JVC 9500 no normal audio, but Hi-Fi audio ok?

[MarkyM]

Hi,
I am wondering if anyone can point me in the right direction on this.

My trusty JVS HR-S9500U has stopped passing the mono "normal" audio on older tapes. Hi-Fi audio on "newer" tapes is fine.

It will "pop-in" occasionally and then quit again. It seems to work the longest from cold, when the unit has been unplugged for a while or overnight.

When the audio quits, it also disappears from the front panel audio meters.

Video is always OK.

Looking at the schematic, the playback head pretty much goes right into the big 100-pin LSI chip after passing through a 10uf electrolytic cap. I have changed that cap with no improvement.

Any ideas of what to check/replace next?

By the way, this thing is really made with servicing in mind. The whole transport lifts out after removing 4 screws, 2 nylon standoffs and 3 ribbon cables. The front panel has no screws at all and the main board is super-easy too! Very nice to work on.

--Mark--

[hodgey]

The "normal" audio heads don't sit on the head drum, as linear audio is simply a raw audio waveform similar to cassette and reel-to-reel tapes.

vcrxprt.gif
(Image from the vcr faq)

So I would start looking there and if the audio signal makes it's way to the test points.. Maybe it's just the ribbon cable that's a bit oxidised.

And yeah, the jvcs are generally nice to work on, except the fact that they use a rare special service remote for electrical adjustments.

[MarkyM]

Thanks,

I don't think it's the head itself or that ribbon cable because when it is working and I touch the cable, there's a buzz generated in the audio as you would expect given that ita an unbalanced high-impedance circuit. When its not working, there is no buzz. I have removed and inspected / re-inserted that cable and it looks good.

I will trace it out though.

[dpalomaki]

Quote:

I will trace it out though.

Good idea. Since you have the schematic try trace the linear audio through the circuit to see where it disappears. Might be an intermittent solder joint on the board that opens when the machine heats up. Does the audio last longer if the case is open?

[MarkyM]

Quote:

Originally Posted by dpalomaki

Good idea. Since you have the schematic try trace the linear audio through the circuit to see where it disappears. Might be an intermittent solder joint on the board that opens when the machine heats up. Does the audio last longer if the case is open?

Will do.

Not really. Seems about the same.

[qcalv]

Hello,
I have a similar problem on the JVC HR S9600MS. I get no sound. I looked as well at the A/C head and the ribbon cable and did not see any issue. It's reading newer tape with HIFI but older private tapes with mono in NORMAL mode not. So I was wandering if you solved your issue? And if yes, how?