TV takes about a minute to turn on

T

Tim Chreptak

Guest
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
 
"Tim Chreptak" <timbuhr@hotmail.com> wrote in message
news:EpWnb.4200$Nm6.244016@news20.bellglobal.com...
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
Click to expand...
Are you sure a diode isn't open? Try removing the four main rectifier diodes
from the circuit and test them separately.
 
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.
 
"Tim Chreptak" <timbuhr@hotmail.com> wrote in message
news:ca9ob.4493$Nm6.297241@news20.bellglobal.com...
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.
Click to expand...
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.
 
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! ;)
 
"Tim Chreptak" <timbuhr@hotmail.com> wrote in message
news:v_Aob.4013$9j3.533416@news20.bellglobal.com...
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! ;)
Click to expand...
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 :)
 
When you look at psu waveforms be aware that chassis and mains side
of psu differ by half wave rectified mains. I think this may explain
your readings.
Use an isolation transformer and be careful.
 
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