Need repair advice for Hitachi CRT (chirping power supply)

[CubsWin]

My Hitachi 57F710S has been making a high-pitched noise for quite some time now. Some days are worse than others and sometimes it seems that I am the only person who can hear it. I finally decided to call a certified Hitachi service center and the technician came out to my house last week. Unfortunately, the technician was unable to hear the frequency that I was hearing, so it was difficult to diagnose the problem. When he pushed against the power supply heat sink, the pitch changed very slightly, so I told him what I heard and he suggested replacing the power supply board. I was able to pinpoint that the noise is definitely coming from the general area of the power supply and not the high voltage/flyback side. Has anyone else had a similar problem with vibrations/noises in the power supply, and how likely is it that replacing the board will solve the problem? Any advice would be appreciated. I don't mind spending $200 to fix the problem, but if I spend $200 and the noise is still there, I won't be very happy! Thanks!

 

[jayn_j]

My Hitachi 57F710S has been making a high-pitched noise for quite some time now. Some days are worse than others and sometimes it seems that I am the only person who can hear it. I finally decided to call a certified Hitachi service center and the technician came out to my house last week. Unfortunately, the technician was unable to hear the frequency that I was hearing, so it was difficult to diagnose the problem. When he pushed against the power supply heat sink, the pitch changed very slightly, so I told him what I heard and he suggested replacing the power supply board. I was able to pinpoint that the noise is definitely coming from the general area of the power supply and not the high voltage/flyback side. Has anyone else had a similar problem with vibrations/noises in the power supply, and how likely is it that replacing the board will solve the problem? Any advice would be appreciated. I don't mind spending $200 to fix the problem, but if I spend $200 and the noise is still there, I won't be very happy! Thanks!

These kind of noises are generally caused by a loose transformer winding, loose heatsinkl attachment or something else where magnetic fields cause a mechanical vibration.

My only problem is that you say it is very high pitch. The power supply is working at very low frequencies and resonances should be around 60 Hz, not the 20 kHz you are mentioning. That sort of frequency is generated by the horizontal sweep circuit, amplified and sent to the flyback. I would be looking at the sweep board, the HV amp or the flyback.

I could be wrong, but I don't think replacing the power supply will solve it.

 

[CubsWin]

My only problem is that you say it is very high pitch. The power supply is working at very low frequencies and resonances should be around 60 Hz, not the 20 kHz you are mentioning. That sort of frequency is generated by the horizontal sweep circuit, amplified and sent to the flyback. I would be looking at the sweep board, the HV amp or the flyback.

I wouldnt say that it is very high-pitched. but I'm not knowledgeable enough to say whether what I'm hearing is 60 Hz or 20 kHz. How would I determine or rule out whether the frequency is being generated by one of those other components? I should also clarify that the technician thought the frequency I heard was that of the voltage switching inside the power display.

 

[jayn_j]

I wouldnt say that it is very high-pitched. but I'm not knowledgeable enough to say whether what I'm hearing is 60 Hz or 20 kHz. How would I determine or rule out whether the frequency is being generated by one of those other components? I should also clarify that the technician thought the frequency I heard was that of the voltage switching inside the power display.

OK, that makes sense. A switching supply will operate at a few kHz which would give a sound around high C. Middle C is 440 Hz, and 60 Hz would be a bass type buzz. Could be the PS board, but I make no predictions without hearing and seeing it. Since the TV is working, I still stand by the fact that the problem is mechanical vibration and can probably be fixed with a spot of glue. However, unless you are trained, I am certainly not going to recommend poking on live circuits.

 

[CubsWin]

Since the TV is working, I still stand by the fact that the problem is mechanical vibration and can probably be fixed with a spot of glue.

I'm sure you are probably right and that's what I was hoping for, but since the technician couldn't hear the frequency I'm pretty much out of luck there. At this point, I could either try another technician, pay $200 to replace the board, or continue to attend loud concerts until I'm unable to hear the noise myself. Since the first option is going to cost me $80 just for someone to come out again, I'm thinking I might as well just get the board replaced and hope for the best.

 

[CubsWin]

I decided to replace the power supply and the technician came today to replace it. It didn't take him very long and he had the new power supply in and the TV running, then I paid and he left. I watched TV for a couple hours, then turned it off and left for the night. When I came back later in the evening and tried to turn the TV on, it wouldn't turn on. It would click, but not turn on. I unplugged the TV and plugged it back in and it just constantly clicks until I unplug it. I'm going to call the service center back in the morning, but they only do house calls on Wednesdays and Fridays so I'll be waiting awhile. Does anyone have any idea what might have happened?

 

[Ilya]

Could be a number of things, but I woldn't touch the TV set. Let the tech come back and fix it - it's his fault most likely.

 

[navychop]

Definitely.

How old is the set? How much more life left in the tubes? That might guide you on how much to spend on repairs.

 

[CubsWin]

The TV is about 4 years old. With a good optics cleaning, I was hoping to buy myself at least another 2-3 years before I need to upgrade.

 

[navychop]

Not that I'm knowledgeable, but I think a good TV should last at least the 7 years you mention. By then, the guns may have dimmed, and may not be available, at least not at any price you'd be willing to pay. Or may be going strong. And the other technologies are getting better and cheaper.

My 720p LCoS set is 4 years old. Still looks great. But I'm hearing that the optics package is no longer available, so I too may have an unpleasant surprise waiting for me.

Let's both run our sets into the ground before replacement!

Best of luck in repairs, and please report back.

 

[CubsWin]

The technician came out today and brought my original power supply with him. He tested a few other things first and didn't find any problems, so then he swapped the new power supply out and replaced it with my old one. The TV powered on normally and is working now. Apparently the brand new power supply was defective, so he is going to send it back for a replacement and my Hitachi lives to fight another day.

 

[bhelms]

?? A "ghost in the machine" ??

As technician over the years I have seen similar "repairs". When I was in the business independently I didn't have the heart to charge anyone for such a mystery job even when I had some time and materials into it. To our (tech's) credit, there are plenty of intermittent problems that take sheer luck vs. hard work and genius to solve, meaning that in spite of honest work and best attempts there are still those that escape us. Been there, done that...

Good result for you however. I hope the original problem you had doesn't return, and that you didn't have to pay too much for for what was, or was not, done...