Sanyo CPT3240 no image troubleshooting

[vol.2]

It could be a component in the power supply or something downstream loading it down. Either is possible.

Originally Posted by ostlar

I've checked it thoroughly for cracked solder joints four times now, I see nothing.

That means nothing. Many, possibly most, cracked solder joints can only be seen with a microscope. What happens is that they heat up and expand as and then start to develop a layer of corrosion at the interface

You could have cracked solder joints all over the place and end up chasing your tail around looking for a ghost

There are some electrolytic caps marked "NP" which I'm guessing is non-polar?

Yes. NP or BP both mean non-polar or bipolar. Same thing.

I think you need to hunt for the schematic. You need to see what's connected to that resistor that's smoking and test it all

I tried to find a manual and struck out as well. They might know something over on the antique radio forum.

Another thought is that this chassis is probably used by a different US retailer like Sears or some department store, and you would have infinitely more luck finding that service manual, if you could figure out what the alternative model/chassis number is. I took a quick look on Sam's for something that might match and couldn't find it, but maybe someone here or elsewhere might recognize it

without the schematic, I wouldn't be too much use for you doing remote troubleshooting. Username1 and Zeno are the heavy hitters here, and they might have some things to try

Best I can suggest at this point is to look what the resistor that heats up is connected to by traces and start testing everything you find. There's definitely a bad part in there if it's smoking

[ostlar]

Originally Posted by vol.2

That means nothing. Many, possibly most, cracked solder joints can only be seen with a microscope. What happens is that they heat up and expand as and then start to develop a layer of corrosion at the interface

You could have cracked solder joints all over the place and end up chasing your tail around looking for a ghost

Fair point, I could try to reflow all of the solder joints. It would be a tedious task, but an important one when diagnosing. I might need to print out an image of the board to mark the solder joints I've reflowed, so I don't miss any.
I've tried giving it the percussive maintenance by lightly tapping the board with the back of my screwdriver while powered on to see if there is any cracked joints. Probably made more cracked joints by doing that.

I want to get this thing to work again, it's just a matter of not giving up. For most people it's not worth the time and effort, but for me it's a learning experience and a way to save a CRT which I think is important. I've fixed several other CRTs, but they have had clear symptoms and usually have had a simple fix like a visible cracked solder joint or a leaky capacitor.

Thanks for the moral support, it really helps!

Next thing would be to focus more on getting the schematics. Someone somewhere probably have them in paper format, I might have to ask around.

EDIT: Oh and I forgot to mention that I could hear the degaussing coil on a cold startup, so that works at least.

[vol.2]

Originally Posted by ostlar

I might need to print out an image of the board to mark the solder joints I've reflowed, so I don't miss any.

Typically, the best place to start is the heavy components like transformers, power transistors, power resistors, anything with a heatsink, and with anything that takes physical stress of any kind like a connector, switch or board-to-board wiring.

If you reflow all of that, you have probably covered your bases. Sometimes you'll find the odd loose part that you don't expect, but it might not be the best way to spend you time doing the entire board.