Panasonic SV-3700 Repair

I have this used Panasonic SV-3700 digital audio tape unit, which I've had for some time now. This was a unit that I really liked owning but the problem was that I hadn't used it in probably over a year.

The service manual is available from here: http://elektrotanya.com/panasonic_sv-3700_sm.pdf/download.html

I recently needed a source of digital audio so when I went to use it, the old adage became real - "If you don't use it, you lose it!". I could eject and insert a new tape cassette but attempting to play or record only caused the unit to stop and refuse to respond to the play/record controls. The only way I could retry was to eject and insert a tape again. And of course, I tried several other tapes with the same result.

After some sputtering and muttering, I decided to clear the workbench and see if a fix could be had. Figure 1 shows the unit opened up, with the transport unscrewed and placed sideways over a folded piece of paper to avoid short circuits. This afforded greater visibility for troubleshooting. The transport is seen in the center behind the front panel.

Figure 1. Opened Panasonic SV-3700, with transport moved for better viewing and servicing.

I was of the opinion that the belts were probably ok. After all, the transport seemed to load, unload, and rewind ok. The problem only occurred when a play or record function was selected.

With the transport repositioned so that I could better view the action of the tape as it wrapped around the heads, I noticed that the head cylinder was never spinning. Could it really be this simple?

Figure 2.  View of the head cylinder from the end of the transport.

Reaching in carefully with the unit off, I touched the cylinder on the corner between side and top, to avoid putting any oil on the head. I noticed some resistance at first as I tried to make it turn. Then it seemed to break free but still had a noticeable amount of resistance. It was time for a power on test!

I powered the unit on and loaded a tape. I set it to record and then I saw a reluctant but spinning cylinder! Shortly after, the spinning overcame all resistance and seemed to continue with a proper smooth spinning action.

Rather than buttoning up the unit right away, I chose to allow it to continue recording for an hour or so (the length of the tape). I wanted to make sure that any built-in lubricants had a chance to reach places where they were meant to be. I also wanted any current "stickiness" to be eliminated by active wear.

And then there was more..

After it successfully recorded for an hour or so, I stopped the unit and requested a full rewind. The unit surprised me by doing a slow rewind and then stopping after about 10 seconds. And then it would retry about three more times. After the third stop, it simply gave up.

This didn't look hopeful but I unloaded the tape. Then I manually turned the spindle drives back and forth with my fingers to overcome some other potential "stickage". 

I reloaded the tape but was not at first successful. Then all of a sudden during a slow rewind attempt, the spindle sped up to full speed and has worked ever since. I naturally spun the tape back and forth a few more times to make sure.

Epilogue

I have since put the unit back together and it continues to work ok (though probably needs a head cleaning). 

So if you have mechanical devices, particularly tape devices, take them for a spin today. If you don't use them, you may lose them.

Thanks for reading!