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#1
02-06-2022, 01:13 PM
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So what is the "Panasonic power supply issue"?
Eveywhere I look I see either people saying that VCRs suffer from it or people saying I have a VCR that suffers from it, but what IS the problem? Is it the capacitors? Diodes? bad mains?
I bit the bullet and got the same unit as the one that my father had in '84 to hopefully read better all the tapes that have been saved in collection. Fuses blow right away, but before I start desoldering the metal protection cage, I want to know if there's any hope SDC12101.jpg SDC12102.jpg 
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#2
02-06-2022, 08:52 PM
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Q4 is probably shorted, and maybe the driver for Q4, also check any Zener diodes tied to a voltage output check all capacitors with an ESR meter and replace as indicated. Then plug in to AC with a 40 Watt light bulb (incandescent) in series to keep from damaging any more parts. If it lights up full bright you still have a short. If it lights up a little and immediately fades out then it's probably fixed. That's how I recall fixing many of those back in the day but it's been almost 20 years.
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#3
02-07-2022, 10:03 AM
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Thanks Ed. Looking at Q4 its a 2SC3170. Doesnt seem to be made anymore but there are a few old ones up on ebay. do you know if there's an equivalent?
Great idea on the bulb tester, made one of those many many years ago i'll have to look for it or just make a new one. Are diodes identifiable without a schematic? SAMS has one for $22 but id rather not add any extra expense to this project that may end up as a dud anyways.
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#4
02-07-2022, 10:12 AM
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Is Q4 shorted?
You should be able to tell if there is a shorted Zener by checking the outputs of the power supply for a short to ground. Without a schematic might take some guess work. They typically put a Zener slightly higher rated than the normal voltage on one of he outputs to act as a clamp in case of excess voltage to intentionally blow the fuse and protect the electronics from damage. Was the original fuse blackened? Might have been hit with a power surge.
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#5
02-07-2022, 10:23 AM
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I havent checked any components yet, just getting ready to. I dont have and ESR handy so going to borrow one from a friend. Still need to desolder the entire metal shield off the bottom, not a fun task.
The original fuse was black as night, looked like it exploded inside the glass. When I replaced with my own fuse, it blew normally. Sounds like a power surge initially put this thing out of commission. Otherwise the unit seems to be intact, except it sounds like theres a a shred of tape thats stuck inside the tape head cylinder (inside that little 1/32" gap between the top and bottom of the head. when i spin the head i can feel resistance and a crinkling sound that sounds like tape. Tried to unscrew the two screws on the head to remove it but no luck, Im guess its soldered in somewhere. Visual inspection of the heads look intact, im just hoping the thin copper wire inside didnt break. otherwise this unit is permanently dead.
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#6
02-07-2022, 10:31 AM
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If it doesn't have visible wires from the upper cylinder like many older VCRs had, then it has pins that come up from the rotary transformer through the bottom of the upper cylinder and are soldered to the board on top. You would have to desolder those pins to remove the upper cylinder and check for something inside.
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#7
02-07-2022, 11:28 AM
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#8
02-07-2022, 11:43 AM
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No not all 16 just the 8 that go to the rotary transformer. The other ones go to the heads. Don't mess with those. Easier to show you see picture.
I would also inspect the heads very closely for any damage. I used a 10X loupe for that. Last edited by Ed in Tx; 02-07-2022 at 11:46 AM.
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#9
02-08-2022, 10:33 PM
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Thanks Ed. Started doing it but was having some soldering braid trouble (will get back to it)
I was able to get the metal shield removed off the power circuit, removed Q4 and Im getting a voltage when testing E to B (which should be an OL reading) so i'm guessing its no good. (NPN with order B-C-E) Q1 and Q2 checked out okay Last edited by starbond; 02-09-2022 at 12:04 AM.
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#10
02-09-2022, 02:09 AM
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I actually have a GE Badged Panasonic 4-Head Linear Stereo VCR from 1987 that came from my great-grandfather's house when they were cleaning it out to get ready to sell it and it also randomly developed a power supply issue one day (and it had been working perfectly up until the middle of last year and I got it around October of 2020 and then suddenly one day the VCR just died, (no front panel display or anything.)
When I opened it up, the fuse was blown and it was blown the same way as the OP's VCR's fuse was blown, which was pitch black glass like it had blown really hard from some sort of hard surge of some sort. I had attempted to check capacitors and transistors on the power supply board and I only saw one capacitor that looked bulged and I replaced it and the VCR didn't come back to life, it still was blowing fuses. 
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#11
02-09-2022, 08:31 AM
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Quote:
 So far, I can say Q4 is definitely one of the issues. Still need to check diodes and capacitorsI pulled C5 which is a 120uf 200V cap, and tested with my DMM.. in capacitance mode it read 125uf which is fine, in resistance mode I got 18MOhms, when hooked up to 9v battery and measured I was getting 9V so i think this one is okay. None of the caps looked bulged so I can either test 1 by 1 or replace them all as a precaution Last edited by starbond; 02-09-2022 at 08:47 AM.
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#12
02-09-2022, 10:11 AM
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Your vintage did not have the "under spec'd" capacitors which plagued the industry years later.. If one failed, it's because it's nearly 40 years old, dried out and opened. That will not cause fuses to blow.You are looking in the correct area which would be with the circuitry on the primary side of the transformer for shorted components, Q4 and the associated diodes.
In the 30 years servicing consumer, industrial and broadcast VTR's, I have never seen a piece of recording tape find its way between the upper and lower drum. Most likely, the bearings are shot in the head motor. That being the case, the VTR is junk. That is the most expensive part in the unit and is long discontinued anyway.. If you attempt to remove the upper drum, make very sure you have the leads totally desoldered or you will break a pin and the head motor is ruined. The upper drum(heads) is pressed onto the lower unit, so it may take some patience wiggling it off. They can be difficult sometimes removing it. I don't mean to be pessimistic but I can see this restoration being a money pit and you end up being very disapointed. I have bought working units from the Goodwill for $5-10 each. I have six spare decks from the Goodwill to ensure I have something to play the tapes in my very large library. I have seen it many times and for what you will invest in your 1984 vintage can amount to a lot. Last edited by djski; 02-09-2022 at 10:27 AM.
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#13
02-11-2022, 05:24 PM
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Quote:
its not a blown head. But i have only put $10 into this unit at this point so if it turns out the head it dead then at least it was a learning experience how to troubleshoot a power supply IMG_2470.jpg
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#14
02-11-2022, 10:24 PM
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Quote:
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#15
02-14-2022, 05:48 PM
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Quote:
Q4 arrived today, put it in the circuit and it STILL blows.  I tested diodes 1-5 on the circuit as well as Q1 and q2 which appeared to be still in spec D1 is a bridge rectifier so its probably fine D2 reads .5V forwards and OL reverse D3 reads .6V forwards and 2V reverse D4 reads .6V forwards and 2V reverse D5 reads .6V forwards and 1.8V reverse these were tested in circuit as the leads are so short, if i removed them i dont think id be able to get it back in. Last edited by starbond; 02-14-2022 at 06:24 PM.
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