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

You mean missing red ?

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

It is less likely for the color decoder to cause the loss of a color than s omething 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 inform ation 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 resi stor or sometning to a pin on an IC or transistor. If there are three ICs y ou can swap them to ind the fault, but alot of them use one IC for all colo rs. Or it could have three transistors. If you can get a good picture of th e CRT board (where the socket is), I can probably sort out what's what if y ou don't do well at reverse engineering.

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

uitry. 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 gri d I guess) and one more which reads 0 (filament on AC?) And focus of course.

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 info rmation on it, you can see there ar three identical things going to three o f the pins. Those will be the cathodes. You should see eacj go through a re sistor 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 co lors. 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 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

Got a soldering iron?

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 r ed 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 b ecause we haven't determined what kind of power supply this thing has. Is m ight 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 curr ent. Once you see the color that is enough. In fact go ahead and try the bl ue 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.

t 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 t he 10 K is pulling the red cathode voltage down below the other two. Once y ou 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. I f the 10 K doesn't pull it down to like 50 volts, try maybe an 8.2 K.

rrent. 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 ha ve to be around the TDA3565, but I cannot see what it can be at the moment.

t 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 t he 10 K is pulling the red cathode voltage down below the other two. Once y ou 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. I f the 10 K doesn't pull it down to like 50 volts, try maybe an 8.2 K.

rrent. 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 c annot fint anything that seems to wrong. It is not the exact same as the da tasheet, 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 str ong. some of them are a really pure blue which inherently requires more cur rent to push. The only tubes that had the really ineffieicent red phosphors were from the 1950s and abouts. then they found neodynium or someting, thr ew 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 mi ght 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.

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.

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