[SOLVED] Coloured retrace lines on top of the picture, Sony BE4A chassis KV21T1D

Hello,

I have a BE4A chassis Sony Trinitron KV-21T1D model CRT TV. Everything is normal on TV except red, green and blue retrace lines on top of the picture. I attached a picture to show the actual situation. On the photo which i took, only red and green lines are appearing but if i move Vertical center through bottom, or contract Vertical size more, blue becomes visible too. Lines are appearing independent of source (TV, AV, even on AV mode when there is no input connected) Adjusting of Screen setting have very little effect on the appearance of the lines. Looks like something is wrong with blanking or vertical deflection circuits, but i wanted to ask before doing something in case of the possibility of the fault as a known fault on these TVs.

Thank you for your support.

It's not circuit problem. Your picture tube has been defective. I have a conciliation to solve this. Appear picture by weird collection of cathode rays. The most extreme deflection occurs when the magnet is close to the beam and the poles are facing outwards. If the south pole is facing out the beams is deflected down. When the north pole is facing out the beam is deflected upwards. Power on your TV & slew a magnet nearest tube. May be it will work.

I disagree. It's a capacitor in your vertical deflection circuit. Without a schematic I will be unable to help further. Typically there is a capacitor in series with your vertical yoke coil which charges while
the yoke current is pulling your scan line down to the bottom of the screen then during the short retrace interval the capacitor provides the boost current to quickly move the scan line to the top of the screen during the blanking interval while the CRT gun is turned off. With a weak capacitor, the scan is not moved to the top within the blanking interval so the gun turns back on before the scan is at the top and you see a few retrace lines. I've serviced many televisions in the past and this has been the case. It is just a matter of identifying which capacitor.

Found the schematic !!! C504 100uf 50v is charged thru D501 to like 26V to effectively provide the boost current to the vertical deflection IC501 output stage. I knew if I saw a schematic I would recognize the faulty capacitor.

Larry G

Magnetic disturbance would manifest itself as a purity error and the picture geometry would be twisted. This looks more like the start of vertical retrace isn't being blanked properly or the scan signal is drooping, an electrical fault.

Try what Larry suggests, if it isn't that the fault will be in the retrace blanking circuits.

If Larry found the same schematic I did, it is very confusing - scanned in narrow sections with half of them upside down! Very difficult to follow when lines route from one page to another!

Brian.

First of all, thank you for your quick answers.

@Ranbeer Singh
I dont think tube is defective, because if i reduce the levels of colours using service menu, brightness of the retrace lines are reducing at the same level.

@retrogear
I uploaded a better schematic. At least part of it is not upside-down and easy to track the lines if you look using double page (side-by-side) mode on acrobat reader.


@betwixt
Yeah, there is no purity problem and convergence is also good. Geometry is OK too. If Larry's solution doesnt work, i'll look at there. But blanking circuit on this TV seems to be managed by microcontrollers (IC001, IC301), could EEPROM needs to be reprogrammed?

Onur

retrogear said:

I disagree. It's a capacitor in your vertical deflection circuit. Without a schematic I will be unable to help further. Typically there is a capacitor in series with your vertical yoke coil which charges while
the yoke current is pulling your scan line down to the bottom of the screen then during the short retrace interval the capacitor provides the boost current to quickly move the scan line to the top of the screen during the blanking interval while the CRT gun is turned off. With a weak capacitor, the scan is not moved to the top within the blanking interval so the gun turns back on before the scan is at the top and you see a few retrace lines. I've serviced many televisions in the past and this has been the case. It is just a matter of identifying which capacitor.

Found the schematic !!! C504 100uf 50v is charged thru D501 to like 26V to effectively provide the boost current to the vertical deflection IC501 output stage. I knew if I saw a schematic I would recognize the faulty capacitor.

Larry G

Click to expand...

I replaced all electrolytic capacitors in vertical deflection circuit, including C504. But unfortunately nothing changed. Retrace lines are still there. I found some weak solders and re-soldered them all on several parts of the board, including power supply, horizontal deflection, vertical deflection sections and tube drive board. Again nothing changed. I think problem is somewhere around system control and chroma IC's.

I have another (actually more annoying than retrace lines) problem too. Faint horizontal lines appearing on picture intermittently. But lines are not solid, they are like interference lines and not steady, always moving from bottom to top at different speeds depending on vertical refresh rate (I'm using TV as a monitor connected to PC from Scart, and depending on selected video mode, refresh rate could be set between 50 to 61 Hz) They are sometimes stronger, sometimes weaker.
Sometimes, lines appearing when TV is cold (when just turned on), sometimes after some usage. So it is not looks like related with heating of some component. Both AV and TV modes are affected. Lines could be noticed on OSD too (black screen with green OSD) when there is nothing connected to the TV (no scart connection, no antenna) so i eliminated the ground loop possibility. Today, i saw a description of a similar problem in another thread and saw that reservoir capacitor could be the reason. Where should i search the fault?

PS-Fault was there before changing vertical deflection capacitors too, it is not related with the job performed to solve retrace line fault.

IC501 pin 2 should be 24 volts. Can you measure that and confirm?

Larry G

retrogear said:

IC501 pin 2 should be 24 volts. Can you measure that and confirm?

Larry G

Click to expand...

IC501 pin2 measures 28.80-28.95 V DC. I measured all other supply voltages too. These are:

190V: 191.0 V
135V: 135.1V
5V: 4.82V
8V: 8.58V
18V (also defined as 21V on some parts of the schematic): 20.28V

24V seems to be derived from FBT, and input votage (135V) of FBT is perfect. R814-C819-D806 and C820 are the rectifying-filtering components of 24V. C502 and C503 are the caps near vertical IC. Any of them (especially C820 470 uF 35V) could be faulty?

***********
About moving lines (hum bars?) apperaing intermittently on screen: I connected an external antenna and received a channel (PAL) I observed two lines (two because rectified 50Hz mains=100 Hz?) and lines were almost steady or just moving slowly up and down. Now, i replaced the most suspected part, main filter capacitor (C606 180uF 400V) with a 220 uF 400V cap. TV is operating for one hour and i didnt observed these lines yet.

Update:
- I replaced C820, nothing changed.
- Two horizontal lines appeared again after 5-6 hours of use.

C503 is a possibility. What is the voltage on IC501 pin 6? Since pin 2 is roughly 29V then pin 6 must be a couple volts higher like 31-32V. If not, since you already
replaced C504 then maybe D501 is open? The max drop across D501 can only be .6V so pin 6 has to be > 28 volts or so. Also is your image centered vertically?
Try rocking RV801 to move image vertically up/down. Do the lines increase or decrease? Has the problem always shown up after on for a few hours? That would be
thermal related. Could try cooling individual components.

Larry G

I just noticed you spoke of AC hum crawl. It shouldn't be related to your retrace problem.
The lines I was talking about watching with the vertical centering is the retrace lines.
Like I spoke of in another thread about AC hum, measure the AC voltage across C606. Should be only a couple volts. See if AC voltage changes when hum lines come and go.

Larry G

Sorry, i expressed the problems a little bit unclear. I have two unrelated problems.

About the first problem (retrace lines on top of the picture):
I'll check the voltage on pin 6 and D501 soon. Image is centered vertically. If i move the centering pot, lines are moving together with image. If i adjust Vsize using service menu, lines are also moving at the same amount (i can hide them by adjusting Vsize a bit more, but in this case i'm losing the picture from top and bottom at some resolutions.) If i switch aspect ratio to 16:9 mode, lines are completely disappearing. They are always there at the beginning of the operation and they neither increase nor decrease with time / heating.

*********************************************************

About the second problem:
Moving horizontal lines appears or disappears intermittently. After the change of main filter capacitor C606 (180 uF 400V) lines were not there for 5-6 hours but then appeared again. I guess it was not related with that capacitor.
I'm building an in circuit capacitance/ESR meter to check each cap on TV chassis. It is almost a 20 years old TV with all original parts so possibility of a failure could be expected.

At PAL (50Hz) broadcast, they are almost steady, just moving slowly up or down. And there are definitely two lines on screen at the same time)
At 60 Hz signal feeded from scart, lines are always moving from bottom to top.

I made some pics and videos which are showing the problem clearly.

at 60 Hz signal (since the lines are moving faster, it was hard to photo. Thats why lines are looking fainter than 50Hz ones on photos):


https://www.dropbox.com/s/huwp5ns5oxbha1y/60Hz.wmv?dl=0

at 50 Hz PAL broadcast (signal is weak because i used an indoor antenna, thats why image is noisy):

Is the distortion worse on the right hand side of the screen? If so, that would indicate a horizontal component to the problem. If the vertical drive has some distortion, it could get introduced into the horizontal
drive via the pincushion correction circuit. However, that shouldn't be floating thru the screen but it sure doesn't look like AC hum either. Maybe fixing the vertical retrace problem will fix this too. Let's focus on the retrace problem. I have seen a problem like you're showing now but it's been many years ago so I don't remember.

Just saw your note about no retrace lines in 16:9 ratio. I'm assuming in that mode it doesn't fill the screen vertically, so you have black space at top and bottom - correct? If so, that confirms problem is vertical deflection circuit because less amplitude vertical drive to the yoke. I would think a blanking circuit problem would still produce retrace lines in 16:9 display area.

Larry G

Distortion is equal on left and right sides, but center of the screen is almost free from distortion. (first three pics are showing only upper-right part of the screen, not the whole) I've sent you links of three videos recorded at TV broadcast via pm. In these videos distortion is clearly visible)

in 16:9 mode, it doesn't fill the screen as you said. There are black sections on top and bottom of the picture. But i made an experiment at this mode as follows: I increased vertical size using service menu to fit image full screen (without black spaces) at 16:9 mode (at 4:3 mode image is vertically overscanned) By doing this, retrace lines disappeared and i've got a full screen picture. Of course this is not a perfect solution, it just hides the problem.

As this is a CRT television, I would guess the distorton is some instability in the E-W corection circuit. I'll have to download the schematics again to check but it seems a likely candidate.

Brian.

Hi Brian,

You can find the schematic on my 2nd post. I re-orineted the pages to ease tracking at 2-page side by side mode on acrobat reader.

You can watch the video below too (but you need to watch after download since dropbox applies a conversion which reduces quality and hides the lines) I have two more video, in which the lines are more apparent but i recorded them during an advertisement so publishing of these links seems to be forbidden in thread.

https://www.dropbox.com/s/ph03kh7tcoqi6u1/50Hz-1.wmv?dl=0

Yes, distortion left and right edges vs. center is E-W correction which I think is the same as pincushion but different terminology?
The fact it is on left and right edges definitely points to it.
The problem may not be vertical deflection, however for my curiosity put the NEO-GEO image back on the screen which shows the
retrace at top and measure DC on IC501 pins 2 and 6. Pin 6 has to be higher DC than pin 2 for the boost to work. Insufficient vertical drive
could introduce the E-W distortion if they are modulating the horizontal drive with correction from the vertical drive. Maybe I'm too old fashioned
and later televisions did it a more sophisticated way. I was not servicing TV's after HD was on the scene. Think of vertical drive as a line at a 45 degree
upward angle which at the top suddenly drops to the bottom like the jagged edge of a sawtooth blade. The boost circuit helps it reach the very point at the
top of the tooth which corresponds to the top of your display and over the top slightly. Without that, it kind of curves down and exposes the top.


Larry

Yes, pincushion and east-west should be the same thing if i remember right too.

I'll check the voltage of IC501 between pins 2 and 6. Horizontal drive and vertical drive has some connection between (L804, Q804-Q805 and other components shown near vertical IC on schematic.) for pincushion correction. Drive signal comes from IC301 pin 8 P-DRV {also defined as E-W drive on datasheet of MC44002P}

If it will help, i have an oscilloscope and i can trace signals like vertical drive etc.

Oh my, if I knew you had a scope !! Use DC coupling, vertical rate and first put on IC501 pin 2. Keep decreasing volts/div and move trace down to keep in middle of display on scope. Adjust trigger so ripple is locked. Then put probe on pin 6 and the peak DC of waveform should be a couple volts HIGHER. Then you can do the same for the lowest point DC on both pins. The lowest point DC on pin 6 should be .6 VDC LOWER than pin 2.

The theory should work like this - as pin 3 voltage goes low, C504 is charged from VSS pin 2 through D501. As the drive brings pin 3 high, the charge on C504 is added to pin 3 which pushes the VSOS supply voltage pin 6 up higher than VSS to provide boost current to the vertical yoke to push the display to top of the screen. If you want, you can just post pictures of the scope waveforms of those pins but be sure to use DC coupling because it is important info. Of course, the AC ripple on pin 2 should be quite low if C503 is good. I would say if 29VDC is on pin 2, AC should be < .5V and maybe only a tenth or two.

I will make the measurement and post the results and pictures on saturday.