inductors finding the ones that are connected, mark it down in mspaint or something
3/ go to 1/, but with pin 2, then 3 13 14

with that map we will know which pins are important for VGA. L22 L23 look like they are for LPT, but you never know without measuring

>Others are >35ohm or over 2k ohm.

well, this is bad. I mean this is good 😀 as in no shorts. So we are left with possibility of V or H path being broken maaaaybe. take a picture of the faded desynchronized screen you described

Well, the result is weird.
I numbered insulators 1 to 8 as on photo attached.
So VGA pins beeps as following (on both sides):
Pin 1 - 3, 5, 8
Pin 2 - 3, 5 ,8
Pin 3 - 6
Pins 13 and 14 - nothing anywhere (I actually tried to check with mulitiple components in vicinity, no match), althouth multimeter, when set to continuity mode, shows some readings (mainly 535, 630 and over 2k)

So my first guess were broken traces/bad VGA connector.
I saw someone tinkered with vga connector before me and I resoldered it, but it did not change anything.
I checked continuity from connector to solder joints on the other side of board and it is ok.
So at this point I guess I will need to remove VGA connector and check traces.

Edit: I also attached a photo of what Windows 98 loading screen looks like. It is only visible at certain angle, my camera cannot see the image if I try to take a photo frontally.

smoke86 wrote on 2022-10-22, 18:04:

Pin 1 - 3, 5, 8
Pin 2 - 3, 5 ,8

that would mean pin 1 and 2 of VGA connector are shorted? Did you perhaps mix pins 1 2 for 5 and 4? looking at male pinout while connector on the board is female thus reversed?

smoke86 wrote on 2022-10-22, 18:04:

Pins 13 and 14 - nothing anywhere (I actually tried to check with mulitiple components in vicinity, no match), althouth multimeter, when set to continuity mode, shows some readings (mainly 535, 630 and over 2k)

do the "L44 L45 L46 and ending on the other side with L47 L48 L49 L50 L52" inductors too after making sure you got VGA pins right

smoke86 wrote on 2022-10-22, 18:04:

Edit: I also attached a photo of what Windows 98 loading screen looks like. It is only visible at certain angle, my camera cannot see the image if I try to take a photo frontally.

I dont see problems with geometry

The image is there, so I guess there's no problem with H and Vsync.

You mentioned inductors having high resistance of up to 2kohms when measuring across them, on resistance mode? They're definitely broken, normal DC resistance for those should be around 0.5ohm. I had a motherboard that had a bunch of those failed, resulting in non-functional PS2 ports (both mouse and KB) as well as non-functional USB on the back panel. Visually they were OK, but when desoldering them half of the inductor stuck to the soldering tip 😁

I'm curious about the advice to use red probe to GND, as I always do the opposite when probing things on a board. Is this specific to VGA output circuitry, or should it be used no matter what? My reasoning for using black to GND is not to inject negative voltages where they aren't usually present, but I might as well be very wrong.

Inductor 6 (L21) looks broken.
Can you verify ?

#3, 5 and 6 seem to be in the colour channels (75R resistors) so when there´s an interruption in #6 only one colour would be affected.

quicknick wrote on 2022-10-23, 09:09:

I'm curious about the advice to use red probe to GND, as I always do the opposite when probing things on a board. Is this specific to VGA output circuitry, or should it be used no matter what? My reasoning for using black to GND is not to inject negative voltages where they aren't usually present, but I might as well be very wrong.

I saw this recommendation on ASUS repair guides. It also provides there a reference data to compare.
I think it doesn't matter how exactly you measure but obviously you have to do all measurement uniformly

@rasz_pl
Yes, pins 1 and 2 are indeed shorted (I know there shouldn't be a short there). I did not confuse pins, the short is also present on the solder joints of VGA connector.

I don't understand what you ment by "do the "L44 L45 L46 and ending on the other side with L47 L48 L49 L50 L52", shall I check continuity with pin 13 and 14 with those inductors?
I checked it, but no continuity to pins 13 and 14.

You can't see a problem with geometry, because picture is little wavy and it is not possible to capture it with camera, especially on static photo.

I did as you said about measuring these inductors in diode mode - I found that L22 reads .000 at one side and .035 on other side (unlike other ones, that gives sensible reading on both sides).

@SDumas
Inductor L21 is fine, it is just some dirt on it.