Entertainment Center: TVs, Stereos, VCRs and DVDs - GOLDSTAR CIT-9508 Brightness Control
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KIRK2
09-14-02, 05:14 PM
My Goldstar Colour TV (CIT-9508) has developed a problem with the brightness control. The picture is perfect except that it is about half the brightness of before. Using the remote control you can turn it up to about half the brightness of before, but it will not turn up sufficiently to be able to see the picture properly. This means that you can only watch programs that are bright scenes such as golf, football. If I turn the colour up & contrast, it makes things a little clearer.
Although I have the gear to make new circuit boards, and have had years of experience in making electronic projects, I don't have a service manual or circuit diagram for the CIT-9508. I think the brightness, volume, contrast etc is probably handled by a single chip which may have replaced the old potentiometer approach. From what I have read, these chips basicly receive a negative or positive pulse to turn the resistance up or down. However, the problem could be e.g. a transistor connected to the output from the chip. It is curious that the remote control still allows me to turn the brightness up & down to about half its old self. It's almost as if a buffering transistor (or whatever) is not amplifying the output which controls the brightness of the picture.
I had problems with the set about 2 years ago with dry joints, and had to resolder all the joints. This isn't the problem I have now.
Any of you Guys experienced a similar problem? I need to know how to fix the circuitry which controls the brightness. If I can turn the brightness up to half the level of before, it must be possible to fix it so that I can see a fully bright picture. The fact that the remote still has the ability to operate the up down brightness but only so far, suggests something, perhaps a transistor is not biasing up/amplifying the output from the chip. Unfortunately, I don't have a circuit diagram etc.
Any ideas?
Would appreciate any fix-it comments or info on the brightness control circuitry of this set (GOLDSTAR CIT - 9508). :confused:
Although I have the gear to make new circuit boards, and have had years of experience in making electronic projects, I don't have a service manual or circuit diagram for the CIT-9508. I think the brightness, volume, contrast etc is probably handled by a single chip which may have replaced the old potentiometer approach. From what I have read, these chips basicly receive a negative or positive pulse to turn the resistance up or down. However, the problem could be e.g. a transistor connected to the output from the chip. It is curious that the remote control still allows me to turn the brightness up & down to about half its old self. It's almost as if a buffering transistor (or whatever) is not amplifying the output which controls the brightness of the picture.
I had problems with the set about 2 years ago with dry joints, and had to resolder all the joints. This isn't the problem I have now.
Any of you Guys experienced a similar problem? I need to know how to fix the circuitry which controls the brightness. If I can turn the brightness up to half the level of before, it must be possible to fix it so that I can see a fully bright picture. The fact that the remote still has the ability to operate the up down brightness but only so far, suggests something, perhaps a transistor is not biasing up/amplifying the output from the chip. Unfortunately, I don't have a circuit diagram etc.
Any ideas?
Would appreciate any fix-it comments or info on the brightness control circuitry of this set (GOLDSTAR CIT - 9508). :confused:
FREDDYG_001
09-16-02, 09:54 AM
KIRK2, Whats the date of manufacture on that television?
Fred:)
Fred:)
Charles Peterso
09-16-02, 11:40 AM
I am having the exact same problem with my 46 inch ZENITH(PVR4663DT) PROJECTION TV. If you receive a answer that you think would help in my case please advise.
Thank you.:confused:
Thank you.:confused:
KIRK2
09-16-02, 04:26 PM
I can't find the exact year of manufacture for the Goldstar, but it was certainly before the Gulf War because I watched it on this set. Probably 2 years or slightly more before the Gulf War. This would make the set around 1994 or thereabouts.
It's nicely laid out inside the case. Remote control/Switch & manual adjustments at front of case feeding back to a small PCB which has a large chip SAA 1293 -02 ITT(Germany) on it, crystal, about half a dozen small transistors (not TO3 or anything). I think the main chip is a collection of simulated pots. When it receives an input from the wired manual controls at the front, I think it uses the crystal to pulse the brightness, volume etc up or down according to "0" or "1".
The main & only other PCB inside the TV (excluding the switch assembly on the front of the case) contains the high voltage transformer, video handling, tuner etc. This board doesn't appear to control the brightness. It does however have pcb pots for vertical hold, horizontal etc.
I think the smaller PCB with the SAA 1293 chip is the main controller. Unfortunately, I don't have a service manual or any data for the chip, so its difficult to figure out which pins do what.
I'm not convinced that the problem is with the chip itself (re brightness). The chip is still responding to the remote control & manual brightness control. It still turns the brightness up & down. It just doesn't turn it up far enough. Almost as if a transistor is failing to amplify the signal.
If you can find out anything about the brightness control on these sets, I would be most grateful. It really is a superb set. Almost a modular/blox design, the way the circuitry is laid out. Not a bit like some other sets which have everything just muddled together on one PCB. I'm sure the key to the problem is the smaller board with the SAA 1293 chip on it. Maybe some one has the pinouts for the chip? Then I could follow the inputs & outputs. :(
It's nicely laid out inside the case. Remote control/Switch & manual adjustments at front of case feeding back to a small PCB which has a large chip SAA 1293 -02 ITT(Germany) on it, crystal, about half a dozen small transistors (not TO3 or anything). I think the main chip is a collection of simulated pots. When it receives an input from the wired manual controls at the front, I think it uses the crystal to pulse the brightness, volume etc up or down according to "0" or "1".
The main & only other PCB inside the TV (excluding the switch assembly on the front of the case) contains the high voltage transformer, video handling, tuner etc. This board doesn't appear to control the brightness. It does however have pcb pots for vertical hold, horizontal etc.
I think the smaller PCB with the SAA 1293 chip is the main controller. Unfortunately, I don't have a service manual or any data for the chip, so its difficult to figure out which pins do what.
I'm not convinced that the problem is with the chip itself (re brightness). The chip is still responding to the remote control & manual brightness control. It still turns the brightness up & down. It just doesn't turn it up far enough. Almost as if a transistor is failing to amplify the signal.
If you can find out anything about the brightness control on these sets, I would be most grateful. It really is a superb set. Almost a modular/blox design, the way the circuitry is laid out. Not a bit like some other sets which have everything just muddled together on one PCB. I'm sure the key to the problem is the smaller board with the SAA 1293 chip on it. Maybe some one has the pinouts for the chip? Then I could follow the inputs & outputs. :(