Vertical distortion at left side of monitor screen

[rfmw]

Monitor, model CM-735, manufacturer unknown (probably AOC or Envision) started to show distorted picture on the screen.

At left-hand side of the screen there is vertical distortion (like damped sinewave), shown on the picture bellow.

I couldn't find this 1-2 % distortion using oscilloscope and measuring vertical deflection chip TDA1675...

Do you have any idea, what could be wrong with the monitor?

Thanks,
rfmw

**broken link removed**

 

[VVV]

I've never seen anything like it, but since ist is synchronized with the H-deflection I suspect a decoupling capacitor.
I would first check with the scope the voltage on the power pin of the TDA1675, and make sure there is no significant H-frequency ripple.
Next, I would check with the scope all the voltages out of the power supply, across all of the electrolytic capacitors.
My money is on one electrolytic capacitor gone bad that now has large ripple.

 

[rfmw]

Actually, I've found on the Internet a similar problem (and solution) with one of the Mitsubishi TVs. The problem with the TV was that 330uF/450V at graetz bridge had gone bad and such vertical distortion appeared. Perhaps my monitor has the same problem, but I don't have such electrlityc capacitors laying around the table...

The power rail of the TDA 1675 is 27V and has approx 1Vpp low freq (not H-freq)ripple. I've added across another 1000uF capacitor to lower the ripple, but the problem was the same, no improvement at all.

Yeah, I've measured all power supply voltages with digital volt meter and not with oscilloscope and all voltages were OK. Measuring the ripple on these power lines is a good idea and I'll try that asap.

How pure should be the V-yoke current? It has some high freq (i guess H-freq) ripple, but then it would be distorted the whole picture and not only at left-hand side of monitor...

Thanks for your suggestions and help. Everything helps

cheers,
rfmw