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]

How many names do we need to have for the same diode?

How many Americans are there?

 

[drtechno]

How many Americans are there?

Its not an american thing either. Has to be the stupid British.

 

[starLED]

Its not an american thing either. Has to be the stupid British.

I think the Americans are more prone to using acronyms, at least in the movies.
It's not so common in the Europe though.

 

[Nigel Goodwin]

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.

Apparently not

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.

Complete and utter nonsense - the reason electrolytic capacitors fail (which is by FAR the most common failure in electronics) is the use of sub-standard capacitors during manufacture to reduce costs. For example, the electrolytic capacitors Samsung used in the Sky+HD boxes they built for Thomson, and in their TV's of the same period, had a design life of only 9 months at the temperature they were run at. Needless to say, failure rates were huge, and while still under warranty their TV's no longer had spares available.

Incidentally, I see nothing wrong with the bottom of the PCB above, the excess flux around larger items is quite normal for boards from that period, and of no consequence.

 

[starLED]

Complete and utter nonsense - the reason electrolytic capacitors fail (which is by FAR the most common failure in electronics) is the use of sub-standard capacitors during manufacture to reduce costs.

How much do they actually save on those sub-standard caps per TV?
Or is it a business trick to make people buy new ones?

 

[Nigel Goodwin]

How much do they actually save on those sub-standard caps per TV?

It's a desperate rush to make the sets as cheap as possible, and I presume those appalling quality capacitors were a small fraction of the price of decent quality ones.

In a similar vein, a few years back LG (another 'cheap as possible' Korean manufacturer) brought out a new lower cost LCD panel - this was achieved by drastically reducing the number of back light LED's, and over driving the ones that were left. This obviously drastically reduced the life span of the panels, to again barely exceeding the one year warranty. Basically the LED's massively over heat, the diffuser lens fall off and rattle round the bottom of the panel, and the LED's change colour - heading towards the actual Ultraviolet they actually generate.

Even worse, LG sold the panels to various other manufacturers, including Samsung, so the problem is prevalent across many brands.

Funnily enough, last Sunday I was in Cambridge, and went to KFC for lunch - they had a row of four LG screens displaying the menu - I've attached a picture of the left hand one below. The right hand one was also duff, but not as badly as the picture below, the middle two were OK. You can clearly see where the diffusers have dropped off, and the LED's are shining brightly through the panel - but if you look closely, the other diffusers have fallen off as well, but the LED's are totally fried, and have gone towards UV.

Or is it a business trick to make people buy new ones?

As the TV sets were failing under warranty in huge numbers it was obviously costing Samsung a LOT of money for warranty repairs. Even if the set didn't die until after the warranty, customers are unlikely to ever buy Samsung again - so it's pretty counter productive.

 

[drtechno]

Apparently not



Complete and utter nonsense - the reason electrolytic capacitors fail (which is by FAR the most common failure in electronics) is the use of sub-standard capacitors during manufacture to reduce costs. For example, the electrolytic capacitors Samsung used in the Sky+HD boxes they built for Thomson, and in their TV's of the same period, had a design life of only 9 months at the temperature they were run at. Needless to say, failure rates were huge, and while still under warranty their TV's no longer had spares available.

Incidentally, I see nothing wrong with the bottom of the PCB above, the excess flux around larger items is quite normal for boards from that period, and of no consequence.

apparently not yourself

Most cap failures in CRT TV sets were caused by brilliant engineers laying out their circuit board so that electrolytic capacitors get cooked by high wattage resistors.

 

[drtechno]

Complete and utter nonsense

I find you to be complete nonsense, wannabe know-it- all

 

[scottradio]

I misspoke/misswrote when I said I would recap the board.. I meant I will replace any faulty caps as there's no sense in replacing good caps and I don't want to do any unnecessary or sloppy work on this TV. I've worked for years on older valve/tube radios and audio equipment but am new to working on a Sony trinitron so this is a step up in complexity. I'm enjoying learning more about these televisions and the comments I've read here. I've thought about getting an esr meter in the past and have decided to order one since starting this.

 

[drtechno]

I misspoke/misswrote when I said I would recap the board.. I meant I will replace any faulty caps as there's no sense in replacing good caps and I don't want to do any unnecessary or sloppy work on this TV. I've worked for years on older valve/tube radios and audio equipment but am new to working on a Sony trinitron so this is a step up in complexity. I'm enjoying learning more about these televisions and the comments I've read here. I've thought about getting an esr meter in the past and have decided to order one since starting this.

Since its a thermal symptom, maybe using an IR thermometer or a thermal camera and look at what part is heating up. Most likely its the video IC since another circuit (picture in picture) is failing.

 

[Nigel Goodwin]

I find you to be complete nonsense, wannabe know-it- all

Hardly a 'wannabe', as a multi-award winning service engineer with 46 years in the TV servicing trade - something you're obviously not in, or have little experience in, if you don't know the absolute basics.

 

[starLED]

Hardly a 'wannabe', as a multi-award winning service engineer with 46 years in the TV servicing trade - something you're obviously not in, or have little experience in, if you don't know the absolute basics.

Is this a USA vs UK thing?
I thought you guys like each other.

 

[rjenkinsgb]

Most cap failures in CRT TV sets were caused by brilliant engineers laying out their circuit board so that electrolytic capacitors get cooked by high wattage resistors.

Apparently you have never looked at the data for generic electrolytic capacitors???

The large majority have a rated lifetime of between 1000 to 5000 hours, when used at their full rated temperature, ripple current and voltage etc.

That's around 40 to 200 DAYS.

There are formula to calculate how much longer the lifetime will be if each rating is under-run; eg using [more expensive] components with higher temperature, higher voltage and higher maximum temperature ratings.

Any lifetime is possible - tens of millions of hours if you wish - but the higher rated parts cost more and are generally larger!

So, makers of mass produced consumer products very often cut the extra cost to the minimum they think they can get away with, for any given product.

(And similar things apply to other components running excessively hot, just not to the same orders of magnitude).

 

[starLED]

Apparently you have never looked at the data for generic electrolytic capacitors???

The large majority have a rated lifetime of between 1000 to 5000 hours, when used at their full rated temperature, ripple current and voltage etc.

That's around 40 to 200 DAYS.

You are assuming full workload 24 hours/day.

Estimates suggest that in 2024 U.S. adults will spend an average of nearly three hours watching traditional TV each day.

In my country legal warranty needs to be 2 years minimum for tech devices.
Then those caps have to withstand 1.3 to 6.8 hours per day if 1000 to 5000 hours caps lifetime.

For average use, that will be close, but it's possible.

 

[drtechno]

Apparently you have never looked at the data for generic electrolytic capacitors???

Apparently you never really worked on a TV set. You troubleshoot what is wrong, not arbitrarily change parts.
That is why they should plug back in the picture and picture insert and troubleshoot it with the hard failure because its associated. The IC's voltages will reveal the problem of where its going wrong and they are still available if there are faulty.

 

[scottradio]

Hello, I was able to repair the tv and it is working perfectly now. It turned out that C664 on the power board was the culprit, all other components tested OK. I replaced it and that cleared up both the green vertical bar problem (p-32 is connected again) as well as the scrambled picture on startup. I'm so glad to have this set up and running again, thanks

 

[starLED]

Great!
I am glad you saved your TV.

Nigel was right about the cap failure (post #24).

How exactly did you find the C664 was the issue?

 

[scottradio]

I tested all the power board caps but I could see that C664 was slightly bulging and I used my esr meter to confirm it was bad. I also could see when I removed it that it had leaked on the board. I'm relieved it was a simple fix, I think it's a great looking TV so I really wanted it working again. I think crutschow in post 4 was the first to suggest it was a power supply issue; I do appreciate all the helpful comments from those who posted and tried to help out.