VCR Won't Power On


  #1  
Old 03-11-05, 10:50 AM
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VCR Won't Power On

Hello,

I have a VCR that acts like it isn't getting power. There clock won't display, the power button doesn't evoke the slightest response, and the tape loader won't respond to a tape when inserted part-way. It's as if the machine is unplugged; however, it is not.

I opened the case and found that the AC circuitry is enclosed in a protective cage. I opened that and started prodding around with a volt meter. Without a schematic and without remembering the color codes on resistors, I can't tell you if any of the readings are what they should be, but they seem fairly normal. The fuse is solid and has a 0V potential across it, nothing is charred or melted, ground is somewhere between the neutral and hot terminals, there's a 11V difference between the middle of transformer and ground, about 7V between the transformer and each AC terminal, etc. The power circuitry makes a quiet buzz that varies from time to time. Sometimes it's a high frequency, sometimes it's lower -- not in pitch, but in oscillation...like I'm hearing something buzzing at 60 Hz, but then slowing down periodically.

Without removing the tape mechanics and pulling the main board out of the case completely, I can't tell where the power "lines" leave the protective cage to power various parts of the unit. I guess the next step might be to do this and see if power is going anywhere.

In the mean time, can anyone tell what the likely culprit is? Dead transformer? Blown capacitor? Paperclip shorting something under the main board?

Thanks!
 
  #2  
Old 03-11-05, 11:06 AM
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Hi
might be cheapper to buy a new one than have it repair.

cheers

pg
 
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Old 03-11-05, 11:21 AM
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Where's the fun in that? I posted to a do-it-yourself forum for a reason
 
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Old 03-11-05, 03:38 PM
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Not a VCR expert, but

I think that VCR's like computers, have multiple voltages inside. It sounds like the low voltage part might be missing. ( I want to say 5 volts and maybe 9 or 12 volts for the motors and stuff, but I'm not up on the newer VCR's.)

I'd check for power at the various IC's inside the VCR. It's also possible that some sort of safety ciruit isn't working and has shut down the VCR. (Or the main microprocessor is toast)

Please post back with brand, model, chassis, etc. I'm sure someone with more of a clue than me will add to the discussion.
 
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Old 03-18-05, 12:45 PM
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when you check the power supply, do you check it with your dvm from the bottom side of the the board? solder side? there you may find specific voltages printed on the board.
I had a vcr that squeld from a paper clip bridge across a supply voltage. removed the short, and the squiel stopped, but blew a fuse that looked like a transistor. found this by tracing voltage readings marked on the board. replaced fuse and eveything worked fine. that xformer in the power supply is a switched mode transformer, (dc to dc converter), and will squel if there is any bad caps in the the supply voltages. But try to get your 5volt supply going, cause if you're missing that nothing will work.
hope this helps, hobbs
 
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Old 04-28-05, 09:11 PM
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Wow...did I ever get sidetracked...

Here is the model information you requested. I've been carrying it around in my notebook for over a month.

RCA VR652HF

Snuffs, I have not yet checked voltages on the solder side. I was hoping to avoid that because it would involve removing a lot of mechanical stuff. I will if/when I have to, though. For now, I've been checking voltages on the part of the pins that are above the board, or on the coils of the transformer.

I'll follow some of your suggestions and see if I have any fuses disguised as transistors.

Thanks everyone
 
  #7  
Old 04-29-05, 03:54 AM
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Those fuses disguised as transistors are commonly called ic protectors. Check also that you haven't blown a voltage regulator, that is pretty common. Also, the power supply will most likely either have a bridge rectifier made of four discrete diodes or an IC version, make sure that they aren't fried. These can probably be checked easier on the top of the board rather than the solder side.

You may have to get the part number off of the ICs and then check the manufacturer's web site to make sure the input and output voltages are within spec. You can work forward or backward from there depending on what you find. I would feel pretty confident that you had narrowed the problem down to the proper area, you just need to find exactly what is wrong now.

I am not familiar with your model, but if you need more generic help let me know.
 
 

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