Home |
Search |
Today's Posts |
|
Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
|
|||
|
|||
TV takes about a minute to turn on
I am just getting into repair, so I have ZERO experience to work with, and
nobody to ask questions, so this is my only hope. I had a TV(VICON VM621, made by Hantarex?) given to me and it was totally dead. Relying on what I could remember from school and various articles I've read on the net, I determined the main input power resistor was blown, along with the HOT. I replaced both, checked all the other major transistors and caps, and used a variac to bring up the power. Voila, set turned on fine. I was happy. Next day i turned it off to replace the back cover, and then it wouldn't turn on. I didn't realize I had turned the variac to about 130VAC by the time the set fired up. On normal line voltage, the set takes about a minute to fully fire up, it's like the power slowly climbs, and once it's up there it's fine. After you flick the switch, there is nothing at all, then you start to hear the speaker going 'pop pop pop' then the tube sounds like it's trying to charge, then eventually everthing fires up... I replaced both filter caps (2x470uF 200V) with little improvement. when i put my scope on the filter cap i have an enormous ripple @120Hz, from 0V to way over 100V. I wish it was a simple diode shorted but they all check out fine. everything up to the large capacitors seems to be ok, but then again i've overlooked stuff in the past. Please anybody that can give me any ideas, with as much support information as possible so i can carry out the suggestion, I'd be in great debt. Thanks in advance... Tim |
#2
|
|||
|
|||
TV takes about a minute to turn on
"Tim Chreptak" wrote in message .. . I am just getting into repair, so I have ZERO experience to work with, and nobody to ask questions, so this is my only hope. I had a TV(VICON VM621, made by Hantarex?) given to me and it was totally dead. Relying on what I could remember from school and various articles I've read on the net, I determined the main input power resistor was blown, along with the HOT. I replaced both, checked all the other major transistors and caps, and used a variac to bring up the power. Voila, set turned on fine. I was happy. Next day i turned it off to replace the back cover, and then it wouldn't turn on. I didn't realize I had turned the variac to about 130VAC by the time the set fired up. On normal line voltage, the set takes about a minute to fully fire up, it's like the power slowly climbs, and once it's up there it's fine. After you flick the switch, there is nothing at all, then you start to hear the speaker going 'pop pop pop' then the tube sounds like it's trying to charge, then eventually everthing fires up... I replaced both filter caps (2x470uF 200V) with little improvement. when i put my scope on the filter cap i have an enormous ripple @120Hz, from 0V to way over 100V. I wish it was a simple diode shorted but they all check out fine. everything up to the large capacitors seems to be ok, but then again i've overlooked stuff in the past. Please anybody that can give me any ideas, with as much support information as possible so i can carry out the suggestion, I'd be in great debt. Thanks in advance... Tim Are you sure a diode isn't open? Try removing the four main rectifier diodes from the circuit and test them separately. |
#3
|
|||
|
|||
TV takes about a minute to turn on
Thanks, I removed the 4 diodes, none were open but one didn't check out
exactly like the others so I replaced all 4. I also removed and re-checked the bypass caps around there and everything seems fine, but when i look at the wave going to the large capacitors it looks totally unrectified. It's from about 0V up, but I'm sure thats just because the cap's are working as much as they can to maintain some DC. Is it possible this is more complicated than I'm thinking and its feedback from somewhere further down, not from the main PS? it's 60Hz (i don't know why i thought it was 120Hz yesterday) as much as I can tell from reading the scope. I really wish i had a schematic, that would at least give me a chance... I would think something is really loading down the supply but I have a 1A fuse inplace of the recommended 3.15A and it hasn't blown once yet, nor does the input resistor get hot. Those caps however seem to discharge almost instantly. Thanks again for any comments, ideas, criticisms, etc. |
#4
|
|||
|
|||
TV takes about a minute to turn on
"Tim Chreptak" wrote in message .. . Thanks, I removed the 4 diodes, none were open but one didn't check out exactly like the others so I replaced all 4. I also removed and re-checked the bypass caps around there and everything seems fine, but when i look at the wave going to the large capacitors it looks totally unrectified. It's from about 0V up, but I'm sure thats just because the cap's are working as much as they can to maintain some DC. Is it possible this is more complicated than I'm thinking and its feedback from somewhere further down, not from the main PS? it's 60Hz (i don't know why i thought it was 120Hz yesterday) as much as I can tell from reading the scope. I really wish i had a schematic, that would at least give me a chance... I would think something is really loading down the supply but I have a 1A fuse inplace of the recommended 3.15A and it hasn't blown once yet, nor does the input resistor get hot. Those caps however seem to discharge almost instantly. Thanks again for any comments, ideas, criticisms, etc. Well the fact that it gets better as it warms up really points to a capacitor somewhere, perhaps you're barking up the wrong tree and it's somewhere in the horizontal section. Look closely for any that may be bulging at the top or leaking, and you could try a can of freeze spray, wait until the set comes up then give each electrolytic a quick shot and see if it shuts down. |
#5
|
|||
|
|||
TV takes about a minute to turn on
Many many thanks on the insight James,
After replacing a few large suspected caps the problem was reduced but still there. I got some cold spray and found one more small electrolytic that would cause the set to 'choke' when i gave it a shot. Replaced that one and everything fired up beautifully. At least I learned quite a few troubleshooting techniques fixing this TV... bring on the next one! |
#6
|
|||
|
|||
TV takes about a minute to turn on
"Tim Chreptak" wrote in message .. . Many many thanks on the insight James, After replacing a few large suspected caps the problem was reduced but still there. I got some cold spray and found one more small electrolytic that would cause the set to 'choke' when i gave it a shot. Replaced that one and everything fired up beautifully. At least I learned quite a few troubleshooting techniques fixing this TV... bring on the next one! Nice feeling isn't it? Now that you've got some experience you're well on your way, now you just need to keep an eye out on trash day, or if there's a free classified ad thing around you, you could place an ad looking for free broken TV's, though if you have a wife you may soon find either yourself or the TV's out on the street :-) |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
kitchen cupboard rubbish bin which takes carrier bags | UK diy | |||
Sony Model KV-32XBR48 slow turn on and flashing video for short period at turn on | Electronics Repair | |||
Zenith Model SY3288DT 32" TV WILL NOT TURN ON | Electronics Repair |