46" LXI/Magnavox Power Supply Problem


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46" LXI/Magnavox Power Supply Problem

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esemilio
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Jan 11, 2013, 7:05 AM

Post #1 of 13 (3131 views)
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46" LXI/Magnavox Power Supply Problem	Can't Post

I have an older (1988) LXI 46" PTV 325 chassis; with apw009 power module. After 5-15 min of operation the picture flickers, looses color, & shrinks slightly, & volume goes down. Sometimes it will correct itself, other times (but not all the times) the problems gets corrected momentarily if unit is turned off and back on. When I monitored the 200V I get an initial reading of 177V & when it starts flickering the voltage drops gradually to 150V and then stays steady.
I have checked solder joints on both the deflection and power board, changed a couple of electrolytics (the 100uf 200volt cap in the power supply) none visually showed any signs of problems, it did not solve the problem. This set has not been used much (coolant had been replaced) so it still gave an excellent picture so I want to fix it if I can. Any suggestions on trouble shootin/fixing it would be greatly appreciated!
Emilio

Ron.M
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Jan 12, 2013, 12:43 AM

Post #2 of 13 (3122 views)
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Re: [esemilio] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

esemilio;.....

I have the DPTV325 Service manual & it doesn't show a 46" model...
It has a 43" & 55" model...
Also , the manual was printed in 2002....
Care to esplain the discrepancy ???

Quote

When I monitored the 200V I get an initial reading of 177V & when it starts flickering the voltage drops gradually to 150V and then stays steady.

Where did you read the "200" volts at ???
When it stays steady , is the pix & sound OK ???
Meaning "normal" ???

How much electronic/TV repair background experience do you have ????

Can you take & post pix IF needed ???

Thanks....

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

...
Veteran & Retired TV technician

esemilio
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Jan 12, 2013, 3:26 AM

Post #3 of 13 (3116 views)
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Re: [Ron.M] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

Ron.M,
1) Thanks for responding.
2) It is a LXI model 626.54461850. (Assembled July 1988).
3) A block wiring diagram with the set shows a "APW009 power panel", "AIO338 deflection module" & all the other modules. I monitored the voltage on the J107 connector on the power module - on the wiring block diagram it is marked +200V ETH REF. The voltage stays steady at 177-176 and I have a stable good picture and sound; 5-15 minutes later the voltage starts drifting lower - the picture flickers - sometime it "recovers" most of the times picture gets worse - lose color, gets a little smaller, sound goes down. IT is not watchable. Turn set off and, 1-2 sec later, back on picture and sound sometimes recovers sometimes not. If I wait a little longer in come on OK for another 5-10 minutes.
4) I have some basic electronic experience -can solder, know about cap & resistors, basic electronic circuits, & understand danger of high voltage; I have replaced the HOT on both modules 6-8 years ago.
5) I have resoldered many spots on the deflection and power panels looking for a cold solder spot, replaced the 100mfd 200V cap on the power panel mentioned in some of the posting I reviewed-I have been shooting in the dark because the panels are interconnected it has been hard for me to diagnose.
6) I can take pictures

(This post was edited by esemilio on Jan 12, 2013, 3:29 AM)

Ron.M
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Jan 12, 2013, 7:40 PM

Post #4 of 13 (3105 views)
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Re: [esemilio] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

esemilio;....

OK , we live & we learn...
I have the "DPTV325" & lo & behold , it is not the same as "PTV325"....
Leave it to Sears to make things miserable for any service tech...

I DO have the PTV325 service manual...
The voltage you are reading at J107 may/may not be helping & could be misleading us....
Check the voltage at J108 pins 6 &/or 7 for 130 vdc...
Use pins 1 &/or 2 for your "-" or ground connection...
Monitor that voltage for changes when the set craps out...
Be advised that this chassis has many possibilites for that problem...
Those 2 boards (APW009 & the deflection panel to the left) work together & if one blows the HOT , BOTH boards WILL have fried transistors...
So we could be fighting a losing battle..
Please post results...

Later...Ron.M... Cool

...
Veteran & Retired TV technician

esemilio
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Jan 13, 2013, 12:59 AM

Post #5 of 13 (3102 views)
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Re: [Ron.M] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

Voltage reads 124.5V; (it fluctuates +/- 0.1 to 0.3). When it craps out it drops to 107-100volts.

Ron.M
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Jan 13, 2013, 1:10 AM

Post #6 of 13 (3100 views)
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Re: [esemilio] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

esemilio;.....

Looks like power supply or regulator problem....

Do you have the service manual ???

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

....
Veteran & Retired TV technician

esemilio
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Jan 13, 2013, 2:55 AM

Post #7 of 13 (3094 views)
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Re: [Ron.M] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

Ron.M,
Power supply problem is what I had concluded.

No, I do not have any manuals or any schematics - just a block diagram showing the interconnection between the boards.
Emilio

(This post was edited by esemilio on Jan 13, 2013, 2:58 AM)

Ron.M
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Jan 13, 2013, 10:10 PM

Post #8 of 13 (3078 views)
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Re: [esemilio] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

esemilio;....

IF we can't find out what it is , then we have to find out what it aint...
I have to tell you that the chances of pinpointing the exact cause of this problem online are verrry slim....

Couple of things I'd like you to try...
1)....Unplug connector J108 on the APW009 panel OR J210 on the A10338 panel...
Turn the TV on....
Read the voltage at J108 pins 6 &/or 7 for 130 vdc...
Use pins 1 &/or 2 for your "-" or ground connection...
Leave the set on for about 20 mins...
Then take a final reading...
Please post results...
2)...On the A10338 panel is a sub panel that sticks up on the far left side...
CAREFULLY remove that panel (Should slide up--Check for pin(s) holding it on the main panel at the bottom of the sub-panel)...
There are some small controls (Adjustments) on that panel...
Do NOT move or disturb them in ANY way...
Check ALL the solder connections on the bottom edge of the sub-panel..
IF you are good at soldering , resolder all the connections to be safe..
Carefully reinstall the sub-panel back on the A10338 panel...
Check to make sure that the panel IS CORERECTLY back on...
It is easy to have that panel misinstalled..

When the pix "shrinks" , does it shrink at the top & bottom only , the left & right sides only or all 4 sides at the same time ???

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

...
Veteran & Retired TV technician

esemilio
New User

Jan 14, 2013, 12:35 AM

Post #9 of 13 (3075 views)
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Re: [Ron.M] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

Ron.M.,

1)Unplugged J210 on the A10338; voltage on j108 pin 6&7 and 1 for (-) jumped to 125 but quickly dropped to 0 (1to 2 sec.) when the set was turned on.

2) I had already done exactly what you stated for the subpanel (including resoldering all the connections on bottom edge of subpanel)

3) The whole picture shrinks 1" on all sides; convergence looks a bit out & color may disappear.
Emilio

Ron.M
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Jan 14, 2013, 8:17 PM

Post #10 of 13 (3069 views)
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Re: [esemilio] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

esemilio;...

OK...Thanks...

Hook up the connector(s) J210) as they were...
Get a piece of printer paper or the equivalent & make a cone out of it...
Turn on the TV & using the cone , listen as close & as safely as possible to the flyback...
Listen for what may sound as a zzzztt & the TV turns off...
Also do it again & closely watch the underside of the flyback for any tiny flashes of light or arcing just before the TV turns off...
The flyback is the largest transformer on the panel & has a red wire coming from the top...
This may sound crazy , but , immediatly after it turns off , quickly unplug the TV & sniff around the flyback for any unusual odors..

Please post results...
THANKS.... Smile

....

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

...
Veteran & Retired TV technician

(This post was edited by Ron.M on Jan 14, 2013, 8:18 PM)

esemilio
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Jan 15, 2013, 2:29 AM

Post #11 of 13 (3064 views)
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Re: [Ron.M] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

Ron.M,

Something came up and I will be away from the set for the next two weeks. I will contact when I get back.
However, 1) the set does not "turn off" unless I turn it off.
2) I will listen for the buzz but I never smelled ozone -(I assume that is what you were referring to)

Thanks For Your Time!
Emilio

esemilio
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Feb 2, 2013, 7:07 PM

Post #12 of 13 (3012 views)
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Re: [esemilio] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

Hello Ron M,
I have returned. I am convinced that the problem is in the power board and must be a broken segment on the printed board. I did not mount the board but laid it so the printed side was facing up. Using a hair blower heat gun, the problem dissappears within 5 sec after I blow hot air on the board. The problem reappears however at varying time intervals. (I have resoldered almost all points with no change).
Although I love the cabinet and do get a great picture when it is working, the replacement board is rare/unavailable and very expensive - not worth the cost.

Unless you have some technique to find the intermittent break, I am going to more on.

Thanks for your time.
Emilio

Ron.M
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Feb 2, 2013, 7:44 PM

Post #13 of 13 (3007 views)
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Re: [esemilio] 46" LXI/Magnavox Power Supply Problem [In reply to]	Can't Post

esemilio;.....

Welcome back !!!!

I'm presuming you are talking about the APW009 board...
Cracked PC boards usually do not respond to heat the way you are doing it...
Based on what you are telling me , I suspect a thermally affected component that is feeling the heat thru the board...

What I would suggest you do is to remount the board back in the way it should be...
Then figure out a way to heat specific limited parts of the board ONLY...
You can use printer paper to form "walls" & insert it perpendicular to the board to block or contain areas from the heat...
Heat up one area at a time till you get a response...
Once you get a response , make the area that you are heating up smaller ...
Then heat up those smaller areas till you get a response...
Eventually you should get it to (Hopefully) the single component that is the problem...
IF & WHEN you do , give me the number printed on the board & I'll see about getting you a replacement....
A can of Electronic Circuit Freeze spray may help speed the heating/cooling cycles along...
Use it VERRRRY carefully & do NOT allow it to cause frost on components as it turns to water & will short out circuits & cause further damage...

Where did you find a replacement board at ???
& how mich was it ???

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

...
Veteran & Retired TV technician

(This post was edited by Ron.M on Feb 2, 2013, 7:50 PM)

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