Panasonic NV-GS50 cylinder lock issue


First of all, I got an issue with the LCD locking mechanism which got broken. So I had to disassemble the LCD housing in order to reach the broken plastic holder which I successfully repaired thanks to some glue. However, after reassembly, the LCD was missing backlight. After some investigation and help from a repair forum, I got the issue fixed by replacing a fuse on the mainboard which got blown most likely because I forgot to remove the battery while servicing the LCD: a permanent voltage called M NOREG is supplied to the LCD and the flat cable has the M NOREG next to GND which made a short while reinserting the flat cable.
Again I successfully serviced this second issue but after reassembly I was getting a new issue, this time about the tape mechanism. When the camcorder is OFF the cassette refuses to load, and the only way to have it put in place is to turn on the camcorder but when the tape is brought down by the loading mechanism, the message “To SERVICE” is shown on the LCD. I triggered the error code by following the procedure as described within the service manual, and it shows “F05 cylinder lock”.
I put some pen mark on the cylinder which confirms the cylinder is not rotating at all. So I started some deep investigation with the help of a scope. When a tape is inserted I see the /Cylinder ON pin on the motor’s driving IC going low for 2 seconds then high again. I also made measurements for the voltages across each of the 3 frum's motor coils (= between the coil terminal and the coil’s common pin) and I read a “perfect 0” which means the issue is not within the tape mechanism but on the mainboard. In my opinion I have to find out why the motor’s IC is not triggering voltages across the drum’s coils.
However, I lack documentation about the motor’s IC which is a 64 pins proprietary IC. I also took measurements for several signals, but the service manual put only DC values onto the schematics. There is a Triangular several hundred KHz 500mV waveform going from the power supply IC, a 400KHz DRIVE CLK signal… All that seems OK…

More strange are the YVM and YSW signals values. Not sure about them but according to me, the YSW may be a square waveform signal which sets the YVM voltage by varying the pulse width so that YVM compensate for speed (FG) and phase (PG) variations (it’s my interpretation from what I’ve read from som documentation). However, as measured by myself, YSW is a DC voltage for about 7,6V even when the /cylinder ON signal goes low and YVM is around 7,9V. However, according to the schematics, YVM is 3,3V.

Maybe YVM is considered out of range which disables coil’s voltages (YM3, YM2, YM1)…

Do you know what are the key signals I may have to check on the motor's driving IC? As the tape loading/unloading mechanism is working, the motor's driving IC may be OK and the issue is to be investigated elsewhere. Capstan is rotating but a strange noise is coming from the mechanism. Maybe it is running a degraded mode to prevent tape damage as the cylinder is not rotating??

Thanks in advance.


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From 1995 to about 2000

I did design work on CCTV systems and they had service manuals for the camcorders used. I have no access to those but that is what you need now.

Or you scour Ebay for parts and boards to swap what you think is dead. Also these seem to run 100 (way too much for that old hardware but if you are trying to get your video out, worth it.)

That said, no one I know uses these to create new videos. Only for playback and digitizing. Yes, once in a while you find folk that won't give it up. It's only getting worse.

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NV-GS50 cylinder lock

As you suggest, replacing the mainboard may be the solution. However, knowing the cause of the issue may in some cases avoid replacing the board (ex: broken soldering joint). I have a couple of service manuals for this family of camcorders but the cylinder servo loop is poorly documented and I don't know what level (waveforms) I have to seek for in order to track the issue.

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Where we got our service manuals.

Was from the maker. At the time it was Canon and since the company consumed tens of thousands of these we had a contact in the company for when the manual didn't suffice.

Board level repair was done to a point and then it was swapped as you have to avoid over investing hours on your repair bench. Some folk don't get this is a business and not some one working at home for free. So not every board was repaired. I think over half were.

You are also battling age. I think these are from 2003 or 16 years old. Those that worked at the circuit board level are most likely gone and with them all docs.

As to broken solder joint the best tool I had for that back them was a good 100x power microscope. I would also reflow a chip or part if it was suspect.

We would reflow the entire board in the last ditch chance of repair.

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Servo IC datasheet

Thank for your answer. I agree most of the points and yes, the camcorder is from 2003. I understand it will be difficult finding additional documentation than that I already have but the good point is that the servo IC signals seem quite common as several other IC use the same namings:

Those are from Toshiba but the application circuit within the datasheets use the same PNP based transistor circuit for YVM management as for the NV-GS50. However, I still don't know what waveform I should have for the YSW signal. Also the datasheet lack information as they are mostly brief pinout description and test procedure.

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The techs on the bench

Over time would collect waveforms of good and bad. This was the usual repair shop for CCTV gear by a good size company. So we would have good and bad units to compare.

I think I've shared all I can and wish you luck.

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