Sony Trinitron Picture Scrambled When Powered On

[scottradio]

I have a Sony KV-29XBR85 that has a scrambled picture when the set is powered on (audio works fine). It stays like that for 4-5 minutes before the picture straightens out. The scrambled picture is on all the inputs. Once the picture does come on it is steady and looks excellent. The TV initially had the green vertical bar problem so I disconnected the P-32 connector to disable picture in picture and it solved that issue. It's getting worse and the picture is taking longer to unscramble every time I power it on. I am wondering if this is being caused by a cold solder joint, bad cap or transistor and where in the circuit the problem is likely to be. Has anyone seen this issue before?

 

[starLED]

Here is the service manual.

 

[scottradio]

Thanks, I do have the service manual already and have been looking it over. I was hoping someone may have seen this problem before and may be able to tell me if it's likely a power supply issue, sweep circuit, crt failure or something else.

 

[crutschow]

Since it eventually runs okay, it could be a bad electrolytic capacitor somewhere in the power supply.
Can you monitor the power supply voltages as it warms up?

 

[drtechno]

Disconnecting the one connector just temporarily covered up the problem. The horizontal tearing is from the horizontal AFC circuit malfunctioning. Since the picture in picture is effected (first symptom) them then the AFC processor on the video Luma/chroma/sync processor (IC301) or an associated part is the issue or the first one I would start troubleshooting with the picture in picture connector plugged back in.

Since you have been having issues with service data, I'm going to share one of my copy that is more detail. Sony TVs are really picky on parts. So any semiconductor you replace, make sure that it is a sony part. Because it may not work correctly and sometimes weird things like controls going out of tolerance can even cause issues in them. Keep this in mind.

 

[scottradio]

OK, I will start by checking the power supply to see if there's any bad caps and then proceed to IC301 on the A board. Hopefully it's just a cold solder joint that can be easily fixed. I'll post an update when I can; thanks for the suggestions.

 

[Nigel Goodwin]

OK, I will start by checking the power supply to see if there's any bad caps and then proceed to IC301 on the A board. Hopefully it's just a cold solder joint that can be easily fixed. I'll post an update when I can; thanks for the suggestions.

Historically Sony TV's (at least in Europe) don't suffer from duff electrolytics in their PSU's, as they use decent quality ones - the issues lie with manufacturers (such as Samsung) using the cheapest lowest quality ones they can find, so failure rates are huge.

I'm suspicious about the 'green bar problem', and disconnecting P-32, you can't really tell from a picture, but it looks more a digital processing issue than anything else.

 

[drtechno]

I'm suspicious about the 'green bar problem', and disconnecting P-32, you can't really tell from a picture, but it looks more a digital processing issue than anything else.

This horizontal tearing until warmed up just makes me lead to the AFC circuit, but its also the same section is where picture in picture is combined. These later models incorporated it in an IC. I just can't remember if the factory repair kit for this problem included more than the ic301 because its been such a long time.

 

[camerart]

I have a Sony KV-29XBR85 that has a scrambled picture when the set is powered on (audio works fine). It stays like that for 4-5 minutes before the picture straightens out. The scrambled picture is on all the inputs. Once the picture does come on it is steady and looks excellent. The TV initially had the green vertical bar problem so I disconnected the P-32 connector to disable picture in picture and it solved that issue. It's getting worse and the picture is taking longer to unscramble every time I power it on. I am wondering if this is being caused by a cold solder joint, bad cap or transistor and where in the circuit the problem is likely to be. Has anyone seen this issue before?


View attachment 145253

Hi S,
I haven't had a new TV since the 80s, and the latest one is (was) a Sony Bravia, that packed in with a 1/2 screen last week.
I've just received a new modern TV, today, Much different.
I live in the south of the UK, if you want to old one
C

 

[Nigel Goodwin]

This horizontal tearing until warmed up just makes me lead to the AFC circuit, but its also the same section is where picture in picture is combined. These later models incorporated it in an IC. I just can't remember if the factory repair kit for this problem included more than the ic301 because its been such a long time.

As it's a non-EU model I've no experience with it, but I don't recall any factory repair kits for Sony TV's over here, other than the ones for the worldwide power switch issue.

I was chief engineer in a Sony Approved Service Dealer, and repaired thousands of Sony CRT TV's.

AFC is also only used for the main tuning, the 'similar' idea on the line sync was always called 'flywheel sync' from way back when it originally started. The Americans may call it something different though.

 

[starLED]

I was chief engineer in a Sony Approved Service Dealer, and repaired thousands of Sony CRT TV's.

I envy you, man. ​

 

[Nigel Goodwin]

I envy you, man. ​

Why? - it just means I'm old

 

[starLED]

Why? - it just means I'm old

I envy you on your knowledge and experience.

 

[drtechno]

AFC is also only used for the main tuning, the 'similar' idea on the line sync was always called 'flywheel sync' from way back when it originally started. The Americans may call it something different though.

we called that AGC for the the tuner section and the horizontal oscillator lock was called the horizontal AFC fly-back circuit or horizontal fly-back circuit. Vertical circuit was Vertical osc /Vertical AFC
Back in my TV days in Texas

BTW, there was a few acronyms and terminology for the same thing in electronics besides television. I think it was from bridging out electron theory from conventional theory.

 

[Nigel Goodwin]

we called that AGC for the the tuner section and the horizontal oscillator lock was called the horizontal AFC fly-back circuit or horizontal fly-back circuit. Vertical circuit was Vertical osc /Vertical AFC
Back in my TV days in Texas

No, AGC is Automatic Gain Control, and is applied across the IF and RF stages to deal with signal strength variations across a huge range (just as with a radio) - AFC is Automatic Frequency Control, and is applied to the tuner to keep it locked accurately on frequency. AFC is also usually used on VHF radios, for the same reason.

Fly Wheel Sync (developed on valve sets back in the 50's) isn't a 'frequency' control at all, if anything (although I've never seen it called that?) it would be Automatic Phase Control - it was (originally) a simple PLL system, and was used to help prevent 'tearing' on the picture under poor signal conditions. On a number of older sets it was available as a later upgrade, replacing the original simple line 'sync' circuit.

There was never any need to that on the vertical stages, so that was always a simple sync circuit.

Have a look here, flywheel sync starts on page 43, and goes into a lot of complicated detail and formulas , page 66 actually mentions Automatic Phase Control (so it was a good guess, as I've never heard it used before - but it's before my time!).

Television Receiver Design

BTW, there was a few acronyms and terminology for the same thing in electronics besides television. I think it was from bridging out electron theory from conventional theory.

Acronyms have become far too common, and all sorts of 'made up ones' seem to be appearing

 

[Inquisitive]

TMDA = Too Many Damn Acronyms

 

[scottradio]

An update: I thought I'd try going in the service menu to see if adjusting the settings would help. I noticed that changing the HFRE (h-freq) setting lessened the scrambling slightly but did not fix. I could see that there didn't seem to be any color or picture, just a black and white scrambled pattern. I also adjusted the AFC which straightened the green service menu text and numbers but did not affect the picture. None of the adjustments I made were written to memory, I left the settings as they were. I opened up the tv and after discharging CRT I took out the F (power) board. There is alot of brown gunk around the solder joints particularly around IC651, D659 and D657; see pictures. C664 also looked slightly bulged and leaky. I'm thinking the next step would be to recap the board and test the diodes.

 

[Nigel Goodwin]

'Recapping' is something you do on 70 year old valve equipment, not on a relatively modern TV from a manufacturer that has a reputation for using high quality electrolytics. If a capacitor IS actually domed, then it should be changed regardless - but you haven't posted a picture of it? - some types of capacitors do look slightly domed anyway.

I presume you have little test equipment?, and no experience repairing TVs?.

I opened up the tv and after discharging CRT

As that is a complete rookie thing to do - you've actually increased your chances of getting a shock from the CRT, when you had zero chance before, as you weren't working anywhere near it. Repairing around 30-50 TV's per week I'd probably only discharge the CRT on one or two per month, if that. You should also be aware, if you're concerned about the CRT?, that once you've discharged it, it will almost certainly charge back up to a certain extent.

So presumably you don't have an ESR meter? (essential for testing electrolytic capacitors), or an oscilloscope which can do the same, but with the set powered up. If you do have a scope, then C664 can easily be checked by clipping the scope on R619 (easy point to clip the scope probe on), and checking how much ripple there is (there should be VERY little).

As it's a thermally intermittent fault, a can of freezer spray may help you locate the fault? - wait until the set has started working OK, then spray the various PCB's in turn, seeing if you can find aboard that when cooled reintroduces the fault.

 

[drtechno]

No, AGC is Automatic Gain Control, and is applied across the IF and RF stages to deal with signal strength variations across a huge range (just as with a radio) - AFC is Automatic Frequency Control, and is applied to the tuner to keep it locked accurately on frequency. AFC is also usually used on VHF radios, for the same reason.

I know what AFC and AGC is. The AFC in the tuner is internal. The horizontal and vertical have their own but they are keyed or controlled by the incoming video synchronization pulses plus a closed loop frequency adjustment.

There is alot of brown gunk around the solder joints particularly around IC651, D659 and D657; see pictures. C664 also looked slightly bulged and leaky. I'm thinking the next step would be to recap the board and test the diodes.

It looks like someone didn't clean their flux when they solder last time. But since there isn't a hard failure, I would replace caps that are bulging , re-touchup any crystilized/cold solder joints, clean up the board and observe any changes.

Just for you to know, a capacitor rarely causes issues by itself and usually a cap failing is for some other reason. That is why recapping a tv set is more of a use case than a common practice.

 

[drtechno]

Acronyms have become far too common, and all sorts of 'made up ones' seem to be appearing

I think there is more names to the same thing than acronyms. flyback diode, horizontal output diode, dampener diode, flywheel diode. counter emf diode, how many names do we need to have for the same diode?