CD-4 Disc Demodulator JVC 4DD-5 . Please help.

Going back on topic here ---

I want to mess with the one JVC I have that has full sound and two equal channels, but no decoding on the right side. I can pull parts from 2 others I have. Can someone suggest which parts I might start attempting to replace? I have no equipment other than a soldering iron and very minimal soldering skills (namely, none). Any suggestions appreciated. I have enough of a brain to read a schematic, so part numbers to try swapping would be a helpful place to start.

To my thinking it's 50/50 whether one or a few bad capacitors would cause that, or outright failure of an IC or transistor. The cost of all the caps in that (from Mouser or DigiKey) would be less than the equivalent time to pull each used (questionable) one off another unit. That's where I would start, just my opinion and a guess.

I think I'm in over my head with this. I just looked at the schematic, and I have no clue which capacitors to even attempt to replace. May have to pay for repairs, buy one that's known to work (or other model), or just live with the crummy-ish sound from my one JVC that does function.

Glad you came to your senses without prodding.
You could do as I have done and set up a search in ebay for
CD-4 Disc Demodulator
Over the past 2 years I have acquired ...
Two Technics 4-channel receiver quadraphonic model SA-8000X
(I only use the CD-4 decoder in those. It is SC Cartridge compatible.)
A Panasonic SE-405, also SC Cartridge compatible ($41 and working well)
(One of my Carts is an EPC-450C-II SC or strain gauge)
A Marantz CD-400 ($185 almost identical to the JVC 4DD5)
And 1 of those "new in box" JVCs that worked (out of 4)
Why so many?
I have 2 quad systems in different rooms and it's a good idea to have backup
and working spare units.

And the 45 rpm discs that come with those JVCs?
I found that all of them give faulty reading in right channel separation.
You would also do well to look for other makers of discs to set up the demod.
My favorite is a very rare Hitachi demo disc only released in japan.

Very important, ask the seller of the CD-4 unit if it actually demods properly.
Some are misleading as they will say "works great" but all they have tested
is whether a regular stereo lp plays through the unit.

Thanks for the info again. What's your preference sound wise? Which one of the demods sounds the best?

I can only safely state that none of them distort on any of my CD-4s.
The perceived sound quality will depend mainly on the cartridge and CD-4 disc.

Just for grins, I opened up the JVC that's not decoding right. The one that doesn't' decode at all on the right and minimal decoding on the left. I pulled it all apart and there was a ton of oxidation on the bottom of the circuit board. I cleaned it thoroughly, but it didn't make a difference. On both left and right, if the adjustment knobs are turned all the way up (clockwise), all sound vanishes from both channels. The right one is more problematic and doesn't decode at all. And even with adjustment, the left one only decodes minimally.

I'm not sure if the parts directly connected to that control are the demodulators. If they are, is it worth trying a transplant or does it still sound like a power cap issue? Swapping out that entire switch is easy, but it those are just attenuators or something, it's not going to fix the issue. I Just checked the service manual and they're def. just volume knobs. Could those be the issue? I'm thinking "no."

Don't throw the demodulators away. If you do that, they are gone forever. Put them up on Ebay as non working units, or if nothing else, if you don't want them, just send them to me. I don't have time to do it now, but eventually I might can get them working. If you want them back, I would just charge you for the repairs. If not, I would just put them up on Ebay.

I'll hold onto them. Maybe I'll send you the one almost-working one some time down the road. By the time I pay shipping back and forth, I may find one for the same price on ebay that's known to be fully functional. I'd like to try the Pioneer that has the switches all on the front.

of course, i tend to get itchy and I may be shipping one of the JVCs your way sooner than I think. Thanks for the offer, too. If you PM me your address I can keep it on file.

Rich

My main concern is that these devices be preserved. Working or not. One can't fix them if they don't exist. Just contact me if you decide to do it, I'll send you the info then.

surroundme33 said:

Thanks Quadjoe for responding. I have posted a DTS version in a previous post (although this was recorded with the Grado Cartridge - the AT12Sa is similar. Here is the link again http://sendshack.com/download/4htqi64

And regarding bleed - it bleeds very loudly front to back - even if i place the adjustment in the hardly audible range. I am going to say (although i can't really confirm) that it sounds like an SQ with a very early decoder with poor separation. Please, listen to my DTS sample and let me know..

Thanks again..

Click to expand...

Surroundme33, I have a copy of the JVC CD-4 setup record I can lend you if you're interested. PM me and we can get together on it. It's a better setup for that demodulator than the Fisher record, which I found sometimes doesn't work as well.

Would someone let me borrow their JVC 4DD-5 demodulator setuip disk? I will pay for shipping both ways. I'm serious, not planning on ripping anyone off... I am in NY... Thanks

It's the same 7-inch test disc that can be found all over (Hitachi, Argo, off-label, etc) with the 4 test bands on one side and The Godfather Theme on the other.

But these do just as well and are also all mastered at the JVC Cutting Center in West Hollywood. Plenty on eBay for less than the round trip shipping:
http://www.ebay.com/itm/HARMAN-KARD...rial-LP-RCA-/311235799863?hash=item4877196b37

http://www.ebay.com/itm/LISTEN-FISH...876?pt=LH_DefaultDomain_0&hash=item2c9d955e0c

http://www.ebay.com/itm/The-Fisher-...-Light-Quad-/381341515652?hash=item58c9b9bf84

Thanks for the info - I thought I needed a JVC specific LP - I bought one and will have it in a week! I grabbed the Harman Kardon one since it was a buy now... appreciate the help!

Also in order to avoid destroying your CD-4 vinyl, remember to get a new genuine Shibata stylus from Japan or Germany (no knockoffs e.g. nude square shank hyper elliptic, tetrahedral, quadrahedral, micro line/line contact etc.) for whatever CD-4 cartridge you happen to be using - or else send off the stylus you have to a re-tipper to get the right alignment. knockoffs are NOTORIOUS for being out of kilter - not only slicing and dicing your delicate CD-4 vinyl - but just about every other record you own as well.

In addition to that - cartridge needs to be relatively flat to at least 60K) or certainly 50K as many ``CD-4 compatible'' cartridges drop off sharply as low as 35K or 40K - which will account for a good amount of a sandpapery sound upon demodulation of even a mint-condition and well-mastered CD-4 LP.

One you should get if you don't have it is the Elvis: Aloha from Hawaii but ONLY GET THE BLACK LABEL RCA SPECIAL PRODUCTS EDITION. Don't get orange label or tan label or yellow label or any other label but black.

The SP editions were re-mastered onto CD-4 in 1979 just before JVC CC in WH closed down. It was also pressed onto 160 gram vinyl instead of the normal 90 gram vinyl of all the normal pressings of the period (70 grams is what a normal 7-inch 45 uses) - and has the mini groove guard like on a RCA Shaded Dog that doesn't gradually slope down halfway into the first number.

Meaning whoever has a copy that has no pictures of the label - you'll have to write them and ask if its a black label RCA SP.