JVC HR-S7955 not powering on since power cut/surge

Thread Starter

Lee Mourant

Joined Sep 4, 2018
12
2 of my JVC VCR's no longer power on since we had a power cut yesterday. There must have been some sort of power surge which as killed them.

Can anyone suggest any things to check? I have checked the fuse inside the VCR and that is OK, in fact my voltage stick detects voltage all round the circuit board.

I have checked for voltage across the fuse and there is nothing.
 

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I have checked for voltage across the fuse and there is nothing.
It doesn't make sense to check the voltage across a fuse. The right way is to check for continuity across it. Sometimes by visual inspection you can notice if it's blown up. Of course, if they are glass fuses.

in fact my voltage stick detects voltage all round the circuit board.
Where are you taking measurements? How much voltage do you see?
 

Thread Starter

Lee Mourant

Joined Sep 4, 2018
12
It doesn't make sense to check the voltage across a fuse. The right way is to check for continuity across it. Sometimes by visual inspection you can notice if it's blown up. Of course, if they are glass fuses.



Where are you taking measurements? How much voltage do you see?
The fuse has not blown, should there be power across the fuse? (I have attached a picture). No obvious signs of anything blown, or smell.
 

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If you try to measure voltage across a good fuse, you will read 0V because it's like a shorted path. You rather measure current, but it's impractical in this case, as you simply can check fuse continuity. I suggest to check the device pointed out below in red circle

 

Thread Starter

Lee Mourant

Joined Sep 4, 2018
12
If you try to measure voltage across a good fuse, you will read 0V because it's like a shorted path. You rather measure current, but it's impractical in this case, as you simply can check fuse continuity. I suggest to check the device pointed out below in red circle

Thank you for your advice, much appreciated. What is the device you circled? Is it just a visual inspection I need to do?
 

LesJones

Joined Jan 8, 2017
4,174
I think this is a link to the datasheet on the TO220 device circled. It's specifications seem to fit the job of the main switching device in a switchmode power supply. If the cause of the fault was a high voltage transient then I would have expected this device to have failed short circuit and taken out the fuse. As you have now told us that you are in the UK it is probably fitted with a 13 amp plug. If so then it will have a fuse in it. Have you checked this fuse aswell as the one on the PC ? I suggest that you try to find a schematic of the unit and post a link to it so we have a better chance at working out what is causing the problem. My first step would be check if you have about 340 volts DC on the main reservoir capacitor. As you do not seem to know much about electricity I don't think iit is safe for you to do that test.

EDIT. Forget testing the fuse in the plug as I have noticed that you have mains voltage at the input to the board.

Les.
 
Last edited:

Thread Starter

Lee Mourant

Joined Sep 4, 2018
12
I think this is a link to the datasheet on the TO220 device circled. It's specifications seem to fit the job of the main switching device in a switchmode power supply. If the cause of the fault was a high voltage transient then I would have expected this device to have failed short circuit and taken out the fuse. As you have now told us that you are in the UK it is probably fitted with a 13 amp plug. If so then it will have a fuse in it. Have you checked this fuse aswell as the one on the PC ? I suggest that you try to find a schematic of the unit and post a link to it so we have a better chance at working out what is causing the problem. My first step would be check if you have about 340 volts DC on the main reservoir capacitor. As you do not seem to know much about electricity I don't think iit is safe for you to do that test.

Les.
Thanks Les. I know very little about electric and circuit boards. I have checked the fuse on the PCB and that is OK.

It is so annoying as both of my JVC VCR's died when we had this power cut over the weekend.

I found a service manual (attached) not sure if this is any use for what I am trying to identify.
 

Attachments

I took the following circuit fragment from the document you attached. Another potential failure can be the bridge rectifier. I suggest you to google how to check those components using a multimeter so you can find a more ilustrated information. Maybe YouTube, or some tutorial over there which provides pictures/videos. Take those measurements while the device is disconnected from mains.

 

Dodgydave

Joined Jun 22, 2012
11,285
2 of my JVC VCR's no longer power on since we had a power cut yesterday. There must have been some sort of power surge which as killed them.

Can anyone suggest any things to check? I have checked the fuse inside the VCR and that is OK, in fact my voltage stick detects voltage all round the circuit board.

I have checked for voltage across the fuse and there is nothing.
From your service manual, the output voltages are 5V, 5.8V, 12V,.

The input voltage will be 350V dc across the large capacitor C5006..

Incidently who the hell uses VCR's these days!!
 

LesJones

Joined Jan 8, 2017
4,174
Looking at the schematic it looks like there is a +48 volt output from the power supply section even when it is in standby mode. It should be reasonably safe for you to test if this voltage is present. Looking at the schematic it looks like there are left and right audio out and video out to what are probably phono (Sometimes called RCA) connectors. Connect the black test lead from your meter to the outer metal part of one of these. (This will be the system ground.) with the meter set to the 200 volt DC range touch the red meter test lead to the positive of D5201. BE VERY CARFUL NOT TO SHORT IT TO ANYTHING ELSE WITH THE TEST PROBE. From the board layout picture it looks to be close the high frequency transformer in the power supply section. It is on the opposite side of the transformer to the mains input area. In the picture in post #6 it should be near the bottom right hand corner of the transformer. If the power supply section is working you should get a reading of about 48 volts.

Les.
 

Thread Starter

Lee Mourant

Joined Sep 4, 2018
12
Looking at the schematic it looks like there is a +48 volt output from the power supply section even when it is in standby mode. It should be reasonably safe for you to test if this voltage is present. Looking at the schematic it looks like there are left and right audio out and video out to what are probably phono (Sometimes called RCA) connectors. Connect the black test lead from your meter to the outer metal part of one of these. (This will be the system ground.) with the meter set to the 200 volt DC range touch the red meter test lead to the positive of D5201. BE VERY CARFUL NOT TO SHORT IT TO ANYTHING ELSE WITH THE TEST PROBE. From the board layout picture it looks to be close the high frequency transformer in the power supply section. It is on the opposite side of the transformer to the mains input area. In the picture in post #6 it should be near the bottom right hand corner of the transformer. If the power supply section is working you should get a reading of about 48 volts.

Les.
Thanks again Les. I will try this tomorrow and report back.
 

Thread Starter

Lee Mourant

Joined Sep 4, 2018
12
Looking at the schematic it looks like there is a +48 volt output from the power supply section even when it is in standby mode. It should be reasonably safe for you to test if this voltage is present. Looking at the schematic it looks like there are left and right audio out and video out to what are probably phono (Sometimes called RCA) connectors. Connect the black test lead from your meter to the outer metal part of one of these. (This will be the system ground.) with the meter set to the 200 volt DC range touch the red meter test lead to the positive of D5201. BE VERY CARFUL NOT TO SHORT IT TO ANYTHING ELSE WITH THE TEST PROBE. From the board layout picture it looks to be close the high frequency transformer in the power supply section. It is on the opposite side of the transformer to the mains input area. In the picture in post #6 it should be near the bottom right hand corner of the transformer. If the power supply section is working you should get a reading of about 48 volts.

Les.
I am struggling to D5201, can you point me in the right direction? I can see D5206 etc but not D5201.
 
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