1994 Sanyo TV, turns on, no picture, turns right back off.
 

Here's all the info listed on the back of the TV:
http://i40.tinypic.com/b4iaoj.jpg

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?

Sounds like a shorted HOT.

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.

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.

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.

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.

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

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

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.

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.

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.

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.

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...

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

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.

There are three large ceramic resistors near the HOT. None of them have any info on them though.

I'll check all the resistors in the area in a bit...

Okay, so far I haven't found any "bad" resistors. The two larger 10 watt ceramic resistiors in the regulator circuit have seen some heat... so much that their casing is cracked. The info on them was worn away, but my multimeter identified them as 220 ohm resistors. I'm sure as hell going to replace them, but they tested good, so i assume they aren't why the TV still won't get a picture.

Okay I took out the third ceramic resistor, and it measures about 10 ohms. I don't know if its good or bad because the information on it is cryptic.

The info is: RY8GJ 6R8K I assume the K stands for kilo ohms, so that would indicate the resistor is bad, but I can't be certain.

I think that may be a 6.8 ohm. All the bad ones that I've seen were open. I've never seen one of those go up or down in value.

Okay, I'll replace it anyway since it's out of spec.

I also found a 2.5K ohm resistor in the flyback area that reads only ~175 ohms. Pretty sure it's supposed to be a 2.5k ohm resistor. Here's a pic of it.
http://i40.tinypic.com/2hmgi07.jpg

To me it reads red green red gold, which comes out to 2500 ohms at 5% tolerance.

It's in Sams 3466. I'll see if I have a copy so we can make sure of the resistor values.

Oh that would be great. :) I HATE resistor color bands. Can't ever tell with 100% certainty what one of those little 4 band bastards is. So i snap a pic of it and use Photoshop's color sampler to get a best guess.

I found the Sams. What are the board location numbers of those two resistors in question?

As far as the shorted HOT blowing something, I'd suspect R007 (5.6 ohm, 2 watt) and/or R001 (1 ohm, 6 watt). One end of R001 connects to one of the contacts on the power relay and the other end connects to the cathode of D002 and the anode of D004. These are two of the four diodes that make up the bridge rectifier in the power supply and the cathode is the end of the diode with the white or silver band.

R007 connects to pin 3 of the regulator.

If these resistors are good, measure the B+ voltage. Take your voltmeter ans set it to measure at least 200 volts DC. Connect the negative lead to one of the heatsinks and the positive lead to pin 4 of the STR regulator IC or pin 2 of the flyback. Turn the set on and you should measure around 130 volts DC. If the voltage is much higher, like in the 160 volt range, either the regulator circuit is not operating properly or the horizontal circuit is not operating. These types of regulators must have a proper load in order to regulate properly.

If the voltage is lower than 130, unsolder pin 2 of the flyback and check again. If the voltage jumps up, the flyback is most likely bad.

Okay, the supposedly 6.8 ohm ceramic block resistor is R473

The supposedly bad 2.5k ohm resistor is R459

R473 is a 6.8 ohm and R459 is a 180 ohm, 1 watt.

Okay, so they're both essentally good... R473 might be a tad high. Thanks a lot! Saved me from spending money on the wrong parts, getting frustrated and junking the chassis.

I'll check R001 and R007 when i can.

R007 is BAAAAD!! Infinite ohms! Finally found you motherfucker!

And of course it's hidden between the big 220 ohm resistors and the heat sink, so were it not for your help, I may have never ever ever found it.

While you're in there, check C474, a 47uf, 160 V cap.

All right. I've been shotgunning the jamicons anyway. The rubycons seem to be holding up nicely.

Oh, C474 was one of the first caps I replaced. So that's already been replaced.

Still waitin on the parts I need.

Well, I replaced the bad resistor, put it all back together and... nothing! same problem.

I went through all the trouble of getting the needed parts for nothing!

I think I'd check the voltage at the collector terminal (center pin) of the HOT. Just set your meter to measure at least 200 volts DC and clip the negative lead to one of the chassis heatsinks. Attach the positive lead to the HOT collector and hit the power button. You should have around 130 volts DC. Since the set is dead, you'll likely either read very low or zero volts or a high reading of around 170 volts. If the voltage is low or zero, you'll have to trace the B+ line back to the STR30130 to find the problem.

I did that, and got a whopping... 2 volts.

So I assume something's bad between the center pin of the HOT and the regulator IC?

Take out the HOT and recheck the voltage. If it jumps up, the flyback is probably bad and loading down the voltage.

Seeing as there isn't much between the center pin of the HOT and the flyback, can I just assume the flyback is bad? This TV's quickly turning into more trouble then it's worth.

I guess I could take the HOT out and test again, but where would i clip the positive lead to?

Trace the foil back and connect it to the flyback terminal that goes to the HOT.

Okay, I removed the HOT, and connected my positive lead to the flyback pin, which was easy enough to find. Turned the TV on, and still only read about 2 volts.

WTF...

OK, I'll dig out the schematic again. The problem has to be somewhere in the power supply.

I just had another thought while I re-locate the schematic. Locate the main filter cap in the power supply. That's the huge cap with a value between 330 uf and 680 uf at 180 to 200 volts. Connect your voltmeter to the positive terminal of that cap and the negative lead to ground and see what you get. Should be around 165-170 volts.

It's a 470uf@ 200 volt cap. Okay I'll do that.