Power supplies are usually pretty simple to fix, if you have the right equipment. Take it to a tech school and see if any of the 2nd year students would be willing to have a look at it for $10.
It’s a switched mode power supply. These normally don’t employ linear regulators, since the regulations in switchers is accomplished by feedback from an error amplifier circuit. That part you mention is most likely the chopper transistor, which chops up the the rectified AC mains input at about 10 -20 kHz.
Wow, thanks for the replies (again) guys. Thanks for not
saying “why don’t you just get it fixed”…or “just ditch it and buy
a new one”. I find this pretty interesting, so I’m curious to see if
I can actually fix it 
Please check out the last picture on this page again. I labeled
one of the other pictures with some of the names I was given to
make sure I’m looking at the right parts. The part that I labeled
the “linear regulator”…I guess that could also be the chopper
transistor, according to Q.E.D. Either way, I guess I have to
replace it, right?
I’ll try to get closer pictures as you requested, along with some
numbers. Any idea where I can get some of these parts? (like
the two that you suggested changing?) Is RadioShack a good
bet, or is that not specific-enough of a store?
http://www.angelfire.com/nj4/cpgoose/VCR/pix.html
THANKS!
Q.E.D. are you sure? Because looking at the components, it appears that all the parts for a diode rectifier->linear regulator are there, and there’s absolutely none of the kind of shielding that a switched power supply would need, especially when it operates at frequencies near the horizontal scan rate, and can give off harmonics well into UHF. And that flange mount package with three pins looks like a linear regulator, while I would expect a switching power supply to come in a potted module or a little metal case or something.
The part number from that package would clear up any confusion.
Yes, cpgoose those are all the parts I called out last night.
I also see another transistor or something in a similar package to the linear regulator, laying down on the board, to the left of the transformer… get that part number, too, if you can. And those are two more caps, one in a small silver can with blue wrapping and the other in a reddish ceramic “lozenge.” Treat them with respect, they can store charge and give you a nice burn if you discharge them with a finger or something.
If you can make photos close enough so we can read the letters on the components, and another so we can see the backside and look for scorching, that would help a lot.
Good Luck and don’t cross the beams!
Er… I mean, don’t touch the heads!
Oh, and for parts, try Radio Snack first, since you can walk in. Or you can order from Newark Electronics or DigiKey. The latter will gladly do the onesie-twosie quantities you will need.
Or, if you aren’t afraid of a little social engineering, research the part manufacturer, call one of their dealers, and ask for samples. Pretend you’re a business. They will usually send you quantities of one or two for free.
Thank you again bughunter…I will definitely try to get you more pictures tonight. Hopefully my camera will get clearer pictures. I’ll try to get some numbers, too.
When you say to get pictures of the other side, too, then you mean to just take out the couple of screws holding everything to the plastic base, and then take it out and flip it over, right?
Pretty sure. That transformer is too small to operate at 60 Hz and provide enough power to run the VCR. And those electrolytic caps are too small to provide effective ripple suppresion at 60 Hz, either, assuming they’re rated at 16 WVDC. Cpgoose, see if you can read the numbers on it and post them here. That should identify it, if it’s not labelled with proprietary numbers.
Oh and that blue disk you have labelled as a capacitor isn’t, cpgoose. It’s a device called an MOV (metal oxide varistor). It’s used to protect against voltage surges.
I’m still skeptical, Q.E.D., because rather than design and layout their own switching supply, most consumer electronics makers will just buy a module from a power supply OEM who can pass on their economy of scale, and package that. Plus, there’s no shielding to make the supply comply with FCC RF emission regulations for consumer electronics.
And VCRs really don’t need that much power. Those components are certainly big enough for either circuit.
Maybe, but if it is a linear supply, the layout is odd. The “regulator” is on what would normally be the primary side of the transformer. The layout is much more in keeping with a switcher.
I started taking some pics last night, and the numbers on the board are even coming out pretty good. I didn’t have enough time to take out the board, and get pictures of the other side, so I’ll finish that in a bit. Hopefully the numbers will help resolve this.
Yes, I noticed this, too.
cpgoose, just to be clear - the numbers we want are on the components. The numbers on the board itself may be useful later, but right now they’re just gravy.
The backside photos are mainly so we can look for obvious signs of arcing or other overvoltage damage, but you can probably spot that yourself.
Also, **Q.E.D.[\b] if that MOV is there to provide surge protection, does it fail open or short?
MOVs fail open (or rather, very very high resistance), once they’ve absorbed their maximum surge energy dissipation. Since they are parallel to the circuit, this effectively removes them from the circuit, which should continue to operate normally, until the next surge takes out something more important.
Ok, I took some pictures, hopefully they’ll be helpful to you. I
tried to get a bunch of closeups of the parts we’re talking about.
Let me know if you would like specific pictures or numbers that I
might have missed. I was unable to get the board out, though,
to flip it over and take pictures. I removed 5 screws (see
the “Whole board” shot below for the red circles where I
removed the screws), but I was still unable to pull or slide the
board out. Any hints? See the links below:
Thanks!!!
Diode Bridge
Transformer
Linear Regulator
Lozenge 1
Lozenge 2
Whole Board
Having been in the industry … I think you can order the parts from JVC direct or through a local authorized service center.
I don’t know if their service manuals are on line, though.
This s really amusing, watching this play out online. I never actually did this level of work (just belt replacement, head cleaning, testing and tons of warranty paperwork) but it’s fascinating.
Wow, I didn’t realize others were really interested
These guys have been very helpful, though…I’m so
curious to see if this will work (me trying to fix it). I hope so!
I don’t want to out a damper on the DIY party, but new VCRs loaded with features can be had for 50 - 70. on sale. Just get a new one. The PITA to service and the parts cost is not going to make repairing it make economic or practical sense.
OK, well, Q.E.D. was right about the switched-mode supply.
The “regulator” is labeled with pins “G, S, and D.” That means it’s a field effect transistor (FET), not a regulator. Get us a photo of the front face, with all the numbers legible, and we can ID it better.
As for the board, there clearly must be more screws holding the board to the case. We can’t see them in that photo. Keep Looking. Try taking off the tape transport deck (the big silver assembly holding all the moving parts) and looking under that. And take photos of things before you take them apart so you can see how they go back together.
And astro is right. You can certainly get a working replacement for less than $50 if you wanted to. Look in thrift stores and salvation army stores… with the sheer numbers of VCRs sold in the US over the past 20 years, there should be something you can afford available used.
Here are some numbers from these parts:
- Diode Bridge
- Linear Regulator (well, the thing that was initially called the LR)
If all you are looking for is getting the VCR to work again then you are right but I attempt things like this all the time even if it costs me in time and money because of what I learn and that is what this board is about.
having said that I will say that I have had zero luck repairing switching power supplies and I have several which I have attempted and put away. It is just not worth the effort as you can get a new one for very little. But the fact is that I have learnt a lot about switching power supplies this way. The main thing I have learnt is that it is not worth trying to repair them. First case: The two BUV48 switching transistors are shot. I replace them. The replacements are promptly shot. Further inspection reveals the controller IC UC3842 is shot too. I now replace the two switching transistors and the IC. I soon have two more transistors and an IC shot. This goes on for several components. I try to put some protections in place but it is very difficult. The switching transistors rely on the controller to limit their time on. everything individually seems to be working but the feedback loop as a whole does not. It gave me hours of amusement but I never did manage to repair it. Which is just as well because it was a stand-alone unit and you could buy a better, more modern and efficient, one for under $30. But it was a lot of fun.
Some links:
http://www.smpstech.com/tutorial/t00con.htm
http://www.smpstech.com/websites.htm
I had a good PDF document about repairing switching power supplies but I cannot find it now. I found it online so a search should find it.