View Full Version : Yamaha CR-820: no stereo in FM mode?


Benz
01-17-2009, 08:52 AM
I did some searches, but couldn't find anything on AK about this issue:

When in FM mode, the stereo light never comes on and output is audibly mono only. Setting the unit to stereo, mono, DTS on or off makes no difference...

I looked a bit when I replaced the lamps recently (thank you dgwojo!!), but wasn't sure where to start. Any ideas on what could be causing this?

Thanks in advance for suggestions!

Edit: found this thread [http://www.audiokarma.org/forums/showthread.php?t=202752&highlight=yamaha+stereo+problem], but not sure if this would help me...

wajobu
01-17-2009, 08:57 AM
AK member Merrylander will know the exact adjustment/location, but it's likely the "VCO" variable resistor on the FM circuit board (usually labeled with the letters "VCO"). Typically (like with my CR-620) if one tunes in a known FM-Stereo station and then with a non-metallic screwdriver slowly turn the VCO variable resistor slightly, eventually the stereo signal will pop-in--BINGO! Before you do this (if you find it), just make a note of where it was set originally before you adjust it (in case it doesn't work).

But, it has always worked for me.

Benz
01-17-2009, 09:00 AM
AK member Merrylander will know the exact adjustment/location, but it's likely the "VCO" variable resistor on the FM circuit board (usually labeled with the letters "VCO"). Typically (like with my CR-620) if one tunes in a known FM-Stereo station and then with a non-metallic screwdriver slowly turn the VCO variable resistor slightly, eventually the stereo signal will pop-in--BINGO! Before you do this (if you find it), just make a note of where it was set originally before you adjust it (in case it doesn't work).

But, it has always worked for me.

Thanks Wajobu, I'll try that - sounds like a relatively easy fix.

... so you would do this while the receiver is on? Any risks doing that?

orionkc
01-17-2009, 09:06 AM
Nor risk if you use a non metallic screwdriver. The only way you can adjust it is with the unit on. Good Luck!

wajobu
01-17-2009, 09:07 AM
Yes and yes.

Since I have a wooden work bench (not metal) I usually prop the receiver chassis up on a couple of wood rails and make sure that it's touching nothing else around it. I take off my wedding ring (and don't wear a watch anyway) and generally stand on an isolated rubber mat on the floor. I get all set up with a temporary antenna, stick one hand in my pocket and use the other hand to make the adjustment and watch for the stereo signal. I do my best NOT to touch anything "under the hood" while I perform this (or any other) adjustment. I'm certainly NOT an expert, but have not had any shocking experiences...yet**. Unplug everything before starting and then when reassembling.

I use a "temporary" set of speakers at my workbench to test equipment.

Many other far more experienced than I will certainly have other advice. I NEVER do any work on my tube equipment...I send THOSE to the experts due to the high voltages. But if you have any doubts about doing this, by all means, send it to any one of AK's or your local electronics techs.

**-although I did once fry some amp outputs by accidentally touching a diode with a metal tip on a cleaning brush...lesson learned...only non-metallic cleaning brushes!! :nerd:

Benz
01-17-2009, 09:35 AM
Thanks so much for the tips.

I will attempt the procedure this weekend and report back with results!

merrylander
01-17-2009, 10:48 AM
On the tuner board at left front is a small square transformer/coil. It has a variable resistor behind it and another one to its right. The one to the right is the one to adjust, it controls the 19kHz free running oscillator, in fact the test point is a little over an inch toward the back of the chassis. My Triplett DMM reads frequency so I usually connect it there, but the method using a known stereo broadcast is just as effective.

Benz
01-24-2009, 01:02 PM
Finally finding the time to work on this...

I opened her up, and taking a closer look, I'm not 100% sure which variable resistor you are referring to Merrylander... is it #1 or #2?

http://i297.photobucket.com/albums/mm208/benath/CIMG6391.jpg

Thanks in advance!

wajobu
01-24-2009, 01:11 PM
Merrylander will tell you for sure, but what you are looking for is something that looks like those two flat silver discs lying on their sides with the slots in the middle, right next to the tuning core metal fins. On my CR-620 (and on the 220 and the 420) it's labeled "VCO". In the photo at the upper left one says "FM Meter"--the one to the immediate right I can't read.

In this photo (of a CR-440 or 640--later model), look at the left, below the blue ribbon connector, there is a variable resistor labeled "VCO" (just above the word "Do" at the white lettered written question). That's what you want. If only I had a circuit board layout handy, I could help you locate it--DRAT!

http://www.audiokarma.org/forums/attachment.php?attachmentid=83910&d=1206235151

Benz
01-24-2009, 01:26 PM
... would it be one of these two: FM Meter or VR101 ?

http://i297.photobucket.com/albums/mm208/benath/CIMG6391b.jpg

merrylander
01-24-2009, 04:01 PM
This one, VR201.

Dark Knight
01-24-2009, 04:21 PM
This was a great learning experience! Thanks. Hope the problem is solved.

DK

Benz
01-24-2009, 04:41 PM
Success!! :music:

I now have a strong stereo signal. Thank you so much Merrylander and Wajobu for your help and patience. At first I wasn't looking in the appropriate area as I hadn't realized the tuner board was the whole right half! :scratch2:

LOL pretty obvious I am a beginner at this - even more credit to you guys for managing to explain to me what needed to be done.

Thanks again guys!

Edit: just became a subscriber too! :banana: