Are you sure that there are no solder cracks?.
Also did you measure that all the signals from the ega cable arrives to the monitor.

If you have the monitor put together did you try to bend the ega cable from front to end in different angles to try see if there is some disconnection there.
Also the caps could be bad even if they look ok, did you try if it helps to heatup all the capacitors with blowdryer while in use.
Be sure to heatup very hot all the capacitors and see if it regains the red color, or after a restart.

Personally after a visual inspection I would just find an old tv technician and have the monitor serviced.... not much of an answer but there is a gazillion things that could be wrong with the monitor and we just guess... crts not showing one color was a common fault, should be easy for a skilled person to figure out the damage

keropi makes a good point, i understand what he is saying after i tried to revive and old projection screen TV (3 CRTS), i really count do any thing to fix it. no manual or guide could help, i even had the help of a retired TV technician and it still didn't work.

Try vintage-computer.com forums. There are a number of seasoned engineers in there and monitor repair is a fairly common topic.

First thing to check would be bad solder joints at the tube socket. Another thing to try: turn brightness all the way up. Will the background become white or cyan?

Oh, so white works, ignore my comment above. The issue is likely on the logic board (first picture).
- a resistor could be broken
- the glue for the resistors is known to eat through traces
- or a trace is broken otherwise
- bad solder joints are not always visible
- one of the logic ICs may be bad

Thank you all for your replies

JaNoZ wrote:

Are you sure that there are no solder cracks?.
Also did you measure that all the signals from the ega cable arrives at the monitor.

I can't be 100% completely sure, but visual inspection did not reveal any obvious ones. I did measure the signal for all pins and they do arrive to the other end

JaNoZ wrote:

If you have the monitor put together did you try to bend the ega cable from front to end in different angles to try see if there is some disconnection there.

See above.

JaNoZ wrote:

Also the caps could be bad even if they look ok, did you try if it helps to heatup all the capacitors with blowdryer while in use.
Be sure to heatup very hot all the capacitors and see if it regains the red color, or after a restart.

Are you saying bad capacitors start working again if heated up?

keropi wrote:

Personally after a visual inspection I would just find an old tv technician and have the monitor serviced.... not much of an answer but there is a gazillion things that could be wrong with the monitor and we just guess... crts not showing one color was a common fault, should be easy for a skilled person to figure out the damage

The problem for me is finding a shop that would do it. Most electronics stores don't service stuff this old. I'd have to find an "older" shop. I have one in my city but the guy said he charges $60 just to take a look at it with no guarantee of finding the problem.

cdoublejj wrote:

i even had the help of a retired TV technician and it still didn't work.

Exactly.

Anonymous Coward wrote:

Try vintage-computer.com forums. There are a number of seasoned engineers in there and monitor repair is a fairly common topic.

Thanks, I'll try there as well.

h-a-l-9000 wrote:

Oh, so white works, ignore my comment above. The issue is likely on the logic board (first picture). - a resistor could be brok […]
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Oh, so white works, ignore my comment above. The issue is likely on the logic board (first picture).
- a resistor could be broken
- the glue for the resistors is known to eat through traces
- or a trace is broken otherwise
- bad solder joints are not always visible
- one of the logic ICs may be bad

Can all of these IC's simply be replaced? What about the TDA3506M specifically? Is this just swappable with another one? Or is it programmed in some way first?

I will try and resolder all connections and replace all caps, see if that helps at all. I feel so bad about throwing it out 🙁

Since you get white the TDA3506M is not at fault. It's not a logic IC 😉. It controls the electron guns. Somehow the signal has to make its way from the input to the TDA3506. Red is lost on the way when it's the only active color. Your EGA card and cable are known good?

Capacitor problems show different symptoms.

h-a-l-9000 wrote:

Since you get white the TDA3506M is not at fault. It's not a logic IC 😉. It controls the electron guns. Somehow the signal has to make its way from the input to the TDA3506. Red is lost on the way when it's the only active color. Your EGA card and cable are known good?

Capacitor problems show different symptoms.

This is why I'm confused. When the switch is set to "Auto" , I can see white text. While in that mode, if I go do a color test in dos, All colors are there except Red/light red, brown/light brown. If the red color is completely missing, why is the white text, well, white? Shouldn't all three color guns fire to produce white?

I tried several EGA cards, same result, I even opened a new one just to make sure and like I mentioned above, I did a continuity test on the cable with a multimeter and signal from all pins safely arrives at the logic board.