Panasonic SV-3700 Post Roller Adjustment

I recently aquired a Panasonic SV DAT machine (SV-3700) and found that while it would appear to record (receive digital signal to meter, monitor audio through), and then go into record mode, as well as playback mode when I hit play, it would not playback, nor actually record audio. If you get the service manual (download here), you can find out how to check the error codes the machine will send when it fails. Mine would ‘play’, though not reproducing audio, for about a minute, then throw it’s error code and lock the transport, with all buttons un-responsive until you either eject the tape, or cycle power.

Running through the codes, it was a code Exx04, meaning Cylinder Unlock. So after a thourough clearning, reconnecting all the connectors inside (in case they had been damaged during transit) I decided to try a ‘Linearity Adjustment’ and see if any difference was made.

‘Linearity Adjustment’ is done via rotating the post rollers, which varies the height of the tape, and accordingly, varies the path at which the tape crosses the cylinder head, and accordingly, the playback and record heads.

To get to the adjustment stage, you need to remove the loading mechanism, which is failry easy and explained in the service manual, it’s four screws.

I made a little adjustment to the post roller that sets the height to the cylinder head, about a 1/4 turn, and then a bunch more turns (the manual says to not make more than a 1/4 turn correction, this thing was WAY OFF) and all of a sudden the tape began playing audio, though it was extremely distorted, both in gain, and in low-bit rate. A further turn of the post roller yielded the tape to play perfect sound. I then adjusted the post roller that sits after the cylinder head.

The issue with adjusting post rollers that can make it problematic, is if your machine is set to record it’s info to the tape, somewhat askew, then the next machine that plays it, may not be able to read it, unless you adjust it’s head to be in the same position. So you are at once trying to set the machine to playback and record to tape with the least amount of errors, but simulatenously, it may be at the price of compatability with other machines.

So, at this point, I put the machine into ‘error detection’ mode, and began adjusting until the errors evened out to a lower number, varying between 48 and 170, before finally settling down around 64.

And that was that. This deck was used, and was sold by a University to someone else, who then sold it to me. So it’s quite possible that the University chucked it, simply because it needed a post roller adjustment.

After the adjustment, the error code stopped being sent, and the Cylinder Unlock condition ceased.

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Llamatism is a collection of things, a cabinet of curiosities, and reports from explorations on things, by Gary Llama.

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