A 21” GoldStar CRT TV set was brought to my shop with the problem of a dead set and the stand by LED was continually flashing on the set.

As always, checking for burnt and loose connections joints on the PC board and found none. There were some voltages coming out of the power supply to the HOT in the high tension section but dropping fast which indicated a power supply problem. I traced the problem backwards to the secondary power supply output and it showed the same problem. This assured me that there is a problem in the power supply section.

Upon fast scanning of the components in the power section, I noticed the power supply IC STRS5707 was getting hot. The fuse was intact and all the components looked fine to me on my first scan. There was power reaching the STRS5707 but the output voltage was very little and this prompted me to conclude there was something wrong with the STRS5707 IC. I used the LOPT/FBT meter to check on the primary winding and it showed only 3 rings (LEDs on). This was another indication of a bad IC in the power section.

I removed the IC out from the PC board and compared its reading with the new one and sure enough, the IC was shorted but to my surprise, it did not blow the fuse on this set.  From my experience when an IC like this gets shorted, it will usually blow up something in its path. So I started checking the component around this IC and found that there was a transistor blown (Q810) and there was a Zener diode (ZD810) shorted as well. When both components were removed, I checked on the transformer primary winding again with the LOPT/FBT meter and this time it gave me full rings.  I was very happy to see such a result on the meter.

I replaced the IC, transistor and zener diode  with exact part number.  I did not turn the TV for one reason and that was because I was thinking there might be another shorted component in the set and by turning the set on, I might blow up the new components that I have just replaced. So, the light bulb trick was used. I put a 100 watt light bulb on the fuse connections and turn on the TV and guess what? The light bulb came on very bright then it became dim and that put a smile on my face because I knew once I replace the light bulb with the actual fuse, the set will work.  Lastly the bulb was replaced by the original fuse and with power on the TV set came back to life!

There was 129 volts reaching the HOT and I was very concerned about it. It was a 21” TV set and that voltage is too high comparing with the size of the set. I kept the TV on for more than two hours and kept a close eye on the HOT. I kept touching the transistor once in a while to make sure that it will not go too hot. You can only touch the HOT when the power is off.  The result was the HOT ran a little bit warm and this means it was a good sign. After done a research on this GoldStar TV model, 129 volts was a normal voltage.

About

10 years of practical electronics. owner and operator. I service the Bethlehem area in Palestine. I repair Xbox 360 and all play stations and modify their power supplies. also repair lcd and Plasma tv sets, and lcd computer monitors. I have a degree from Bob Jones University in general business and one year degree in Industrial electronics. a intensive course in Media. I also work as a camera and audio man as a free lancer. Also great experience in video editing and installing surround systems for home and movie theaters.

8 comments on “Repair A Dead GoldStar CRT TV Model # CF20F30

  1. ALLEN NARH AGORVOR says:

    NEEDS INSIGHT TO THE 100 WATTS LIGHT BULB TRICK

    1. Waleed says:

      the light bulb trick is very easy and very practical trick. the reason we use it especially when there is a big short in the equipment. when you install new parts in the equipment and there is still shorts in the equipment, this short might destory and blow up all the new parts you just installed. instead, you install a light bulb in the place of the fuse, and turn on the machine. if the light bulb shines bright and stays bright, that means, there is still short in the machine. but when the light shines bright then it dims (not bright) that means, it is ok to replace the fuse and turn on the machine for the short is goine. I hope this helps. you can write me more using my email address, wrishmawi@hotmail.com

      1. model Goldstar when i turn on power will on after 10 minutes. Where is the problem?

  2. Waleed says:

    sorry I did not answer your question sooner..I just saw it..
    the reason for this tv to start after 10 minutes of pushing power button on is due to some bad capacitors in the power section..mostly in the primary section and also you could check the secondary capacitors as well with ESR meter. I hope this help.

  3. jo bori says:

    Hi Sir Waleed. Thank you for sharing your knowledge and experiences.
    I am repairing my dead set JVC AV21BN19 crt tv and replaced the STRW5753A voltage regulator IC as I find it shorted. Then, I put a 100 watt light bulb in place of the fuse and powered on. The bulb stays bright so I thought there must still be some shorted components. I checked all the usual suspects like the main & secondary ecaps, HOT, 9 & 5 volts regulator IC, etc and they all seems okay. I've read somewhere that the light bub trick may not work on some TV because of the degaussing circuit. They said that you have to temporarily remove the degaussing coil if you will use the light bulb trick. Is it true? Is it safe to power the TV without the degaussing coil? Thank you in advance for your help.

    1. Humphrey says:

      Hi bori, Usually short in the secondary circuit does not cause the light bulb to be bright…actually the TV will appear dead. Short on the primary side is the one that causes the series bulb to be bright, again only component shorted directly across the main power will cause this symptoms…so you should concentrate on those components only…with regard to degaussing coil you should always disconnect it all the time when working on the TV…you don't need it unless you suspect it to be shorted/or the posistor…in fact degaussing coil is used to clean up the screen of any magnetic(earth) effect and is used for less than 3 seconds after you switch the TV on and then switched off courtesy of the posistor. Hope i have answered your question Bori
      Regards Humphrey

  4. Jean says:

    Hy Waleed,

    I have a Goldstar TV, I do not remember the model, but it has a PCA processor (works with a VS-068 B remote) ad I have the following problem: it powers on good, but after some time, after it warms up (and it has been a very hot summer) I start noticing a strange thing when I change channels: it has a certain "delay" before it "locks" itself to the frequency of the new channel (just like when you search for a channel and there is that sequence before it locks itself perfectly and the image is black and white). After a while, it does not "lock" at all on the channel when I browse the list, it displays an unsynchronysed black and white image. If I turn it off and come back 30 minutes later it works well. I suspect there are some capacitors which need to be changed, but I have to pin point the problem exactly. Can you help me?

    Best regards,
    Jean

  5. menx says:

    strs6707 is not compatible with strs5707..

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