vertical output stage

Can we assume you were not trying to operate the tv set when it supposedly failed? The tv would had to have been turned on for a vertical circuit failure as the voltages to it would normally be off when the tv is off.

Assuming that the vertical deflection is the only failure in the set, it is way too far removed from the power supply to have failed from a brown out.

Ac line - Main tv power supply regulator - Deflection/HV circuit - Flyback derived secodary voltages - vertical circuit.

You should be able to see why if there was zero damage along the way that the vertical circuit could not have been caused from a simple brown out condition. If the tv has a typical SMPS power supply, then it would have been able to operate normally with the ac line voltage all the way down to 90 volts ac with no damage.

I agree with David, it's too far removed from the AC line to have been caused by a brownout. I have customers try to get me to write failures due to outside influences, and I won't unless it's even remotely possible, and then I write it up as a potential power related issue. Items that are clearly damaged are written up that way.

Understand that if the power company or insurance company audits the repairer's claim and finds fraud, this will be a very serious problem for him and he might lose his license.

John

the TV set was off but it would have been on what I beleive is standby as we turn our TV off with the remote. So why would the TV have gone bang during the brownout. Working the evening before then not working when I turned it on after the power was corrected?

Electronics fail. You might want to post the make, model, and age of the tv set. If the tv was more than a couple of years old, it was probably just a coincidental failure when the tv was turned on.

Most electronics fail at turn on when it is a random semiconductor failure.

Other things like weak capacitors in the vertical circuit that were neglected to be repaired when the image first started to change will generally cause a run time failure. Happens in the middle of the set running. Other components like coils, transformers, etc also can fail in this way.

The TV was a Digitor brand 18 months old. I know its a cheaper brand but am amazed at the coincidence of this happening when the TV was off and during a brownout.

Since the shop probably has the service manual and everything they need, have them map out where the parts are that failed and needed replaced.

Has the tv been repaired yet? If it has why not post exactly what components were replaced and ask the shop to let you know where those components land in regards to potential ac line power problems.

Equipment very often fails when turned on, that's just the way it goes. It likely had a problem developing and that last thermal cycle exposed it, would have failed soon anyway.

I'm not sure why it's amazing that a cheap crappy TV failed, if it was off then the vertical chip was not recieving power anyway so it doesn't matter if there's a brownout.

It seems what you are saying is that this problem has occured not during the brownout but when I turned the TV on. I accept this as you guys are the experts and I appreciate all your help so far to help me understand what happened. So why would the TV have gone bang and smell of a burning smell whilst it was switched off.

I didn't catch that part, what parts went bang? Was that the vertical chip??

Don't take this the wrong way, but these TVs are built to last the warranty period. Anything more is considered "bonus time". During the warranty period on most brands like this, the distributor will replace the TV (and consign it to recycling or a landfill). Once out of warranty, they are considered to be a disposable product with no service or parts available.

John

Most likely something in the standby power supply. It is on all the time (whenever the TV is connected to the AC line) Otherwise you couldn't use the remote control.

I've seen one model (forgot which) a year or so ago, that took the vertical voltage from the power supply instead of the flyback.

I would still have the servicer that has the tv set right now complete the repair and provide you with the bad parts and give you a map similar to what I posted so you can see exactly where the parts were that failed.

Once you find out where the parts that failed were in relation to the ac mains power source, then you can make an intelligent decision as to whether it could have been related to the brown out.

The servicer might not have found all the bad parts, but only the obvious ones so far and needs to complete the repair at hand to determine if there is another problem.