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makitaman



Joined: 28 Aug 2008
Posts: 9
Location: woonsocket

PostPosted: Thu Aug 28, 2008 5:56 pm    Post subject: toshiba 42h81 power light on no picture Reply with quote

ive got a rear projected 6 yrs old
toshiba model # 42h81
power light comes on can hear speaker cones but no picture
i picked this up from someone who had a tech in the set
and told him the convergence board needs to be replace
i checked all the fuses
found a 1.8 ohms resistor that is burnt and they put 4 2k resistors on the exsiting 1
ive replaced that resistor
they jumpered fuse 852
and unsodered 1 heat sink from board
ive ordered ic chips for it but im thinking its a power issue
i can see the the compound coming out of the side of the stks so it looks like they were replaced cant be positve(doesnt look factory)
i have the same set already that i had to replace the chips on and there was minimal compound on the chips.
ive heard of resoldering jumpers but i dont know the locations.
any ideas
tom
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makitaman



Joined: 28 Aug 2008
Posts: 9
Location: woonsocket

PostPosted: Sat Aug 30, 2008 7:51 pm    Post subject: Reply with quote

ive replaced the ic's and still no pic.
and they were definately changed already.
im thinking the flyback is gone.
nervous to start stickin my meter in there.
i have schematics can anyone point me to the best way to meter around in there.
thanks tom
Jesse Mack



Joined: 22 May 2008
Posts: 600
Location: The Last Frontier

PostPosted: Tue Sep 02, 2008 9:03 am    Post subject: Reply with quote

Do the IC heat sinks get warm??

If they do not, check fuses F852 - 2AMP, F853 - 1.25AMP, F850 & F851 - ALL 5AMP on the power deflection pcb. THESE ARE NOT GLASS FUSES. They are usually about the size of a 1 watt resistor and either green or orange in color. They are soldered in. The nomenclature is printed on the component side of the board. They are all about centered on the opposite edge of the PCB as the high voltage transformer.

If you have cleaned up the mess you describe you most likely have one of these fuses blown.

Hope this helps

Jesse
makitaman



Joined: 28 Aug 2008
Posts: 9
Location: woonsocket

PostPosted: Tue Sep 02, 2008 11:30 am    Post subject: Reply with quote

i have 7 black fuses that i have checked and not found an open
if i can find out where the commons for these fuses i can meter them hot and see the voltage going through them. ive checked the power to the ic's using pin 1 as common and pins 4 and 5 should be at 22 volts and there at .3 volts. which would tell me they are dead.
Jesse Mack



Joined: 22 May 2008
Posts: 600
Location: The Last Frontier

PostPosted: Wed Sep 03, 2008 9:19 am    Post subject: Reply with quote

I do not know how to describe fuse location any better. See previous post. Just measure DC levels on both ends of these fuses while set is on. Using the tuner shielding as ground.
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makitaman



Joined: 28 Aug 2008
Posts: 9
Location: woonsocket

PostPosted: Wed Sep 03, 2008 11:17 am    Post subject: Reply with quote

ok ive tested to all kinds of shields and get nothing on both sides of fuses
but i got voltage on both sides of main fuse
fuse locations i tested were f850 f851 f852 f853 f490 f870 f891
i c 2 more in the high voltage side f860 and f801 that i havent checked yet.
makitaman



Joined: 28 Aug 2008
Posts: 9
Location: woonsocket

PostPosted: Wed Sep 03, 2008 11:51 am    Post subject: Reply with quote

801 is the main and teseted fine
f860 has been tested no voltage either side and is closed
Jesse Mack



Joined: 22 May 2008
Posts: 600
Location: The Last Frontier

PostPosted: Wed Sep 03, 2008 3:37 pm    Post subject: Reply with quote

The main fuse F801 is on the primary side of the SWPS and is AC (Alternating Current)voltage.. When measuring any of the other fuses you need to be in DC (Direct Current) mode with your meter. F860 must be measured from Hot ground for a proper voltage measurment.All other fuses listed must be measured from Cold ground (Tuner shield etc) and your meter must be in DC mode.

Hope this helps

Jesse
makitaman



Joined: 28 Aug 2008
Posts: 9
Location: woonsocket

PostPosted: Thu Sep 04, 2008 11:33 am    Post subject: Reply with quote

yes i see the main voltage on ac no problem. and on dc to the other fuses i read no voltage using the tuner shield
Jesse Mack



Joined: 22 May 2008
Posts: 600
Location: The Last Frontier

PostPosted: Thu Sep 04, 2008 1:14 pm    Post subject: Reply with quote

First, When you turn the set on do you hear a relay click. If no relay clicks stop there and advise.

If there is a relay click, check for momentary DC at the fuses for maybe one to two seconds after the click.

Jesse
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