I'm working on a magnavox that's behaving very erratically.
I've done a lot of research,
and something jumped out at me, in this thread. The mainboard could be my problem, but I ordered one off ebay and it didn't make any difference, note that it was sold "as is", and could've dead to begin with. 
dgtech links to a service manual (for a different set, with a nearly identical design) at ElectroTanya.
http://elektrotanya.com/philips37mf321d-37_chassis_tpe1.0u--la_sm.pdf/download.html
It appears to be a dead link? I've downloaded PDFs from there before, and for some reason I don't see a download button on that page (even with adblock and NoScript disabled)
Anyway, let me start at the beginning.
The swollen caps were probably just the tip of the iceberg...
Here's what I did, in order:
- 1. Opened the TV, saw two swollen caps in the upper left side of the PS. Replaced these, and still got the same symptom: The TV would turn on, with a black screen, but the backlight was ON.
- 2. The TV sat in storage for several weeks... I decided to have another crack at it.
I hit the power button, and IT CAME ON!
Only for about 10 glorious minutes I was able to change channels, volume and even enter the on-screen menu. Then it shut off, and the TV's relay clicked, 5 seconds went by... clicked again as if it was turning on by itself, but it didn't, just a flashing power LED and the backlight was OFF. every 5 seconds this cycle would repeat again.
Only way to get it to stop was unplugging the set.
Voltages going up/down, not a good sign, right?
And then the symptoms change again!
-10. I take a closer look at the lone capacitor, 2074, in the upper-right of the power board. The original says Elite 25v 2200uf. thanks to the knowledgeable folks here, I now know it's crap. It's not bulging, but who's to say it hasn't failed? I replace it with a Sam Wa 25v 2200uf 105c.
This is where things get weird, instead of a clicking cycle, I get a flicker from the backlight for a split second. This always happens as soon as I plug it in, no need to hit power. (but if I do hit power, it flickers once more).
Maybe the Sam Wa is a crappy brand too? So I replace it with a SAMSUNG 25v 2200uf 85c. No dice. It still flickers for a split second.
Sorry for the long OP. But I hope it helps narrow things down. Any ideas?
I've done a lot of research,
and something jumped out at me, in this thread. The mainboard could be my problem, but I ordered one off ebay and it didn't make any difference, note that it was sold "as is", and could've dead to begin with. dgtech links to a service manual (for a different set, with a nearly identical design) at ElectroTanya.
http://elektrotanya.com/philips37mf321d-37_chassis_tpe1.0u--la_sm.pdf/download.html
It appears to be a dead link? I've downloaded PDFs from there before, and for some reason I don't see a download button on that page (even with adblock and NoScript disabled)
Anyway, let me start at the beginning.
The swollen caps were probably just the tip of the iceberg...
Here's what I did, in order:
- 1. Opened the TV, saw two swollen caps in the upper left side of the PS. Replaced these, and still got the same symptom: The TV would turn on, with a black screen, but the backlight was ON.
- 2. The TV sat in storage for several weeks... I decided to have another crack at it.
I hit the power button, and IT CAME ON!
Only for about 10 glorious minutes I was able to change channels, volume and even enter the on-screen menu. Then it shut off, and the TV's relay clicked, 5 seconds went by... clicked again as if it was turning on by itself, but it didn't, just a flashing power LED and the backlight was OFF. every 5 seconds this cycle would repeat again.
Only way to get it to stop was unplugging the set.
Voltages going up/down, not a good sign, right?
- 3. When I plugged it back in a half hour later, it did the same cycle. So out comes the multimeter and checked the plug from the PS board to the mainboard. All voltages looked OK except pin 1 which started at about 16v and would drop to 13v when the relay clicked. Then back to 16v... 13v... back and forth.
The next steps were done with ONLY the AC plugged in, the two connectors were loose.
-4. Following PlainBill's advice, I checked main filter cap, and it reads 160v
-5. Checked the small black tube shaped component at 5057 / 9051. I think it's a bridge rectifier, but I could be wrong. (it has a uuu symbol on the solder-side). It reads 3.5k Ohms, both ways (it's a 2-pin component, so there's only two ways of measuring). I checked the identical black tube at 5056 / 9052 and that showed 5.7k Ohms, again, both ways.
-6. Checked the mustard yellow varistor at 3072. Reads 15k Ohms, both ways.
-7. Checked all voltages on both connectors
Mainboard connector (upper-right):
Pins 1, 2 = 16.7v
Pin 3 = 23.8v
Pin 4 = 0.00
Pin 5 = 0.01 (I'm guessing this and pin 4 are signals?)
Pins 6, 7, 8 = GND (All 0.00v)
Pin 9 = 0.00v
Pin 10 = 0.00v (based on the traces, I think 9 and 10 are also signals)
Inverter Connector
Pins 1, 2, 3, 4 and 5 are ALL 0.01v, --probably signals
Pins 6, 7 = 0.00v (did more tracing... shouldn't these two be 24v ???)
Pins 8, 9, 10, 11 and 12 all read 0.00v, are they all GND?
-8. Checked the Volt Regulator at 9058. Black probe on the pin labeled "G", Red on "D", gives a readout of 23.5v, so why isn't that getting to the plug?
-9 Hooked everything back up and retested, reads 0.55v at pins 6 and 7
The next steps were done with ONLY the AC plugged in, the two connectors were loose.
-4. Following PlainBill's advice, I checked main filter cap, and it reads 160v
-5. Checked the small black tube shaped component at 5057 / 9051. I think it's a bridge rectifier, but I could be wrong. (it has a uuu symbol on the solder-side). It reads 3.5k Ohms, both ways (it's a 2-pin component, so there's only two ways of measuring). I checked the identical black tube at 5056 / 9052 and that showed 5.7k Ohms, again, both ways.
-6. Checked the mustard yellow varistor at 3072. Reads 15k Ohms, both ways.
-7. Checked all voltages on both connectors
Mainboard connector (upper-right):
Pins 1, 2 = 16.7v
Pin 3 = 23.8v
Pin 4 = 0.00
Pin 5 = 0.01 (I'm guessing this and pin 4 are signals?)
Pins 6, 7, 8 = GND (All 0.00v)
Pin 9 = 0.00v
Pin 10 = 0.00v (based on the traces, I think 9 and 10 are also signals)
Inverter Connector
Pins 1, 2, 3, 4 and 5 are ALL 0.01v, --probably signals
Pins 6, 7 = 0.00v (did more tracing... shouldn't these two be 24v ???)
Pins 8, 9, 10, 11 and 12 all read 0.00v, are they all GND?
-8. Checked the Volt Regulator at 9058. Black probe on the pin labeled "G", Red on "D", gives a readout of 23.5v, so why isn't that getting to the plug?
-9 Hooked everything back up and retested, reads 0.55v at pins 6 and 7
And then the symptoms change again!
-10. I take a closer look at the lone capacitor, 2074, in the upper-right of the power board. The original says Elite 25v 2200uf. thanks to the knowledgeable folks here, I now know it's crap. It's not bulging, but who's to say it hasn't failed? I replace it with a Sam Wa 25v 2200uf 105c.
This is where things get weird, instead of a clicking cycle, I get a flicker from the backlight for a split second. This always happens as soon as I plug it in, no need to hit power. (but if I do hit power, it flickers once more).
Maybe the Sam Wa is a crappy brand too? So I replace it with a SAMSUNG 25v 2200uf 85c. No dice. It still flickers for a split second.
Sorry for the long OP. But I hope it helps narrow things down. Any ideas?
Attached Files
Comment