JVC HR-S7900U keeps blowing fuses, shorted?

[bap2012]

Long backstory/ramble: I got the VCR a couple years ago, apparently it had been hardly used by the original owner. Pristine condition. I had used it briefly when I got it, but my digitization project got put on hold for a while. Now, I pull it out again, get it plugged in, I see the screen turn on and display text as it does. I plug the SVid cable from my capture card into the VCR. Next thing I know, the VCR refuses to turn on. As far as I know, it failed in the time between me plugging it in and me plugging in the SVid output cable. I don't exactly suspect the capture card in causing this because I just got done capturing tons of 8mm tapes with the same card and SVid cable, and that was all done *after* this happened with the VCR. I Opened the VCR and fuse was dead (right by the mains voltage in). Figured it might've just been its time to go, it is over 20 years old after all. Got the closest rated fuses I could find that didn't exceed the original fuse's rating (original: 250v 1.25a, ones I got: 250v 1a) and put one in, turned the machine on, nothing. Try a few more times, still nothing, open it up again and see the new fuse now has a brown mark. The next fuse failed without a burn mark as I slowly gave the VCR voltage with a variac, but still failed. So obviously there is a short somewhere, and bad on me for trying the same thing multiple times and expecting different results. But before I waste money on more fuses, I want to actually figure out the problem.

So, for this model and similar models, what are common points of failure that might cause a short like this where the fuse keeps blowing? Without taking the whole thing apart, I don't see any suspect capacitors or anything like that. Which components should I hone in on for testing? I do have a multimeter.
I really don't have money to spend on an expensive fix or God forbid, another VCR. I am hoping it is a relatively simple component I can replace myself. Any pointers are much appreciated!

[radiokom]

Recap power supply. It is a cause of a problem 99%. Then try to switch on. If still does not work, find cause.
Probably PS took something with it when dying.

[latreche34]

Either shorted capacitors or a bad power regulator, Usually 3 legged but JVC used multiple legged packs in some models power supplies, check the service manual for your model.

[aramkolt]

My guess is most likely it is the full bridge rectifier which is a rectangular 4-diode containing package on the underside of the main board and is a surface mount component on these. If it saw very little use based on your description, the capacitors are most likely fine. Those also tend to fail open rather than short and usually won't blow fuses. I have seen some crappy brands of main filter cap and those can sometimes fail. If it is a light blue "Lelon" capacitor, it is much more likely to be problematic compared to those from Nichicon or Panasonic. It's also possible that the component on the heatsink could be shorted also, which is usually a switching mosfet or similar.

I do full refurbs of these machines as a service and have lots of parts units, so message me if you can't figure it out.

[bap2012]

Thank you all for the replies. I will probably fiddle with it some more either tonight or tomorrow.

Quote:

Originally Posted by radiokom

Recap power supply. It is a cause of a problem 99%. Then try to switch on. If still does not work, find cause.
Probably PS took something with it when dying.

I will try to do some testing on those once I take it apart fully

Quote:

Originally Posted by latreche34

Either shorted capacitors or a bad power regulator, Usually 3 legged but JVC used multiple legged packs in some models power supplies, check the service manual for your model.

Much appreciated, thanks for the manuals!

Quote:

Originally Posted by aramkolt

My guess is most likely it is the full bridge rectifier which is a rectangular 4-diode containing package on the underside of the main board and is a surface mount component on these. If it saw very little use based on your description, the capacitors are most likely fine. Those also tend to fail open rather than short and usually won't blow fuses. I have seen some crappy brands of main filter cap and those can sometimes fail. If it is a light blue "Lelon" capacitor, it is much more likely to be problematic compared to those from Nichicon or Panasonic. It's also possible that the component on the heatsink could be shorted also, which is usually a switching mosfet or similar.

I do full refurbs of these machines as a service and have lots of parts units, so message me if you can't figure it out.

Thank you for the input! As a general idea, how much would fixing this set me back? And is buying service parts from you a possibility, or is there anywhere else you recommend getting them?

[aramkolt]

Would depend on what part is bad as far as where I'd recommend getting parts, but for passive components like capacitors/diodes, I use mouser.com (Digikey is fine too) though since these machines were made a long time ago, they might not have the same regulators or full bridge rectifiers available. There likely are some newer compatible components, but I generally like to stick to the original part numbers usually from parts machines. You'll have to let me know what ends up being bad and I can double check if I have those parts or not.