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TV powers down

First TV would not come on and I found power supply PW8552 had vented electrolytic caps C840 and C841, R820 burned open in darkened area of PCB, and blown F807.

I found suggestion to replace caps C840, C841, C822, R820, Q840 (L787MR05) and Q802 (STR-D1005), all in darkened area of PCB to fix symptom of TV would not come on.

Now TV comes on but powers off after 5 or so minutes. It will come back on when I pull the plug and reinsert it.

Any ideas where to check next? I know this is an old TV, but I have come so close, I just want to finish fixing this problem.

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  • Larry Copley Jan 26, 2008

    Sorry, my first post, and I thought I filled in somewhere that this is a Toshiba rear projection model TP5288 with Toshiba Chassis TAC8891 (shared by 46 inch model TP4688) and the Power Supply board is PW8552 which is the board the component references are from.

  • Larry Copley Jan 27, 2008

    After replacing Q802 and Q840 (I think these were the regulators because they each had five pins) The relay clicks on and the TV comes on right away, and works great for about five minutes. Then the relay clicks off. It comes back on again without using the power button by power cycling the plug i. e. I un plug the set and then plug it back in and it comes on by itself.

    I read somewhere there are Chemical Fuses on the board and I was kinda thinking maybe the Chemical Fuses reset themselves when I cycle the power.



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What is the make and model number of the set your trying to repair? Post that information and I will be able to possibly help you out.

Posted on Jan 25, 2008

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  • Sonny Berry
    Sonny Berry Jan 26, 2008

    When you power up your set whart does t do?

    Do you hear the relay click? Have you checked the voltage regulators all of them? Usually in sets that have that many shorted components I always check all regulators as well as check for shorted line coils and leaky diodes in the Bridge rectifier.

  • Sonny Berry
    Sonny Berry Jan 26, 2008

    Also if you dont have any success you may want to call PTS they usually stock all the modules for thousands of models at about 30 percent of what the OEM prices here is a link.

  • Sonny Berry
    Sonny Berry Jan 27, 2008

    Yo have a resistor or diode that must be open. Check near the regulators that you replaced. What is happening is the resistor is probaly allowing a rise in voltage and thats tripping the shutdown mode if it cycles off fast enough your set can power back on when you replug it. I am not famillar with chemical fuses. However toshiba does use fusible resistor FR and variable resistorsVR. I will do some research on that chassis. Check the resistors near those regulators take one lead out of circuit to check them.



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1 Answer

The power button is broken how to turn ontv

Hello Andrew

You didn't specify what you mean by "Broken"

Do you mean physically broken or
It just doesn't turn the tv on?
There are separate answers for each.

1:To fix a physically broken switch you could simply open the TV up and attach 2 wires to where the switch contacts are soldered to the PCB.
Run the wires to a new switch. Probably a NO (Normally Open) type. A Round switch could be mounted easily with a drill hole through an unused area of the case. Pressing a NO switch closes the contacts momentarily to trigger the digital turn On.

2:You could remove the old switch & attempt to get an actual replacement or a similar mountable switch from a components supplier.

3:If the switch is actually physically OK and the internal contacts are working (test with multimeter) then the problem is with the digital switch mode power supply that supplies power to the main circuits.

This would probably be caused by leaky Electrolytic Capacitors on the power supply PCB.
In that case, if your up to using a soldering iron and locating the Cap's then this would be an inexpensive way to fix the TV.

Good Luck
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Hi Beluda

Modern Digital TV's are really just Digital Computers with a CPU & Memory & a Flat Screen digital monitor, which uses the internal computers video memory to display content.
Streaks therefor would indicate a bad ribbon cable from main pcb to flat screen video screen or a video memory problem.

Today's HD TV's are NOT like the TV's of the past (Analog) that could easily be tweaked & fiddled with to get better picture results. It is made with Solid State Digital computer components.
So.... with that in mind.
Do you have the technical ability to fix a computer's internal cpu board?

If so, Open it up and put on your anti static strap & lets go.

Disconnect The Power.
Switch off at the wall to retain an antistatic ground point.
If you have a 3 pin power outlet (ground pin)

Check internally for poor connections (cold solder) or loose ribbon cables & connectors?
Look for cockroach & insect bodies & droppings on the circuit boards. (Shorts)
Look for overheated or damaged components.

But.... the biggest & most likely problem is that the DC voltages are not stable. (Poor Filtering)
This is caused by Leaky or Bulging Electrolytic Capacitors.
They have internal chemicals that deteriorate over time. Especially by being too close to their max voltage rating (printed on side)

There are No Internal 25KV voltages to worry about on Digital Flatscreen's.
There is a shock hazard on AC side of Switchmode Board.
Electro Caps on AC Input side can hold 110 / 240v
Check the Switchmode internal power supply on DC Side for bad Electrolytic Type Capacitors.
The insulated Tin Cans on the PCB with a Negative stripe down one side
Bulging or leaky Electrolytic Caps cause many failures in modern digital TV's

If you are not a Tech Type....
Take it to a service tech & ask to check Electrolytic Caps.
Most Tech's these days will Just Do A Board Swap. Costing $$$
If you are a tech type and feel like exploring & possibly fixing the problem.

Good Luck
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1 Answer

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Hi Gertha
Switch Mode Power Supply.

Either a PCB or a Metal Box. Usually the first place the AC wires go to internally. They fail usually because of Bad Electrolytic Capacitors. Look at the Electrolytic "Tin Can" Caps and see if they Bulge from the top or are leaking on top or bottom,
Replacing these with similar or better values does the trick.
Otherwise replace the whole Power Supply PCB Unit.

Good Luck

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first place to begin is if able test voltages in and out of the power board inside the set---if not able to do that consider having a shop look at it.

If you get it open:



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What will be the problem when it is not showing power

No power is a typical failure of the switchmode power supply, which, unless you have sufficient knowledge of this circuit, requires a workshop service centre repair. Several components, including the most likely culprits (electrolytic capacitors) will need replacing. In extreme cases, the entire PCB will need to be replaced.

Bad caps are usually very easy to spot in most power supplies, look for crooked, swollen or bulging caps, and/or splits in their vents (the impressions in the tops of them) along with electrolyte spilling out (electrolyte is highly corrosive, so if any has leaked out of any caps onto the PCB, it may damage the copper tracks). Some may have dropped in value, some may be open-circuit (no capacitance at all), while others may have taken out one or more IC regulator and/or the chopper transistor(s); this could lead to an expensive repair, particularly if surface-mounted components on the copper side of the board are short-circuited.

NOTE: when servicing switchmode power supplies, with electrolytic capacitors, it is standard practice to replace ALL the caps in this circuit to ensure reliability and to minimise the likelihood of a service recall later - even if the ESR of some caps measures OK, they should still be replaced, and in a lot of cases, the working voltages and values of those capacitors which are replaced may be uprated/increased.

As I said, unless you have knowledge (and experience) with this type of circuit, submit your unit to an authorised repair centre, get a quote on the likely repair cost(s) and/or a second opinion from an authorised technician as to the extent of the fault(s) in your unit, then make a firm decision afterwards as to what you want to do about it.

It's up to you - either spend a fortune in repairs to this one, or, if it is NOT a DVD recorder, buy a new player - but only as a last resort. I suggest that you get the repair quote first before going any further.

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1 Answer

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Well-designed switchers are wonderfully efficient and very reliable if the maker didn't cheat on component quality. I've repaired literally thousands as a sideline in a now retired business and after studying them and adding a ceramic cap.or two and better quality electrolytics, they will run for decades. At one time, I had standard repair prices on ~ 70 different models.
My guarantee was 'lifetime' and that was limited only because I retired.

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Good Day;
Try these first. This TV is an oldie 1988?


Good Luck, big IRISH.

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