5" monitor, showing only green (and sometimes blue) [TDA3565

Hi all

I have got this small monitor (and TV which I dont use). It only shows a green picture.
Sometimes, it get blueish but I cannot keep that or measure on that. But that and that all 3 filaments work makes me think that the CRT is ok
The picture is sharp and nice, but only green.

It is build on TDA4505 and TDA3565 (pal and colour decoder).

The TDA3565 has its frequencies (but the 8.8Mhz seems a bit higher), and I can adjust pin 5 (color) 1.5-2.2V which is clearly visible on the RGB outputs. A wild guess is that it is somewhat working.

From the TDA3565 3 transistors are driveing the CRT. Both TDA3565 and transistors are replaced, but I still have this problem. All eletrolytes are replaced.

Since I find it hard to believe that the CRT is broken, what could it possible be?
The set is so simple that I cannot see what it can be.

WBR
Sonnich

 

You mean missing red ?

Cathode voltages. If the red cathode voltage is higher, it is in the circuitry. If it is lower it is the CRT.

It is less likely for the color decoder to cause the loss of a color than something in the video output circuitry, usually mounted on a board right on the CRT socket. That is the main place to check. If you do not have information on it, you can see there ar three identical things going to three of the pins. Those will be the cathodes. You should see eacj go through a resistor or sometning to a pin on an IC or transistor. If there are three ICs you can swap them to ind the fault, but alot of them use one IC for all colors. Or it could have three transistors. If you can get a good picture of the CRT board (where the socket is), I can probably sort out what's what if you don't do well at reverse engineering.

 

On Monday, November 3, 2014 11:17:18 PM UTC+2, jurb...@gmail.com wrote:
> You mean missing red ?

Well, I have seen blue shades now and then, but right now I dont. only green.

Cathode voltages. If the red cathode voltage is higher, it is in the circuitry. If it is lower it is the CRT.

RGB are DC: 76 - 68 - 72V
By scope: 60-100, 45-95, 60-100

According to your theory the CRT is then ok.
There are only a few other pins in use - 2 grounded, one has 135V (some grid I guess) and one more which reads 0 (filament on AC?)
And focus of course.

It is less likely for the color decoder to cause the loss of a color than something in the video output circuitry, usually mounted on a board right on the CRT socket. That is the main place to check. If you do not have information on it, you can see there ar three identical things going to three of the pins. Those will be the cathodes. You should see eacj go through a resistor or sometning to a pin on an IC or transistor. If there are three ICs you can swap them to ind the fault, but alot of them use one IC for all colors. Or it could have three transistors. If you can get a good picture of the CRT board (where the socket is), I can probably sort out what's what if you don't do well at reverse engineering.

The TDA3565 is mounted in the base board, which 3 wires to the transistors on the CRT board - they were C2229 but not are NTE287. Both the TDA3563 and transistors are replaced with new ones.

I wonder how I can turn off the green to see if I have any other colour

WBR
Sonnich

 

The TDA3565 is mounted in the base board, which 3 wires to the transistors on the CRT board - they were C2229 but not are NTE287. Both the TDA3563 and transistors are replaced with new ones.

The on-line cross reference has NTE399 as the replacement for a 2SC2229.
While the characteristics are similar in many cases, I would use the corerct sub first.

Dan

 

"RGB are DC: 76 - 68 - 72V
By scope: 60-100, 45-95, 60-100

According to your theory the CRT is then ok. "

Not necessarily. I as expecting to see the red cathode alot higher.

Since you have dicrete video outputs and not a chip you can clip lead test it. Turn your brightness/cpntrasdty down and tak a 10 K resistor from the red cathode to ground. You should see red. Use a voltmeter and make sure the 10 K is pulling the red cathode voltage down below the other two. Once you see red get it off of there, in fact just stick the resistor in the end of a grounded clip lead. Use the connection to the CRT aquadag for a ground because we haven't determined what kind of power supply this thing has. Is might not be totally isolated, and you don't want to use the hot ground. If the 10 K doesn't pull it down to like 50 volts, try maybe an 8.2 K.

Only connect this temporarily as it might result in excessive cathode current. Once you see the color that is enough. In fact go ahead and try the blue as well. Once the CRT is actually confirmed good, then it is a matter of working backwards.

 

Reason for the cliplead test is because CRTs are not created equal, and neither are the three guns or phosphors in one. Some seem to swing to full on with like a 30 volt drop, others take 100.

 

[William Sommerwerck]

> I wonder how I can turn off the green to see if I have any other colour.

Got a soldering iron?

 

On Wednesday, November 5, 2014 2:35:30 AM UTC+2, jurb...@gmail.com wrote:

"RGB are DC: 76 - 68 - 72V
By scope: 60-100, 45-95, 60-100

According to your theory the CRT is then ok. "

Not necessarily. I as expecting to see the red cathode alot higher.

Since you have dicrete video outputs and not a chip you can clip lead test it. Turn your brightness/cpntrasdty down and tak a 10 K resistor from the red cathode to ground. You should see red. Use a voltmeter and make sure the 10 K is pulling the red cathode voltage down below the other two. Once you see red get it off of there, in fact just stick the resistor in the end of a grounded clip lead. Use the connection to the CRT aquadag for a ground because we haven't determined what kind of power supply this thing has. Is might not be totally isolated, and you don't want to use the hot ground. If the 10 K doesn't pull it down to like 50 volts, try maybe an 8.2 K.

Only connect this temporarily as it might result in excessive cathode current. Once you see the color that is enough. In fact go ahead and try the blue as well. Once the CRT is actually confirmed good, then it is a matter of working backwards.

I tried the colours, and they are all there.
Now I tried another video source, and it does not work. The problem will have to be around the TDA3565, but I cannot see what it can be at the moment.

 

On Wednesday, November 5, 2014 2:35:30 AM UTC+2, jurb...@gmail.com wrote:

"RGB are DC: 76 - 68 - 72V
By scope: 60-100, 45-95, 60-100

According to your theory the CRT is then ok. "

Not necessarily. I as expecting to see the red cathode alot higher.

Since you have dicrete video outputs and not a chip you can clip lead test it. Turn your brightness/cpntrasdty down and tak a 10 K resistor from the red cathode to ground. You should see red. Use a voltmeter and make sure the 10 K is pulling the red cathode voltage down below the other two. Once you see red get it off of there, in fact just stick the resistor in the end of a grounded clip lead. Use the connection to the CRT aquadag for a ground because we haven't determined what kind of power supply this thing has. Is might not be totally isolated, and you don't want to use the hot ground. If the 10 K doesn't pull it down to like 50 volts, try maybe an 8.2 K.

Only connect this temporarily as it might result in excessive cathode current. Once you see the color that is enough. In fact go ahead and try the blue as well. Once the CRT is actually confirmed good, then it is a matter of working backwards.

ok, I tried to check all wirering around the TDA3565 and signaling, and I cannot fint anything that seems to wrong. It is not the exact same as the datasheet, but close. No shorted condensators, resistors seem be ok.

Using my scope I have signals which seem to be ok. The contrast voltage can be adjusted (pin 6), but it has no affect whatever.

Maybe afterall it is the CRT

 

Scope it right at the CRT cathodes.

If the thing is not old enough for aa pension (literally) it has all common elements of the tube except the cathodes. That is now the inpur no matter what.

I should've told you to do the green cathode with the resistor as well. If the green is really bright and the red is not, it is probably the CRT. With the same resistor, the red should be every bit as bright as the green, and maybe brighter. The blue not so much, some blue phosphors are not that strong. some of them are a really pure blue which inherently requires more current to push. The only tubes that had the really ineffieicent red phosphors were from the 1950s and abouts. then they found neodynium or someting, threw it in the phosphor and red was brilliant after that. Now if there is any problem, it is the blue.

Have you found the greyscale adjustments ? You know if it is the CRT, it might still be within limits to adjust. We used to do that all the time. You could have pots on the board or you could have it in the service menu.

It is normal for CRTs to become imbalanced over time, that is why there are adjustments.

 

[Jeroni Paul]

And on some occasions I have balanced worn tubes when the adjustments do not allow replacing some resistors to either brighten the worn color or darken the dominating color.

 

On Monday, November 3, 2014 10:55:20 PM UTC+2, sonnic...@gmail.com wrote:

Hi all

I have got this small monitor (and TV which I dont use). It only shows a green picture.
Sometimes, it get blueish but I cannot keep that or measure on that. But that and that all 3 filaments work makes me think that the CRT is ok
The picture is sharp and nice, but only green.

It is build on TDA4505 and TDA3565 (pal and colour decoder).

The TDA3565 has its frequencies (but the 8.8Mhz seems a bit higher), and I can adjust pin 5 (color) 1.5-2.2V which is clearly visible on the RGB outputs. A wild guess is that it is somewhat working.

From the TDA3565 3 transistors are driveing the CRT. Both TDA3565 and transistors are replaced, but I still have this problem. All eletrolytes are replaced.

Since I find it hard to believe that the CRT is broken, what could it possible be?
The set is so simple that I cannot see what it can be.

WBR
Sonnich

Well I found it.

The TDA3565 has a potentiometer for the burst (pin 17, see datasheet)
It wasnt connecting well, so when I turned it I got my colours back.

However....
hot.ee/sonnich/Photo3024.jpg
The border should be red, but is red/green. Why I get this I dont know.
Sometimes they "run"

By turning the potentiometer I can get rid of that and get red.

Still red is not to strong, so I turn it more on then it work, but that also causes orange to become quite red.
This is not so important, it can be used as it is now.

Still, I dont get the green/red colour rows



WBR
Sonnich