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Old 11th Aug 2020, 3:40 pm   #1
PhilipTusar
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Question Sony Trinitron KV-1400UB

Hi there,

I am new to working on Sony TVs.

I have acquired the KV-1400UB from someone who claimed that it used to work prior to transporting. It seems to be one of the first monitor style portable Trinitrons with the touch sensor channel buttons.

What it does now is make a buzzing noise similar to an alarm panel, or one of those aerosol bike horns but very quiet.

It appears to be coming from the main board, PSU section. Possibly a protection circuit in action.

Now if it is true that it did work before moving it, then what possibly could have been disturbed during transportation to upset the PSU so much? I see a crack on the case but no breakages inside could be noted yet and all plugs seem to be fully seated.

I could find no (free) service manual to check before spending any time or money on this.

Anybody out there come across this buzzing issue on an early Trinitron yet?
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Old 11th Aug 2020, 5:40 pm   #2
simpsons
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Default Re: Sony Trinitron KV-1400UB

What makes of TV's are you used to working on? A noise is a noise. Is this with or without the Sony in good working order.

I would deal with it in the well known way, narrow down where the sound is coming from and use a spoon, not wooden, or similar to act as a trumpet.

The schematic for this and other Sony's is freely available on this site and elsewhere.

Keep the forum posted with the cause.

Good luck

Chris
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Old 11th Aug 2020, 5:51 pm   #3
PhilipTusar
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Default Re: Sony Trinitron KV-1400UB

I may not have been clear in my description.

The set does not work - no picture or sound, and emits that noise from the PSU board.
It suggests to me a PSU failure, bad caps or short somewhere.

I was hoping that someone may have had a similar fault to compare notes, so as to help narrow it down a bit.
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Old 12th Aug 2020, 10:23 pm   #4
simpsons
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Default Re: Sony Trinitron KV-1400UB

Screeching from the power supply suggests a short circuit or high current drain on the regulated output.

The Sony power supply follows their usual practise with over current and voltage protection as described in Practical Television but the circuit has been designed with certain faults in mind . As with all switch mode supplies, you will need to use a 100 watt 240 lamp as load should you disconnect the LOPT horizontal output transistor supply to eliminate this part of the circuit

From the circuit available on this and other sites, L603/c621 is the regulated output and from memory, the plug and socket connections to the different boards will allow you to narrow down the problem.

You say that the cabinet is cracked and it may be that a track on the pc has been compromised so removing the horizontal drive and so I would start looking there.

Chris
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Old 12th Aug 2020, 10:58 pm   #5
slidertogrid
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Default Re: Sony Trinitron KV-1400UB

If you suspect the set has been dropped the first thing I would check is for arcing in the tube neck if the tube is damaged and the vacuum is gone you will get sparking in the gun with a buzzing noise. sometimes if the tube is damaged it is just the small evacuation pip which is broken and it's not that easy to see without removing the base panel.
Otherwise check for cracks in the panel around larger parts, the Line output transformer would be a good place to start check for cracked tracks around the pins.
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Old 13th Aug 2020, 10:25 pm   #6
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Default Re: Sony Trinitron KV-1400UB

In my experience the first thing to break in a fall is the circuit board around the LOPT. (or ather heavy components) Sometimes the cracks were hard to spot as they were so narrow.
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Old 3rd Sep 2020, 11:42 am   #7
PhilipTusar
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Thumbs up Re: Sony Trinitron KV-1400UB

Hi All,

Just to let you know that I have solved the issue.
It was a bad connection of the Collector on the Line Output Transistor.
Tracing the 105v from the C pin on the Line output transformer, I got a good voltage all the way to both yoke sockets, then 0.7v at the Collector on the transistor. I could see no breaks in the pcb track and reflowed the solder joint to no evail. I then bridged the track with a wire, then got the correct voltage and a working TV.
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