Radio Road Which tuner to get and getting the most from it. Thank God, for the radio!

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RE: opto-coupler problem

Posted by Marantzguy (P) on September 22, 2010 at 16:52:36

In Reply to: RE: opto-coupler problem posted by Balazs on September 22, 2010 at 11:26:00:

Hi, Rob and others:

I had this very elaborate response ready to post and just lost the whole darn thing!

Below is a resource you should carefully examine. It represents the most complete assembly of such information that I know of or have come across and it has fairly recently been made available to us for FREE on the web. THANKS TO WHOMEVER for DOING THAT!

:-)

If your opto-couplers fail, you will see a straight vertical line or a straight horizontal line on your display. A diagonal line in the stereo mode would tend to indicate either a weak signal being switched to mono or failure of the circuitry responsible for proper switching. There are bulletins about this on the site I mentioned.

In addition, there are a few little suggestions also included on this site which are very helpful to any 10-B owner. Testing and or swapping tubes may restore proper operation to the tuner. I once helped a local owner who called and told me that he could only receive signals in the upper portion of the FM spectrum. We tested tubes and discovered a weak 6DL4 in the front end and when it was replaced, this restored proper operation to his tuner.

Basically speaking, the opto-couplers contain either a single neon lamp and a pair of cadmium disulfide photo cells (CDS cells) or in the cae of the module controlling muting function, that module has inside of it only a single lamp and a single CDS cell.

You can remove them and slice them open with a jeweler's saw. Inside you will find a wafer of styrofoam with the aforementioned parts mounted through it. The whole affair is shielded from any stray light with a collar of black light-absorbant material.

I believe the aside from failure of the opto-couplers, the only other trouble involves what we call "spontaneous loss of detection". And, I jokingly say that only the guys in GhostBusters can help us all in that regard!

I have made my own replacements for the opto-couplers from parts found right off the shelf of RadioShack in the past. I do not know the exact specification for matching the CDS cells, however and have never actually seen it published.

Lastly, to my knowledge, only L&M Electronics in San Francisco, ever offered an upgrade modification for the failing optocoupler units. The owner, a fellow who goes by the name "Wally" (for Wolfgang) designed a small circuit board on the basis of some integrated chips which took the place of these funky old neon-lamp / CDS devices. In the early eighties, it would cost you $150 for that mod, and if he still offers to do this, you can only guess what it might cost you!

There are after-market home-brew replacements for the opto-couplers often made available via eBay. They are about $125 or so for three units, I believe.

I have no experience in using them nor do I have any opinion on them or the person offering them for sale.

But they are there if you need them!

Good Luck!

Richard Links
Berkeley, CA

• Service information on Marantz 10-B Tuner   (Open in New Window)

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