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Forum Index : Microcontroller and PC projects : CM2: No RED, just blue, green, and black showing

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bar1010
Senior Member

Joined: 10/08/2020
Location: United States
Posts: 197
Posted: 02:36am 30 Aug 2020
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I have not been able to see the RED part of the RGB for VGA connection.  Am just seeing variations of blue and green colors with a black background.  This is the case when connected to a Samsung 50 inch Plasma tv and also when connected to an ASUS VN279 monitor.
Has anyone had this or a similar issue?
 
TassyJim

Guru

Joined: 07/08/2011
Location: Australia
Posts: 6283
Posted: 03:30am 30 Aug 2020
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Most likely point of failure is

Your cable
Socket where it's soldered onto the board.
Shorted 75 ohm resistor
Short or open circuit trace from socket to resistor networks.

The pins on the CPU are not likely because there are 5 and failure of all is not plausible.




Jim
VK7JH
MMedit
 
darthvader
Regular Member

Joined: 31/01/2020
Location: France
Posts: 87
Posted: 12:01pm 30 Aug 2020
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Hi ,
I think it's really not possible to not solder ALL resistors from the Red R2R DAC part.
So i recommend you to check the soldering point on the pin 1 from your VGA connector.
Edited 2020-08-30 22:03 by darthvader
Theory is when we know everything but nothing work ...
Practice is when everything work but no one know why ;)
 
bigmik

Guru

Joined: 20/06/2011
Location: Australia
Posts: 2950
Posted: 01:29pm 30 Aug 2020
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Hi Bar1010, All,

If you think your cable and monitor are ok, tested on another device, I can see only 2 possibilities.

As mentioned check pin 1 on the vga connector for damage (looking into the socket) or bad soldering.

The only other thing I can see is an incorrect value of the 75R that connects pin 1 to GND. It might be too low.

Use a multimeter and measure the resistance between pin 1 of the vga connector and GND .. it should be close to 75ohm..  if it is near zero then something is wrong, either a short (solder splash) (look very closely at the connector) there are GNDs near the pin 1..  

Regards,

Mik
Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
matherp
Guru

Joined: 11/12/2012
Location: United Kingdom
Posts: 10315
Posted: 01:51pm 30 Aug 2020
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Type CLS RGB(RED) and you should measure around 0.7V on pin 1. If that looks OK then it is the cable
 
bar1010
Senior Member

Joined: 10/08/2020
Location: United States
Posts: 197
Posted: 09:16pm 04 Sep 2020
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  TassyJim said  Most likely point of failure is

Your cable
Socket where it's soldered onto the board.
Shorted 75 ohm resistor
Short or open circuit trace from socket to resistor networks.

The pins on the CPU are not likely because there are 5 and failure of all is not plausible.




Jim


As it turns out my VGA to VGA cable was bad.  Received a replacement cable today and now the Red color appears on the intro screen along with the other correct colors.  Thanks a lot for the ideas.
 
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