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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Fri 27, 2017 11:39 am 
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Hey Brian,

Findm-Keepm wrote:
Sure. Just be careful around the the neck of the CRT and the small circuit board with the CRT socket.


Sounds good. Just woke up, so going to make coffee, eat breakfast, and get after it. Photos incoming in a few hours.

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Fri 27, 2017 3:11 pm 
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Hey Guys,

Doctor Randall starts the operation:
Attachment:
TV.jpg
TV.jpg [ 66.04 KiB | Viewed 322 times ]


Wish the "patient" luck! :D

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Fri 27, 2017 11:42 pm 
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Re-Howdy Guys,

Okay. I did more research and found this manual: http://archivos.diagramas.mx/televisores/Sanyo%20chassis%20AVM-2780G%20(training).pdf. I'm pretty sure this is the right manual for the DS27590-03 chassis, but not 100% positive. Everything I've read says that it's the main service manual for the DS27590-00, 01, 02, and 03 chassis', and then all you have to do is pay attention to the service bulletins for the individual sub-chassis. Fine with me. I'll start reading the manual and see what I can learn. It looks pretty straightforward so far.

After vacuuming the PCB, I did a visual inspection and found a dark, black area around some components, located next to/around the power supply. Here's a shot of what I found (sorry about the crappy quality):

Attachment:
over_heated.jpg
over_heated.jpg [ 54.04 KiB | Viewed 306 times ]


You can't really notice it in the picture, but most of board around those parts is blackish tinged, as in showing that they've been around a lot of heat. The big resistors are even mounted up off the board aways, so I suspect this is an area known for a lot of heat or something?

Now, how in the heck do I power up the board and stay away from that damn flyback and tripler circuit and do some voltage measurements without shocking myself and burning the phosphorus off the CRT? I take it I can just disconnect the Anode clip and tape that puppy out of the way and I'll be good?

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Sat 28, 2017 12:30 am 
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If you can turn the brightness down low enough I wouldn't bother disconnecting the anode. If you disconnect it you still have to keep away from it, why not just leave it where it is.
The darkened board is typical of heat effecting it. By itself it doesn't mean much. I believe the the four pin IC that happens to be in the photo is a opto-isolator that is between the hot side of the power supply and the rest of the chassis. In other words one side of the power supply has connection directly to the power cord. You really should have an isolation transformer but I don't suppose you do. So be very careful with connecting test equipment that might be grounded through the power cord.

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Sat 28, 2017 1:36 am 
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Howdy Tim,

Notimetolooz wrote:
If you can turn the brightness down low enough I wouldn't bother disconnecting the anode. If you disconnect it you still have to keep away from it, why not just leave it where it is.
The darkened board is typical of heat effecting it. By itself it doesn't mean much. I believe the the four pin IC that happens to be in the photo is a opto-isolator that is between the hot side of the power supply and the rest of the chassis. In other words one side of the power supply has connection directly to the power cord. You really should have an isolation transformer but I don't suppose you do. So be very careful with connecting test equipment that might be grounded through the power cord.


Yeah, I still have to wait until xmas to get all of my test gear, and I don't have an isolation transformer. What I think I'm going to do is finish reading those service bulletins and put the thing aside until I get that isolation transformer, just to be on the safe side. I'll get back to this thread when I have everything set up.

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Sat 28, 2017 3:00 am 
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You can measure voltages with a battery-powered VOM, since it'll be unconnected to the power line. To free up your hands, use insulated clip leads between the VOM's probes and the points you want to measure. That way you can connect the meter with the power off, then turn on the set and see what the voltage is. It's slow, but safe for you and the set.

You might need small test clips to fit on the IC pins. Lots of different types are available. If all else fails you can solder a wire to the points (such as IC pins) to be measured and connect the clip leads to the wire. I've done this many times with circuit points that are not safely accessed with power on, or otherwise inaccessible.

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