1994 Sanyo TV, turns on, no picture, turns right back off. - Videokarma.org TV - Video

MRX37 · #1 03-25-2009, 02:54 PM

Here's all the info listed on the back of the TV:

I press the power button, and I hear the degaussing circuit, as well as a faint hum in the speakers. I do not hear the CRT scanning. The TV shuts itself off a few moments later.

Doing a google search, it appears this problem is fairly common with this model, but alas, there are quetions but no answers, other then "buy a new TV".

Do you guys have any ideas?

zenith2134 · #2 03-25-2009, 02:55 PM

Sounds like a shorted HOT.

MRX37 · #3 03-25-2009, 03:01 PM

Okay. I'll check the HOT as soon as I can... having a 36 inch Sanyo that also had a bad HOT, I believe you... and I'll check the caps around the HOT.

radiotvnut · #4 03-25-2009, 03:03 PM

Sounds like a shorted HOT to me as well. If it uses an STR30130 or similar voltage regulator IC, it may be bad also. You could also have a bad flyback; but, they are inexpensive and this set would be worth a new flyback if it's not beat up.

zenith2134 · #5 03-25-2009, 03:45 PM

Yeah, try to find out what blew the HOT if it is indeed bad. Radiotvnut has it right, the regulator could also be bad.

OT: Interesting how my '85 Sanyo and your '94 are both built in USA with Japanese parts. I know Matushita Quasars were the same.

radiotvnut · #6 03-25-2009, 03:53 PM

I forgot to mention that there's a resistor in the regulator circuit that may be open. Years ago, I fixed a 19" Sanyo from the same time period that had a shorted HOT and voltage regulator. After I replaced the parts, the set played; but, the B+ was low and unregulated. There was a 1 or 2 watt power resistor connected to the regulator that was open. I don't remember the exact value; but, there are few parts in those STR30xxx based regulator circuits, so finding the problem shouldn't take too long. Frankly, they should have stuck with that type of regulator. They are simple, cheap, and easy to troubleshoot. I can't say the same for the much more complex switching power supplies used in newer electronics.

MRX37 · #7 03-25-2009, 04:11 PM

All right. I'll check the HOT and everything around the HOT that I can.

MRX37 · #8 03-25-2009, 04:35 PM

I see an STR30130 IC How do I test to see if it's bad?

radiotvnut · #9 03-25-2009, 04:43 PM

You can check between all of the pins with an ohmmeter to reveal a shorted device. Otherwise, you'll have to get the set to stay on and check the B+ voltage.

One other thing. If there's an electrolytic cap in B+ line, check it. It will have a voltage rating of at least 160 volts.

MRX37 · #10 03-25-2009, 04:53 PM

The HOT (D1879) is certainly bad. low ohm readings on all three pins. Good news is I'm certain I have a better HOT to throw in.

If the IC's bad, that might be another story, unless i can substitute another IC...

I'll check the caps and the IC and see what i find.

MRX37 · #11 03-25-2009, 05:03 PM

I found a 47uf@160 volt Rubycon cap near the flyback that tests at... 55.3uf Isn't that a little high, and is this an issue?

tested the IC, and I'm getting high ohm readings on at least 3 of the pins, with a couple others reading infinite ohms. I doubt its shorted.

radiotvnut · #12 03-25-2009, 07:18 PM

I'd be worried more if the cap was lower in value. At this point, I'd throw a HOT at it and see what happens.

MRX37 · #13 03-25-2009, 08:21 PM

Changed the 47uf cap anyway, and a bad 220uf@ 16 volt cap that was in the flyback area.

Tonight was a good night for TV's. I have two more that I'm gonna get to after I deal with this one...

MRX37 · #14 03-25-2009, 08:42 PM

Threw in a new HOT, no joy. still can't hear the CRT scanning.

radiotvnut · #15 03-25-2009, 08:52 PM

Also check for an open fuse type resistor. It will probably be a white ceramic low ohms 5 or 10 watt resistor. There may be a smaller size fusible resistor between the voltage regulator output and the B+ input pin of the flyback. When the HOT shorts in sets that use the STR30xxx based power supply, it usually opens a fuse or fusible resistor.