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Old 15th Dec 2019, 9:19 pm   #1
MusicWorks
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Default PSU dead in VCR

Hi everyone,

After a grueling 8-hour overhaul of a high end VCR, which included recapping the entire PSU, disassembly to fit the new capstan motor, and cleaning/oiling of the mechanism, got it all working fine and while doing the final adjustment (5V DC voltage output) I shorted the +5 and +12V rails of the PSU, and it appears to be muted somehow -dead as a stone.

There are three test points in the PSU: TP1 (12V), TP2 (5V) and TP3 GND. I was so exhausted I shorted TP1 and TP2, in 1 or 2 second mains was disconnected.

Please could you help me find the fault? I am really tired, weary and dissapointed. Almost had a heart attack after all the painstaking work to get the mechanical working perfect.

Actual pictures of the PSU:

****************/album/hNYOrF

Will post the schematic shortly, as soon as I can post the PDF of the service manual.

Many thanks!
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Old 15th Dec 2019, 11:00 pm   #2
toshiba tony
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Default Re: PSU dead in VCR

Go on, make or at the very least model number!
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Old 16th Dec 2019, 2:00 am   #3
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Default Re: PSU dead in VCR

Looks a little JVC-ish, but your guess is as good as mine! Anyway, have a nose round for anything that resembles a two-legged transistor, labelled 'ICP'. These are Integrated Circuit Protectors, and you will find one or more open circuit.

Just be sure to replace with the same type, as they are safety-critical components.
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Old 16th Dec 2019, 10:59 am   #4
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Default Re: PSU dead in VCR

That looks so familiar but I've failed at the 'guess the machine' game!
As John says, if it's s JVC then there will be lots of circuit protectors dotted around the machine, often not mentioned in the manual. They will have a number prefixed by N or F, usually 5, 10 or 15, which oddly are multiples of 400mA - e.g N25 is antisurge 1A. They will be either on long legs or in an oblong package with a dent in the top mounted close to the board. In both cases they look like transistors with two legs.
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Old 16th Dec 2019, 11:55 am   #5
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Default Re: PSU dead in VCR

In the end, finding a schematic or some knowledge of the machine would be the way to know where to measure exactly. You should give model and type number for that.
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Old 16th Dec 2019, 1:21 pm   #6
MusicWorks
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Default Re: PSU dead in VCR

Thanks everyone for your replies, I am back with all the information:

The VCR is a high-end S-VHS deck model JVC-S378U (1991). Very good guess indeed those who mentioned it looked “JVC-ish” It is a semi-pro deck, with a very nice transport NTSC only -it was marketed both in Japan and the US. This one is a US 120V model.

Finding the service manual was a pain, these are hard to work on -mechanically they are complex, disassembly is difficult, they have many sub boards...That is why I almost died yesterday after having this beauty up and running, as mentioned I did a blanket recap of the PSU, fit a new capstan motor and greased/oiled accordingly.

Took the PSU out this morning -cracking these open is a breeze (sarcasm off(). There are several of the ICP protectors you mention, that look like a two-legged transistor and marked as you say (N10, N20 and N35).

They are marked in the schematic as CP1 and CP3 and are highlighted in both the diagram and the actual board. There are therefore two of this ICP components in the main board (01 SW REG). I just tested both and CP3 is where the open circuit is.

The two points I accidentally bridged with my multimeter are TP1 and TP2 on the smaller board (02 REGULATOR), test points for both the +5VDC and +12VDC rails.

Interestingly enough, there are another two of these ICPs on the Power Trans board (03) in the schematic they appear as fuses F51 and F52 in front of both bridge rectifiers, they both show continuity. I have attached detailed images of the schematic, so you can see each one of the three boards. The only actual glass fuse in a fuse holder is F1 (1A/125V) in the main board 01 SW REG which I tested yesterday and is fine.

So, my guess is that replacing the fried ICP-N20 in position CP3 should solve it right? Given the other 3 ICPs show continuity on the PCB, single point of entry and exit so I didn’t bother to lift a leg and tested them soldered in. It seems odd however that there is not even power in the switched output receptacle (where the only relay is in the main board).

Would the ICP also protect this external outlet?

Best forum ever!

- MusicWorks
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Last edited by MusicWorks; 16th Dec 2019 at 1:37 pm. Reason: Correction
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Old 16th Dec 2019, 2:47 pm   #7
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Default Re: PSU dead in VCR

It's likely. You shouldn't have a problem finding one that works - if you can't get the exact replacement (antisurge, 800mA) then a Wickman fuse of similar spec will do which are easily available. I'm sure if you have a problem Ben on this forum who's also in Madrid can help you source one.
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Old 16th Dec 2019, 5:02 pm   #8
toshiba tony
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Default Re: PSU dead in VCR

Excellent, putting 12v on the 5v line sounds fatal, but if the CP failed immediately (as they should) you may be ok. Sounds a top machine, I always liked machines of that era. There was one range of their machines, admittedly just before that one, where the tape guides would just fall out, I don't know which deck you have but yours may suffer the same problem.
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Old 27th Dec 2019, 7:45 pm   #9
MusicWorks
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Default Re: PSU dead in VCR

Success!!!

After waiting for a week for the exact replacement to arrive from London, the VCR is working perfectly again. All I had to do is replace the open ICP (CP3) and this component did indeed protect all circuits as it should. So happy!!!


Manu thanks guys, kudos to you all

- MusicWorks
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