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Rear Projection won't power on - 50FX30B
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PostPosted: Wed Jul 13, 2005 8:35 pm    Post subject: Re: Dead Hitachi Reply with quote
Stephen wrote:
You should find the line driver, usualy located next to the HT transformer on a heat sink,check to see if shorted by disconecting the collector. (Hopefuly you know how to check a Transistor). I sound to me this could be the problem, if the driver is not shorted check if you have line voltage on the collector of the driver should be +/- 115 volts d.c. if missing prehaps theres a problem in the supply which I doubt as the set is going into protection usualy a result of a short in the line.


I don't mean to appear dense but I'm not sure which is the HT Transformer, can you perhaps tell me where it is located on the board? Or maybe give me some part numbers? I see perhaps 3 or more transformers on the board....is it located near the power supply or near the lEDs? Thanks again for all the help.
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absorbentgnome



Joined: 30 May 2005
Posts: 51
Location: Cardiff, UK
PostPosted: Thu Jul 14, 2005 1:08 pm    Post subject: Reply with quote
The HT (high-tension) transformer is the transformer usually referred to as the flyback transformer or LOPT/LOPTx (line-output transformer). It's main purpose is to create the EHT (extra-high tension) voltage of ~24kV required for the picture tube. You can identify the LOPT/flyback/HT transformer by the fact that it is usually situated on the corner of the board, it is tubular in shape and it has a thick red wire coming out of the top leading to a rubber insulated cap where the wire clips onto the tube.

Usually, nearby is an aluminium heatsink with the LOPTr (line-output transistor) mounted on it. This is the HOT, line-driver, whatever.

You can test the HOT using a cheap digital multimeter, that measures the forward voltage drop (should be around 500mV) across each junction. Beware however that some HOTs have an internal resistor and/or freewheeling diode that can make it look like its knackered. Obtain the datasheet for your component to identify its type, and test accordingly.

If it is ok, then you should test the SMPSU rectifier diodes for shorts, by substitution and replacement.

If you want to repair the set read Sam's TV FAQ (Google!) and Notes on SMPSUs. Get some desolder wick as well. If u don't wan't to learn and risk knackering your set even more then take it to a repair shop.
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Unlucky320



Joined: 14 Jul 2005
Posts: 4
PostPosted: Fri Jul 15, 2005 12:34 am    Post subject: Reply with quote
absorbentgnome wrote:
The HT (high-tension) transformer is the transformer usually referred to as the flyback transformer or LOPT/LOPTx (line-output transformer). It's main purpose is to create the EHT (extra-high tension) voltage of ~24kV required for the picture tube. You can identify the LOPT/flyback/HT transformer by the fact that it is usually situated on the corner of the board, it is tubular in shape and it has a thick red wire coming out of the top leading to a rubber insulated cap where the wire clips onto the tube.

Usually, nearby is an aluminium heatsink with the LOPTr (line-output transistor) mounted on it. This is the HOT, line-driver, whatever.

You can test the HOT using a cheap digital multimeter, that measures the forward voltage drop (should be around 500mV) across each junction. Beware however that some HOTs have an internal resistor and/or freewheeling diode that can make it look like its knackered. Obtain the datasheet for your component to identify its type, and test accordingly.

If it is ok, then you should test the SMPSU rectifier diodes for shorts, by substitution and replacement.

If you want to repair the set read Sam's TV FAQ (Google!) and Notes on SMPSUs. Get some desolder wick as well. If u don't wan't to learn and risk knackering your set even more then take it to a repair shop.


Thanks for the help. At the risk of sounding even more dense than I did before...could you be a little more specific. I'm assuming you are referring to what I would call the high voltage transformer. I see several transistors around it, some on aluminium heatsinks. I don't suppose you could be more specific and tell me part numbers could you? (something like, you need to replace part number Q904 or something?) I just can't understand why only my red LED lights up....on all the other forums I found the green ones light up too. Thanks again for all help provided.
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Unlucky320



Joined: 14 Jul 2005
Posts: 4
PostPosted: Wed Jul 27, 2005 12:27 am    Post subject: Hitachi 50fx30b Reply with quote
Just wanted to let you know that we got the set working. Contacted Hitachi repairman and was told it was probably a cap or a regulator, replaced part # STRM-6511, the set came on and seems to be working fine. Thanks for all the help.
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KS



Joined: 12 May 2005
Posts: 3
PostPosted: Fri Aug 26, 2005 1:48 pm    Post subject: Reply with quote
Thanks for the update glad to hear it works now, 3 quick questions though:

1. What model of TV was yours I believe you had indicated it was a Hitachi 50fx30b, but I don't see that part number in the service manual (pdf).

2. Can you describe the part (STRM-6511), is there a number on or next to it on the board (the protection board on mine numbers them from I901 to I907)? All the searches I have done indicate this to be a semiconductor (I.C. probably a Voltage regulator @ less than $20) and which board is it on?

3. Where did you get the part from?


Maybe ther is some hope - Thanks again for the feedback.
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minnie



Joined: 18 Aug 2005
Posts: 2880
Location: Hell
PostPosted: Fri Aug 26, 2005 6:07 pm    Post subject: Reply with quote
Check F903.
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