MSXmakers support

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By GFX

Supporter (7)

GFX's picture

22-03-2022, 16:22

Thanks, I'll try with a stronger PS and let you know !

By GFX

Supporter (7)

GFX's picture

23-03-2022, 21:01

I did try with a 6A power supply and with new capacitors, I even put a 330uf at the 5V input and nothing changed.
I still have some noise in the image...

By msxmakers

Champion (454)

msxmakers's picture

01-04-2022, 11:48

Of course it have its origins in many places, but it uses to be the PS.
A good way to find it might be to display the noise on an oscilloscope and follow it from audio output to its internal source. Then you just have to act on that zone (replace a component or socket or re-tin it).
Greetings.

By crisag

Supporter (16)

crisag's picture

02-04-2022, 03:06

GFX, are you using Composite, SVideo, or RGB? Quality increases in that sequence.

By RayneX

Rookie (32)

RayneX's picture

26-05-2022, 07:08

Hello. First time poster. I'm in the middle of building the Omega MSX system. I've been able to complete Smoke Test 1 and 2. Smoke Test 2 had the black screen with a signal, but that is a possible result from that test. I went to Smoke Test 3 with the VRAM install and I do not get a screen. Signal is detected, but nothing is shown. I tried Composite and S-Video.
Jumpers are set to NTSC, VDP is properly set, CMOS Jumper is on JP1 using the Halt Bios, so it should be accessing the C-Bios. Any ideas where I should start hunting down a possible cause? I do not have a scope nor do I know how to use one. I'd appreciate any help.

By msxmakers

Champion (454)

msxmakers's picture

26-05-2022, 10:17

RayneX wrote:

Hello. First time poster. I'm in the middle of building the Omega MSX system. I've been able to complete Smoke Test 1 and 2. Smoke Test 2 had the black screen with a signal, but that is a possible result from that test. I went to Smoke Test 3 with the VRAM install and I do not get a screen. Signal is detected, but nothing is shown. I tried Composite and S-Video.
Jumpers are set to NTSC, VDP is properly set, CMOS Jumper is on JP1 using the Halt Bios, so it should be accessing the C-Bios. Any ideas where I should start hunting down a possible cause? I do not have a scope nor do I know how to use one. I'd appreciate any help.

Hi RayneX,
Even if you have an AM29F040 it should work just the same.
It's not likely to be a problem with the VRAM because they would have to be 2 bad, the only one that matters at power up is the lower pair, if U8 or U9 is good you should see a buggy screen but not just black.
Normally test 2 does not show a black screen all the time, but the screen with only one color, it can be black but it is not likely that every time you turn it off and on it will be black, although it is possible when there are NTSC / PAL problems, in that case everything is black and white and you might get a gray screen.
Is it a pity that you don't have an oscilloscope or do you say you don't know how to use it?
It's basically a tool to see an alternating signal, you can see its frequency and its amplitude. Having one now would help you know if the CXA1645 shows the same thing on its input and output, eg pin 2 is the R (red) input and pin 23 is the output. The output may be amplified but what is certain is that if there is a signal at the input and not at the output, the chip will be bad.
You could try the same thing for pin 3 and 22, pin 4 and 21, and pin 10 with 20. They are not exactly the same signal, but you need to check that at 23, 22, 21 and 20, there is something else. what a noise.
In any case, it is very likely that the problem will not be the CXA1645 chip, because this problem that you mention is very common and usually occurs with any other chip that is in smoking test 2, if any of them does not work.
The most common case is that a weld is poorly done or a socket is not working properly.
Check all the chips because some may have a bent pin underneath and you might think that everything is connected correctly, if everything is ok, check all the solders involved, they have to be shiny and smooth. Make sure they are all good using flux and then clean the welds well to inspect them with a magnifying glass.
To rule out that it is a bad socket, you can only test continuity, pin to pin, with the multimeter, measuring between the top of the pin and the bottom solder loosely.
If you have a multimeter with frequency measurement or you can buy a cheap frequency meter kit, you can do the checks at the end of my article:
https://msxmakers.design.blog/proyectos/omega-home-computer/omega-paso-a-paso/
"I HAVE A PROBLEM WHAT TO DO!"
And
"I HAVE NO VIDEO SIGNAL!!!"
They are tests that also appear mostly in:
https://github.com/skiselev/omega/blob/master/Mainboard_Building_Instructions.md
Although on my page you have photographs of what the oscilloscope could show as a help.
For some reason, it is more common for a problem of this type (socket or solder) to occur on GAL chips so check these first, check that they are in the correct order and that they have the correct program. And then check the soldering or continuity on its pins first than the rest.

By RayneX

Rookie (32)

RayneX's picture

27-05-2022, 02:46

Thanks for the tips. I reflowed all the sockets related to those that are occupied and swapped some components that I had extras of and reseated every chip. That didn't work, so I'm now leaning towards the GALs and Flash ROM being corrupted during programming. I'm going to try to program them myself tomorrow. Hopefully I can get the software up and running correctly.

By RayneX

Rookie (32)

RayneX's picture

27-05-2022, 06:34

Alright, I read through your Mainboard Building instructions to see if I could use my multimeter to get the frequencies to match from the list. I am not getting a match on the ones I was able to test. I couldn't test the ones looking for pulses.
The variances I'm getting are the following:
VDP (U3) - CSYNC - Pin 6 - 16.23KHz.
CXA IC (U47) - SYNCIN (Pin 10) and SCIN (Pin 6) - I'm getting nothing on my multimeter. I checked the traces and pin continuity, and they all lead to their respective places.
CLK signal on U3 and U1 are usually 3.578MHz. I think that's good enough for the multimeter, although I see it go into the 4MHz range for U3 (VDP) every once in a while.
Does this lead anyone to a specific possibility on what's wrong?

By msxmakers

Champion (454)

msxmakers's picture

27-05-2022, 09:26

RayneX wrote:

Alright, I read through your Mainboard Building instructions to see if I could use my multimeter to get the frequencies to match from the list. I am not getting a match on the ones I was able to test. I couldn't test the ones looking for pulses.
The variances I'm getting are the following:
VDP (U3) - CSYNC - Pin 6 - 16.23KHz.
CXA IC (U47) - SYNCIN (Pin 10) and SCIN (Pin 6) - I'm getting nothing on my multimeter. I checked the traces and pin continuity, and they all lead to their respective places.
CLK signal on U3 and U1 are usually 3.578MHz. I think that's good enough for the multimeter, although I see it go into the 4MHz range for U3 (VDP) every once in a while.
Does this lead anyone to a specific possibility on what's wrong?

If I understand you correctly, you say that CSYNC has a 16Khz signal on pin 6 of the VDP but pin 10 of the cxa... has nothing?
follow the diagram and you will see which elements are involved JP4 has to be at 2-3 and you have to find where the signal is lost, therefore measure the frequency at pin6 of U3, then at R27, before and after, then at JP4 , then on the solder of U47 (pin 10), on its socket, on its pin... somewhere the signal must be lost.
Or do you have an intermittent problem that varies by pushing the chips on the board...
Once you have followed this path with CSYNC, do the same with SCIN, looking at the schematic.

By RayneX

Rookie (32)

RayneX's picture

28-05-2022, 07:19

Quote:

If I understand you correctly, you say that CSYNC has a 16Khz signal on pin 6 of the VDP but pin 10 of the cxa... has nothing?
follow the diagram and you will see which elements are involved JP4 has to be at 2-3 and you have to find where the signal is lost, therefore measure the frequency at pin6 of U3, then at R27, before and after, then at JP4 , then on the solder of U47 (pin 10), on its socket, on its pin... somewhere the signal must be lost.
Or do you have an intermittent problem that varies by pushing the chips on the board...
Once you have followed this path with CSYNC, do the same with SCIN, looking at the schematic.

I followed the schematic with a help of a friend. We're starting on Pin 6 of the VDP getting 16.23khz signal. I get the same signal on one side of R27. R27 shows a resistance of 1k, which is correct, but I get 0 frequency on the other side of the resistor. I'm not understanding how that's possible. I also checked C85 and also get 0 frequency on both sides of the capacitor. Capacitor is tested to be .1nF, so that's probably good. I don't have a sensitive enough Multimeters to get it down to pF. All continuity of the circuit are good as well. Not sure what we're missing here. Something is blocking the signal at that R27 resistor.

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