VOGONS


First post, by westygw

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Hi. This is a real shot in the dark.. but maybe someone can help.

I've got this new CRT I picked up- a Compaq P1210 (HP P1210).
On my DOS PC the image is flawless and stunning.
On my Windows 10 PC, the image has dramatic vertical foldover on the top 1-2" of the display.
This folding is associated with a high pitched whine coming from inside the monitor.
Lowering refresh rate does reduce the foldover and reduce the noise, but it occurs at all resolutions and at any refresh rate.
I can eliminate the folding by lowering the desktop position in the Nvidia settings and then raise the vertical image on the monitor but this also takes 1-2" of the desktop (taskbar) out of bounds of the display.
I've tried multiple modern PC's and switching between native VGA output as well as a DVI-I to VGA converter. Nothing fixes it. Again, it works just fine on my 486 machine all the way up to 1024x768.
The same resolution (1024x768) on my desktop shows the vertical foldover.
After disassembling the monitor I noticed no leaky capacitors or any signs of bulging. Everything is dusty, but in otherwise good shape. The noise isn't coming from the flyback transformer.. but from the circuit board covered in a plastic cover on top of the tube.
Poking the circuit board with a big (nonconductive) stick results in the whine changing pitch and the folding to either increase or decrease in severity.
I'm at a real loss here and nothing seems to alleviate this. If anyone has any shred of a clue what might be causing this, I'd love to hear about it.

I'm uploading a picture of a monitor (just a random one off Google) and highlighting the area where the loud whine comes from.

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Reply 1 of 5, by 133MHz

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If flexing the circuit board changes the symptom then you have cracked/cold solder joints somewhere in the vertical deflection circuitry. You should take a good look at the board and reflow every solder joint that looks even slightly off, that will likely cure the problem. If not, then you probably have a bad capacitor in the vertical stage (even if nothing's visibly bulging or leaking).

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Reply 2 of 5, by westygw

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I'm gonna carefully remove that circuit board here soon and check everything over. Hopefully it is just a cracked joint that I can fix easily.
The loud noise is definitely coming from this little plastic container (not sure what's inside) on the circuit board, or from underneath it. It doesn't appear to be a coil.. but it looks as if it's some sort of glass fuse holder, or something.

Reply 3 of 5, by 133MHz

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Under that plastic shell you'll find more coils, potentiometers, some resistors among other passive components for more complex geometry correction. The yoke normally buzzes at the frame rate frequency like a crude speaker, so if it's being improperly driven because of a fault it will buzz/whine even more. If you're flexing something and you see stuff changing, there's definitely something loose somewhere.

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Reply 4 of 5, by CkRtech

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Hey westygw - You probably already know this (I am assuming due to your familiarity with CRT terms, etc), but I just wanted to make sure you are aware of how to properly discharge a CRT (and that it involves more than just the anode from the flyback).

Or perhaps for someone else that stumbles across this thread.

Displaced Gamers (YouTube) - DOS Gaming Aspect Ratio - 320x200 || The History of 240p || Dithering on the Sega Genesis with Composite Video

Reply 5 of 5, by westygw

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CkRtech wrote:

Hey westygw - You probably already know this (I am assuming due to your familiarity with CRT terms, etc), but I just wanted to make sure you are aware of how to properly discharge a CRT (and that it involves more than just the anode from the flyback).

Or perhaps for someone else that stumbles across this thread.

I'm pretty aware of the dangers involved. I've been zapped by a few CRT's.. but the real scare comes from those lower voltage components that won't hesitate to discharge through your heart.
I'll spend some time discharging everything when I get some time and space to take it all apart. This thing is so huge I have to basically clear out a room to work on it.