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proscan 47lb45h no picture, sound or backlight   Goto page 1, 2  Next  
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adh



Joined: 12 Aug 2011
Posts: 8

PostPosted: Fri Aug 12, 2011 12:44 pm    Post subject: proscan 47lb45h no picture, sound or backlight Reply with quote

I have a proscan 47lb45h that I am trying to fix for a friend. When plugged in I get the amber standby light and the light will switch to blue when the power button is pressed. However, I get no picture, sound, or backlight. I checked every cap and found no problems. I also tried to apply heat to the caps because I heard it will briefly restore capacitance to failing capacitors. That didn't get me anywhere either. All of the cables are also in good shape. I tested all of the voltages on the power supply board and they seem to be working correctly. I lifted the power supply board and the main board to check the solder joints and they look fine too. I tried for hours to find a repair manual for this model and came up empty. I'm thinking the processor or one of the control circuits on the main board went out but I would really appreciate some more suggestions before I tell my friend he's going to have to pay a small fortune for a new board. Thanks for any help!
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kuhurdler



Joined: 28 Dec 2006
Posts: 2862
Location: Overland Park, KS

PostPosted: Fri Aug 12, 2011 12:52 pm    Post subject: Reply with quote

what method did you use to check the caps.
What voltages is the power supply outputting?
adh



Joined: 12 Aug 2011
Posts: 8

PostPosted: Fri Aug 12, 2011 1:04 pm    Post subject: Reply with quote

Visual inspection for bloating, leaks, and burns. I also heard that heating a failing cap with a hair dryer will make it work again while heat is applied. Unfortunately, I don't have a meter here that can test caps. I'm getting 5V, 12V, and 24V on the supply. I'll have to check again, but there was a 3.2V on a pin that wasn't labeled with a voltage.
adh



Joined: 12 Aug 2011
Posts: 8

PostPosted: Fri Aug 12, 2011 1:22 pm    Post subject: Reply with quote

I have 14.8V out of two pins that are supposed to be 14V but that seems to be within tolerance. The 3.2V is on a pin that looks like it's labeled ER2, but it's hard to read. The cable goes from the power supply to the board on the left labeled master.
kuhurdler



Joined: 28 Dec 2006
Posts: 2862
Location: Overland Park, KS

PostPosted: Sat Aug 13, 2011 12:59 pm    Post subject: Reply with quote

a visual cap inspection is very unreliable. They may still be bad. Your voltage levels sound fine. I don't really have any ideas for you from here. Hopefully someone else can help.

Heating up circuitboards is really only a good idea if your troubleshooting a TV goes from normal to failing as it warms up... and then works normally when it's cold again. I personally wouldn't recommend heating any caps to try to see if their failing TV suddenly starts working.
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adh



Joined: 12 Aug 2011
Posts: 8

PostPosted: Sat Aug 13, 2011 5:41 pm    Post subject: Reply with quote

I just ordered a new main board from sears. Hopefully it solves the problem.
adh



Joined: 12 Aug 2011
Posts: 8

PostPosted: Fri Aug 19, 2011 12:11 am    Post subject: Reply with quote

The new main board came today. It seems to have made the timeout to standby and input auto-detection start working, but didn't solve the other issues. I'm going to try to replace the capacitors on the supply board tomorrow. Does anyone have an opinion on whether or not I should try to replace the supply board if the new capacitors don't work? Like I said before, the voltages look like they are correct. It seems almost like the backlight or lcd panel gave out, but the sound isn't working either. Since the main board appears to be working correctly, shouldn't the sound work by hitting the input button until I hit the one that's connected? All of the sound circuitry is on the main board and it seems to be powered correctly. I would really appreciate any comments or ideas on this.
2004FLHRSI



Joined: 13 Aug 2011
Posts: 5

PostPosted: Fri Aug 19, 2011 11:52 am    Post subject: Reply with quote

adh wrote:
The new main board came today. It seems to have made the timeout to standby and input auto-detection start working, but didn't solve the other issues. I'm going to try to replace the capacitors on the supply board tomorrow. Does anyone have an opinion on whether or not I should try to replace the supply board if the new capacitors don't work? Like I said before, the voltages look like they are correct. It seems almost like the backlight or lcd panel gave out, but the sound isn't working either. Since the main board appears to be working correctly, shouldn't the sound work by hitting the input button until I hit the one that's connected? All of the sound circuitry is on the main board and it seems to be powered correctly. I would really appreciate any comments or ideas on this.


It is true, that on some electrolytics, re-warming them can cause them to have added capacitance. But when they cool, they lose it. I've had this occur in several switching supplies (mainly computer type) where the customer turns off the computer at the end of the day and the next day, it's no-go. Best use I've found for an old hair dryer in my service truck when I'm stuck and don't have a spare supply in-stock. Warm the entire supply for 10 minutes right thru the vent and they usually spring back to life. Customer is happy they get to work while I wait for delivery on the new supply.

Since you have some voltages, I don't know if that's your issue or not, but most hair dryers won't damage anything except hair and it's worth a try to warm them up as an aid to learning more.

Good luck!
adh



Joined: 12 Aug 2011
Posts: 8

PostPosted: Fri Aug 19, 2011 2:19 pm    Post subject: Reply with quote

Thanks for the reply! I couldn't get the caps today, so I'm going to have to order them in from digikey. I'll have to give the hairdryer trick another try while I'm waiting. Maybe I didn't heat them long enough.
adh



Joined: 12 Aug 2011
Posts: 8

PostPosted: Thu Aug 25, 2011 9:53 pm    Post subject: Reply with quote

I replaced the power board the other day and initially noticed no difference. I did some more testing today and found that the backlight is not functioning. I managed to navigate through the input menu using a flashlight and got both picture and sound. I swapped the old power board back in and got nothing again. I'm starting to believe this thing may have taken a power surge and fried some ic's. The tv also has two boards labeled master and slave. I'm assuming these are the inverter boards. They both have 24v coming in, but I haven't checked for outputs. What should I be seeing on the output side if they are working correctly and does anyone even sell backlights if that's what the problem turns out to be?
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