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[Solved] Did I permanently damage my CRT with out-of-range signal?
rogerxyz:
Thank you, Butters and Zeb, for your consistently insightful feedback and your eagerness to share your wisdom!
First things first, let me just untie the grounds from the PC and TV and see what happens. I will report back. I thought we were okay here since they are both on the same mains circuit and we're talking about the low-voltage side of the trinitron motherboard, but this is what you get when you have armchair electronics idiots like myself who are handy with an iron but have never learned anything past Ohm's law.
As for it being an input issue (e.g. external to the chassis) I think we can rule this out since I can see this pattern when the tube is dim on completely other inputs and even when disconnecting any inputs.
Hopefully it's just my dumb mistake tying the power switches. Fingers crossed.
rogerxyz:
No real luck leaving my extended leads to the front panel's power tact switch floating, I'll get to work removing the trinitron's main board and undoing my work there nonetheless.
--- Quote ---Another thing to keep in mind is that TV power switches usually have a mains voltage part that physically switches power on or off, and also a logic-voltage momentary part to tell the TV to come out of standby. You don't want to get them mixed up.
--- End quote ---
I tapped into the little tactile momentary power switch button on the front panel, in the control cluster with the other physical controls Vol/Channel/Menu/etc., I was under the impression that was more of a soft/logic level switch, gosh I really hope I didn't make a dumb assumption. :(
I want to correct that the issue is visible with no input, that's not correct. It's definitely dependent on sync as the pattern changes between video modes. But on disconnecting the Pr component, the traces are still there and still red, if that affords any information. Swapping out the input with a playstation 2 using the same component connections exhibits the same red scanlines on dark screens.
Will report back after reconnecting the main board to the neckboard, I'll use that time to check all the connections more thoroughly, though I did a cursory check before. Thanks for sticking with me.
EDIT 1: It's also worth reiterating that I somehow created this issue the last time I opened the cabinet; I did not notice it before. It seems less likely then that this would be down to a cold solder joint but I don't want to rule anything out. 🙏
EDIT 2: I was thinking, and I was like "would I really have tied the PC and monitor together?" and I remembered, no, I checked that the switch was DPST first. I re-verified this just now. So I don't think they were ever on the same circuit. (I do a quick flip to ON/closed and back instead of leaving it toggled, to mimic the momentary switches on the PC and monitor)
EDIT 3: I should emphasize that the photo I've shown was taken in complete darkness to better illustrate. In reality the flood and travel lines are very faint. And again, only visible on a screen that's mostly or totally black.
--- Quote ---Assuming you have tried simply turning down the red bias
--- End quote ---
This should be a simple enough thing to try; is this equivalent to adjusting the "R Drive"/"RDRV" in the service menu? Won't that affect the picture overall? I also seem to have access to "R Cutoff" lower and upper thresholds, if those would be useful.
buttersoft:
Drive is gain is highlights or the brightest part of the signal. This is often called contrast when talking about all three colours at once.
Bias is cutoff is lowlight, or the background level of the signal. This is brightness when talking about all three colours at once.
Here, with no signal, you're getting a red tone, so you want to lower the red cutoff level. Hopefully that helps.
Zebidee:
Good luck with the neckboard, I hope you can find the cause of the issue. I think we've given you as much advice as we can, so far.
Sometimes TVs do separate the mains power switch and the control circuit momentary button, like you described.
I won't worry you anymore about your original switching arrangements - if it is related to the red overdrive issue you're having, I don't know how, and in any case you have dismantled it.
As promised: one simple way to simulate a button press & release on connecting power is with a basic time delay circuit, which is just a resistor and a capacitor:
- solder a resistor (for this example I'll use a 1000 ohm or 1k resistor) to the positive lead (+, longer) of an electrolytic capacitor (for this example I'll use 100uF), so that the resistor and capacitor are now together. Now solder the resistor end to the momentary switch's active terminal, and the negative end of the capacitor to the ground terminal. It'll look like this:
Active---------[resistor]------[ + capacitor - ]------GND
When you apply power, this will initially be a closed circuit (like you have pressed the button in), but within a short time the capacitor will become charged and then it will block the current, acting like an open circuit (like you released the button). The capacitor just gives you a short delay before the button "release", literally a fraction of a second, giving your TV control circuits some time to wake up and register the button release.
You can control the time delay by adding/changing the value of the resistor, with a larger resistor giving you more time delay. You can also extend the delay with a larger capacitor, but it is easier to change the resistor (or use a pot). If you want to know the math:
T = R x C
Plugging in the example values of 1000 ohms and 100uF (micro farads, so really 0.000100), we get:
T (seconds) = 1000 x 0.000100
T = 0.1 seconds
Obviously if we used a 10k resistor instead then you should get a longer 1 second delay (which should be more than enough). If you wanted to work out what values work for your TV, try using substituting a 10k pot for the resistor and dial it in. Once you are happy with the pot setting, replace it with the appropriate resistor value.
Some caveats:
- This may work fine even without a resistor, there will still be some short delay as the cap charges initially and larger caps take longer to charge.
- If a resistor value is too high it may prevent the control circuit from properly registering the "press". So start with a lower resistor value and work up.
- Be aware that not all grounds are the same on a TV, esp between the HOT and COLD sides. If you aren't 100% sure then probably best to take your GND back to the relevant spot for the original button at the control circuit.
- 1/4 watt resistor and 16v capacitor ratings should be sufficient, but...
- Appropriate resistor and cap values may vary for different TVs.
- Might not work with every TV. For example, some TVs may want to register the circuit as "open-closed-open", this only gives you "closed-open", if that makes sense.
- This is a hack. If you do this, you do it at your own risk. If your TV blows up then don't blame me.
There are some other ways to get the TV to come on once you apply power, such as using a 555 timer and a relay, but this is by far the simplest.
I've assumed, with the above, that your TV won't come on automatically when you apply power. If it does come on anyway then just ignore everything I've just said and go buy a smart strip with master/slave outlets, and plug PC into the master, TV into slave. Or use a relay.
bobbyb13:
Whew!
I'll need to read this a few more times for some more to stick.
The technical knowhow of a number of you here still stuns me.