Toshiba 32AV502R power supply restarts continuously


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Toshiba 32AV502R power supply restarts continuously

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jamanota
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Sep 20, 2010, 11:26 PM

Post #1 of 10 (12199 views)
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Toshiba 32AV502R power supply restarts continuously	Can't Post

Just over 1 year old Toshiba 32AV502R, after a few minutes of use the power supply shuts down and starts up again for a few minutes or even a few seconds. I already narrowed the problem down to the +5 Volt part of the SMPS. A load of more than 500 mA will bring the power down, TV needs about 700 mA to work. I can reproduce the problem with a dummy load (7 ohm). I don't have the schematics of the TV or the power supply, but the +5 Volt regulator is a VIPER27L . Any help is appreciated as I am running out of ideas. Problem is relatively easy to reproduce but is somewhat random and dependent on temperature. <br>

(This post was edited by jamanota on Sep 21, 2010, 12:01 AM)

jts1957
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Sep 20, 2010, 11:33 PM

Post #2 of 10 (12190 views)
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Re: [jamanota] Toshiba 32AV502R power supply recycles itself [In reply to]	Can't Post

Lytics?

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Location: Far, Far Away

jamanota
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Sep 21, 2010, 12:21 AM

Post #3 of 10 (12184 views)
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Re: [jts1957] Toshiba 32AV502R power supply recycles itself [In reply to]	Can't Post

The two capacitors look OK, no bulging. I applied an external 5 V DC to the filter and loaded the output with 5 ohm, output was a stable 5V.

jts1957
Veteran

Sep 21, 2010, 2:10 AM

Post #4 of 10 (12182 views)
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Re: [jamanota] Toshiba 32AV502R power supply recycles itself [In reply to]	Can't Post

Lytics= "LOOK" good. How do they test? Or quicker yet - swap 'em (if you got 'em).

Capacitor failures include:
1) Change in value
2) Equivalent Series Resistance (ESR)
3) Dielectric Leakage
4) Dielectric Absorption

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Location: Far, Far Away

jamanota
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Nov 3, 2010, 9:42 PM

Post #5 of 10 (12097 views)
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Re: [jts1957] Toshiba 32AV502R power supply recycles itself [In reply to]	Can't Post

Capacitors were swapped for new ones, no improvement unfortunately.

Ron.M
Veteran

Nov 3, 2010, 10:46 PM

Post #6 of 10 (12090 views)
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Re: [jamanota] Toshiba 32AV502R power supply restarts continuously [In reply to]	Can't Post

jamanota;....

I am soooo outta my league here...
But , I thought I'd give this a shot since it appears to be a power supply problem...

I "Googled" VIPER27L

& got this;=>...

http://media.digikey.com/...s%20PDFS/Viper27.pdf

& this;=>...

http://www.21dianyuan.com/...881499e1d01bd328.pdf

(Has sample schematic) ^^^

Since you appear to be dealing with an IC instead of an older conventional 3 pin 5 volt regulator IC , then your choices appear to be somewhat limited...
You can try to replace the IC , troubleshoot the circuit (Possibly using the one in the link as a guide ??) OR replace the power supply board...

BTW;...
When you use your external 5 volt supply , do you have the same problem ???
Does the set come on & STAY on ????

You may also want to consider investing in a can of electronic "freeze"....

Good luck....

Later....Ron.M.... Cool

....
Veteran & Retired TV technician

jamanota
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Dec 8, 2010, 2:45 AM

Post #7 of 10 (11976 views)
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Re: [Ron.M] Toshiba 32AV502R power supply restarts continuously [In reply to]	Can't Post

Still have not found the problem in the 5V circuit.

I am now thinking about replacing the whole 5V circuit with a small separate powersupply and leave the 12V and 24V as they are.

However when I do this the TV ( processor ) doesn't seem to start up, I see no picture and hear no sound. The replacement supply is 7805 based and can handle the load.

I can think of two causes for the processor not starting,

1. Original power supply has a soft start, the 7805 not
2. I need to give some kind of power OK signal to the processorboard

Can someone advise me ?

Four extra wires go from the powersupply to the main board and they are marked: #POWER , #ACD, #INV, and #DIM. The last two running thru to the Inverterboard. The #POWER switches the 12V and 24V on and off.

darstr
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Dec 8, 2010, 10:12 PM

Post #8 of 10 (11969 views)
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Re: [jamanota] Toshiba 32AV502R power supply restarts continuously [In reply to]	Can't Post

In Reply To

Four extra wires go from the powersupply to the main board and they are marked: #POWER , #ACD, #INV, and #DIM. The last two running thru to the Inverterboard. The #POWER switches the 12V and 24V on and off.

Power is your power on command from the main board
ACD is your AC detect. The main board detects that AC was supplied then sends the Power on command to the power supply
INV is your inverter on command from the main board. Once main board is fully running it sends the command to the power supply to turn on your backlights
Dim is commonly known as PDim. That is the main board controling how bright your backlights get. There is a lot of handshaking that is taking place. Would strongly advise against using a seperate power source. Switch Mode Power Supplies are not very expensive. Good luck to you.

jamanota
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Dec 9, 2010, 1:35 PM

Post #9 of 10 (11962 views)
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Re: [darstr] Toshiba 32AV502R power supply restarts continuously [In reply to]	Can't Post

Thanks darstr, unfortunately I don't live in the US so a replacement powersupply would cost me more than $100. That's to expensive for a $350 TV set. I rather spend some more time investigating what's wrong. I did however find a schematic last night for the 32AV502U which should be very much the same as my 32AV502R. That will make troubleshooting easier for me.

A question about the ACD signal, if there is no AC then the whole powersupply doesn' work. Is this meant as a signal to gracefully shut down or something, when power goes down. I can't see any other sense for this.

darstr
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Dec 9, 2010, 1:44 PM

Post #10 of 10 (11961 views)
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Re: [jamanota] Toshiba 32AV502R power supply restarts continuously [In reply to]	Can't Post

All it is is low DC voltage that lets the main board know it is ok to turn on the set.

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