I know 2 things about CRT/monitor repair.

1: Always discharge the unit!
2: When it doubt, replace the caps. It solves so many issues with old hardware.

Maybe this can be fixed with the tv's Service Menu , there are many options there regarding geometry - at leasts at my sets. You need to somehow get the service manual of your tv DK , maybe there is a PDF floating around

I do. Can't see the picture you posted. Is there insufficient/excessive width along with the pincushion distortion?

133MHz wrote:

I do. Can't see the picture you posted. Is there insufficient/excessive width along with the pincushion distortion?

Can you see the picture at this address?
http://imgur.com/0uyqQMX.jpg

It seems there is slightly too much width. The top and bottom are much worse than the center. Notice the checkerboard pattern at the bottom of the screen, and the palm trees on the left and right are slightly curved.

I've fidded around in the service menus, there are a number of EW controls, but they seem to make no difference. Here's the service manual: https://dl.dropboxusercontent.com/u/9151127/T … vice_manual.pdf

Indeed you have excessive picture width, poor Sonic is so far off the left he's invisible! The reason I asked that is to determine the type of failure - bad pincushion but normal width is likely to be a misadjustment due to age and/or component drift, but when picture width is severely affected your pincushion correction circuitry has failed completely, therefore as you promptly found out adjustments don't have any effect due to the non-working circuitry.

Fortunately you've come across a good quality service manual for your chassis. I've circled in red the area you should be focusing on, which is the east-west (aka pincushion) correction stage:

E/W correction in a nutshell works by modulating a compensation waveform directly into the horizontal deflection in order to counteract the inherent distortion of the electron beam hitting a non-spherical surface, in effect pre-distorting it "the other way around" so that it looks correct when displayed, much like today's VR headsets require the GPU to deform the picture sent to the LCD to counteract the optical distortion caused by the lenses in the eye-pieces. We suspect complete lack of distortion correction so we either have no input to the circuit or something has broken in the output path. Input comes from R414 from IC101 pin 45 where the correction waveform comes from, while the coupling (output) between the two stages is at the top left by L402 and R411. R411 is likely a resistor designed to fail like a fuse so it's a likely suspect for lack of output.

If there's no bad solder joints or severed traces my shotgun/I'm feeling lucky approach would be to replace R411 if found high or open circuit and C410 preferably with a 160~250V model since these tend to live a hard life and cause these kinds of problems, not a bad idea to also check L402 for continuity while you're at it. More advanced troubleshooting would involve suspecting on the rest of the components like Q401/Q402 or even the large ceramic caps on the horizontal deflection (C409/C414/C415) and checking that IC101 pin 45 is actually outputting the E/W correction waveform.

BTW is that Sega console running at 60Hz? Looks like there could be a bit too much height as well (or maybe it's just me, I tend to prefer a slightly underscanned picture for my 240p video games).

Thanks so much for the reply! If you are ever in my part of Australia, I owe you a beer.

I''ll try replacing C410 and R411 for starters and go from there.

Yes I have modded my SMS with a 50/60hz switch, in that photo it was running at 60hz. I was fiddling with v-height controls to see if it made any difference to the pincushion (obviously not!) so it probably needs adjustment as well.

I've just noticed that C410 is a bipolar electrolytic (going by how it says 'BP' on the schematic) even though it's drawn as a regular polarized capacitor, so keep that in mind and check the actual component on the board to see if it's really a bipolar cap, if it is you must replace it with a bipolar type and not a regular electrolytic.

Yes, its definitely a bipolar electrolytic.

One question before I start - if I'm only going to be replacing this cap and resistor, leaving the board in the chassis, and I'm not disconnecting the tube from the flyback transformer - do I really need to discharge the tube?

No need to discharge the tube if you aren't going near the rubber anode cap and the red high voltage wire can't be accidentally pulled out from the flyback transformer (some old Philips are like this but most flybacks are completely sealed). Health and safety, you know.. 😜

An update on my progress...

I managed to pull out the suspect cap, test it, and confirmed it is faulty... and I didn't get myself zapped in the process!
It's a 4.7uF +-10% 100V bipolar 'low wastage' (I assume that means low esr?) cap. I had a hell of a time finding a replacement, I ended up ordering this one from Mouser but it isn't low ESR, and is +-20%... I hope it will be close enough. Seems my only alternative is to solder two electro caps together in place of the single bipolar, but that will probably end up even worse for tolerance and ESR.

BTW: If those are big speakers next to the TV in the background, MOVE THEM. Having speakers close to a CRT is a really bad idea as their own magnetics may ultimately cause severe colour distortion around the edges of your tube which refuse to clear up from automatic degaussing. :P

Gemini000 wrote:

BTW: If those are big speakers next to the TV in the background, MOVE THEM. Having speakers close to a CRT is a really bad idea as their own magnetics may ultimately cause severe colour distortion around the edges of your tube which refuse to clear up from automatic degaussing. 😜

If the speaker is magnetically shielded, it really doesn't matter where it is. I had a large Sony home theatre center speaker on top of my CRT TV for 8 years and never had any distortion.

Aideka wrote:

Gemini000 wrote:

BTW: If those are big speakers next to the TV in the background, MOVE THEM. Having speakers close to a CRT is a really bad idea as their own magnetics may ultimately cause severe colour distortion around the edges of your tube which refuse to clear up from automatic degaussing. :P

If the speaker is magnetically shielded, it really doesn't matter where it is. I had a large Sony home theatre center speaker on top of my CRT TV for 8 years and never had any distortion.

Sometimes its hard to know if a speaker is shielded or not until it's too late, so if you know that ahead of time you're alright, but even then it might not be so clear cut. Mom had a couple speakers, not all that big, next to her TV in the late 90s and for months there seemed to be no issues, but then one day I was playing a game with a solid blue background and noticed a very curious and intense discolouration creeping in from one of the sides of the TV, thus discovering that the speakers Mom had were indeed shielded... but only from FIVE of its six sides, so the magnetic field emitting from the front of one of them was just catching the edge of the TV. x_x;

The discolouration did ultimately go away but it must've taken awhile because it was still present months later when I moved from Mom's to Dad's and was gone two years later when I moved back from Dad's to Mom's.

Well I'm stoked, turns out the bipolar electrolytic cap was the culprit after all.
After replacing the cap, the picture was distorted out the other way (barrel distortion) but the geometry controls in the service menu work now.
I spent the last hour or so with my SNES hooked up with an RGB-SCART lead, and tried to get everything as straight as I could.

At first the SCART input wouldn't work properly; the picture would roll diagonally. After switching channels and back to the SCART input it came good. Don't know what is happening there... but it's working now so I hope it stays that way!

Tomorrow I will put the plastic cover back on, and set up my room for a lazy day of gaming 😊

Excellent! Glad you got it working! Now time to enjoy some sweet RGB gaming goodness. 😁

Thanks so much for your help...I have set up in my computer room/manchild cave, in the cupboard so can be easily packed away 😁

Yes I know I need to tidy up the shelves.. .that's a job for another weekend

The TV is overall working pretty well. One thing I noticed is that horizontal lines seem to get slightly wider with brightness... i.e. brighter lines are wider. I used a test pattern to adjust the geometry, and I thought it was pretty straight, but when a lot of different colours are displayed, I can see the brighter colours are making the lines wider, particularly towards the right side of the screen.

This was most noticable in the amiga demo 'Copper Master' https://www.youtube.com/watch?v=5CUUOlYxlZ8 - if you look towards the right side of the box you could see the brighter lines made the side of the box wiggle left and right.

Is there some adjustment for this or is it mostly just due to age?

DonutKing wrote:

The TV is overall working pretty well. One thing I noticed is that horizontal lines seem to get slightly wider with brightness... i.e. brighter lines are wider. I used a test pattern to adjust the geometry, and I thought it was pretty straight, but when a lot of different colours are displayed, I can see the brighter colours are making the lines wider, particularly towards the right side of the screen.

This was most noticable in the amiga demo 'Copper Master' https://www.youtube.com/watch?v=5CUUOlYxlZ8 - if you look towards the right side of the box you could see the brighter lines made the side of the box wiggle left and right.

Is there some adjustment for this or is it mostly just due to age?

Some CRT monitors, even computer ones have that problem, where the bright lines are wider. Aida 64 for example has a monitor test, where it flashes a large rectangle of a white pattern on screen, and the sides of the screen are white lines, they move with the pulsing of the pattern on most monitors.

About to pickup this bad boy (lol are you my seller) how did you get into service menu and will I need a remote? Cheers