SONY CPD-E400P overbrightness and visible retrace lines

[kralg]

Hi, I am trying to save my old monitor once I was so proud of. I hope there are still some people around with experience.

Symptoms: overbrightness and visible retrace lines. When full white image is displayed, the monitors shuts off with flashing yellow.

I have read previous threads and posts with similar issue, but none of the solutions can be applied to my monitor. According to them I need to suspect the G2 voltage as the issue.

I attached the page of the A board schematic. In my case the G2 voltage supply coming from the flyback transformer is supposed to be 1kV and I measured 938V with my multimeter. The exact applied G2 voltage is controlled by the MCU through the RGB preamplifier. Additionally there is a delay circuit that pulls this voltage slightly lower initially which effect vanish after half an hour or so. And here comes the confusion. The schematic says the G2 voltage is supposed to be 615 V (as seen on Q1 collector). I also happen to have the training manual for the CPD-G400, (which is basically the same monitor with multiple VGA inputs) and on the G2 control page (attached) it says that cold G2 voltage is supposed to be 660 V. After half an hour it increases to 667 V. Now, in my case the cold voltage is 674 V and after half an hour it goes to 685 V. It is much higher than 615V, but quite close to 667V. Which one may be right? The G2 control voltage (coming from the RGB preamplifier) is measured as 2.39V which is almost exactly 2.38V as specified. All in all, the G2 related circuits seem to work fine, I am not even sure that the voltage is too high.

Any ideas? And is it possible to check the exact reason for malfunction when I switch to aging mode (full white screen)?

(Of course I checked the power supply lines as well. I have all voltages, though all of them is slightly lower. Like 200V -> 197V, 80V -> 77V, 12V -> 11.7V etc.)

[R_J]

Re: SONY CPD-E400P overbrightness and visible retrace lines

Sometimes it is just the cap near the high voltage transformer on the 200v supply that is the problem. C506 (22µf/250v)
Another cap to check is in the power supply on the 80v supply C623 (100µf/100v)
Another one that gave problems on some models was for the heater supply (C626)

[kralg]

Re: SONY CPD-E400P overbrightness and visible retrace lines

Thanks for the response. I will check the 200V there with my scope, but I cannot see how that cap could be related to the retrace lines as that part has something to do with the horizontal deflection.

[kralg]

Re: SONY CPD-E400P overbrightness and visible retrace lines

Sometimes it is just the cap near the high voltage transformer on the 200v supply that is the problem. C506 (22µf/250v)
Another cap to check is in the power supply on the 80v supply C623 (100µf/100v)
Another one that gave problems on some models was for the heater supply (C626)

All right, I will double check the voltages. I roughly checked with my scope and I barely saw any ripple on them. There was like a 2.5V peak-to-peak high frequency spike at 63kHz on all of them, but I guess it was just because of my probing. It is very difficult to access the D board while running the monitor.

[R_J]

Re: SONY CPD-E400P overbrightness and visible retrace lines

I didn't know you had a scope, that is the best way to check. I usually also check the ground side of the cap, that will show what the probe is picking up from the near by horz. circuit.
The last cpd-e400 I worked on was back in 2003, The ones with the bad 33µf and 47µf/200v were the cpd-e200's

[kralg]

Re: SONY CPD-E400P overbrightness and visible retrace lines

Just to close this thread I opened: after getting quite deep in understanding the operation of a CRT monitor and checking several parts of it, I found that the monitor hardware-wise is perfectly healthy.

All it needed is a recalibration using the WinDAS software. Even tough I had no colorimeter at hand for a correct calibration, I am still having an amazing image with a very nice deep black and contrast.

I know that CRT itself is a dead technology, but the electronic solutions behind it are far from it. So if anyone encounters a similar problem with a CRT (which is highly likely :-) ) I recommend giving it a look, just for fun.