JVC VCR...audio issue
 

Hello all,

A few months ago I introduced myself and showed a few pictures of a JVC VCR that I picked up at a thrift store. A little while later, I managed to come across a decent quality A/V receiver on the cheap that I could hook it up to. Thought I'd give the unit a proper tape to play so I threw in 'A Show of Hands' by Rush.

I will say right now that the video itself seems to work just fine. The problem that I have with audio seems to coincide with the 'audio monitor' feature that this unit has. There are two settings, 'normal' and 'hi-fi,' and when it's in 'normal' the sound comes through just fine. When it tries to switch itself to 'hi-fi,' however, the audio cuts out. Then I guess it senses there's an issue because it switches back to 'normal' and I get my sound again.

I really like this machine and I'd very much like to enjoy it. Anybody ever encounter an issue like this?

http://oi43.tinypic.com/2f03rbl.jpg

If you have not done this already try a cleaning tape in case the HIFI audio head might be dirty.

Another possibility is that the HIFI decoding circuits need repair (it's old enough for cap failure to be happening).

JVC embedded the hi-fi audio (20 Hz to 20 kHz) in to the video track in a scheme called Audio Frequency Modulation (AFM). It was located in a small RF signal gap in the video track in between the luminance and color carrier video signals.

As the audio was in the video track, JVC refined the audio switch to insure continous audio. The video switch would make a sloppy video head switch at the end of each rotation of the head which you can see at the bottom of the screen in the last few lines of video on most VHS tapes as staggered scan lines.

This deck will only play back hi-fi if it was recorded that way. If you have ordinary longitudinal, edge-recorded audio tracks (stereo or mono), the hi-fi will hear nothing and not work. This deck will play both via the audio switch.

Your Christmas 1984 tapes will be old school edge audio. If you can find movie studio tapes from that time and after, they will probably have hi-fi. I don't remember if any home camcorders recorded in hi-fi.

Does the deck have any kind of Time Base Correction? It would probably be a switch-on-switch-off function. They did this later in their high-end VHS decks along with digital correction and those playbacks look great. TBC was the only thing you would get in the 80's. Digital was a few years away.

That sure is a BEAUTIFUL deck. Sure hope you find out the issue. Wish I could help you.

Well, now I feel like a bit of a dummy. :stupid:

Turns out the reason for the sporadic audio had everything to do with the tracking adjustment. I poked around with some of the stuff on the front panel and apparently you can use the level indicator to adjust hi-fi tracking for your tapes. A very helpful feature! :thmbsp:

I also found a service manual, but I'll end up needing a neck brace after I read through it because the whole .pdf is sideways. Once I get a new toner cartridge for my printer I'll see about printing all 149 pages.

Now all I have to do is replace some rubber and I think it'll be ready to keep on playing.

If you open it in Adobe Reader you can do View, Rotate View...

Glad to hear it was just a tracking issue, that is a seriously nice deck.

Used to see those 8000s come in the shop with burned up switching power supplies. That was 15-20 years ago! The plastic insulator sheet between the shield case and circuit board would be burnt black in spots. Would highly suggest inspecting that and replacing capacitors as needed.

Rotating the pages helped immensely. Thanks for the heads-up. :thmbsp:

Also Dave A, thanks for those bits of information. I honestly had to do a little research on the workings of Time Base Correction but that helped me get a better idea how some of this video gear works. Very helpful. :D

They certainly do seem to get hot don't they? After maybe ten minutes of use the power supply felt pretty toasty. Seems to be a common theme with JVC gear. All of the Dynamic Super A receivers I've had run surprisingly hot, and apparently the motor housing on my turntable was sufficient enough for a spider to incubate eggs.

Either way, I'll be sure to do that. I'd imagine it probably needs some manner of electrical work anyway.