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Old Sanyo TV Model CEP2034

dark666

New Member
Hi.

I'm repairing an old Sanyo TV for a friend.
The TV wont turn on.
My friend told me that one he turned on the TV and heard a small click sound and the TV never worked.
I openned the TV noticed some broken solder joints, I resoldered every broken joint in the circuit.
Now this is what happens, I turn on the TV, the led doesn't come up and I hear a loud and irritating "skwiking" sound coming from the PSU area!

I tested, resistors, diodes and zenners on that area all appear OK.

It appears that the sound is comming from one of the transformers!

What you guys think?

Thanks
 

btcg

New Member
Hi.

I'm repairing an old Sanyo TV for a friend.
The TV wont turn on.
My friend told me that one he turned on the TV and heard a small click sound and the TV never worked.
I openned the TV noticed some broken solder joints, I resoldered every broken joint in the circuit.
Now this is what happens, I turn on the TV, the led doesn't come up and I hear a loud and irritating "skwiking" sound coming from the PSU area!

I tested, resistors, diodes and zenners on that area all appear OK.

It appears that the sound is comming from one of the transformers!

What you guys think?

Thanks

Look closely at the flyback transformer. See any cracks?

Put your DVM in the diode testing position, and (with the unit unplugged) read between the emitter and collector of the horizontal output transistor.
Is it shorted? If so, unsolder the emitter lead and test it again.

You can get fooled into thinking it's a power supply problem when it's actually in the horizontal secondary.

When you resoldered, you may have restored a startup voltage, and now it's going into shut-down. That could be why the LED isn't lighting now.

Switched mode supplies usually will create a voltage to "start" the horizontal sweep circuit, thus energizing the flyback. Once the flyback is going, secondary windings provide a feedback voltage to the power supply, as well as powering other circuits. These secondary windings off the flyback will have a low value resistor and diode off of them. Check these. You can physically follow the foil pattern off the flyback and quickly locate and check these.
 
Last edited:

dark666

New Member
Hi.

There is no power getting to the flyback transformer!
The power stops somewhere near the PSU.
There are a couple of resistors right after the PSU that have no power at all.
Like I said the loud beeping comes from the PSU, a friend of mine told me it could be the PSU coils and transformers.

What you think?

Thanks
 
Last edited:

dark666

New Member
I was thinking, if the problem is in the flyback wouldn't the TV stay in standby with the red led on?
Because it doesn't even do that!
 

btcg

New Member
I was thinking, if the problem is in the flyback wouldn't the TV stay in standby with the red led on?
Because it doesn't even do that!
The direct answer to that question is, under some circumstances, yes.
For instance, if it were going into shutdown.

But as an old-time tech once observed:

"You can't shutdown something that never gets started"

If you checked the horizontal output transistor (espectally e-c) and it's not shorted, and you have have no collector voltage(sometimes you have to unsolder the collector and read the circuit voltage), you most likely have a power supply problem. Check things there.

The transformer in the power supply? Most likely, no.

Keep in mind what a switched mode power supply is doing:

You are simulating A.C. in the psu transformer by turning the transistor/output device on & off very fast, thus creating secondary voltages that start the set.

Consider, if you "float" the collector of the horizontal output transistor, and you read a dc voltage of 150v or more, check the emitter circuit of the horizontal output transistor. You may have a small resistor between the emitter and the circuit ground that's open.

No luck with any of this: invest in a schematic.
 

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