Marantz 2220 no stereo in FM

[ringading]

I am restoring a 2220 I picked up for $50 off CL. Cosmetically it is in mint condition. It had horrible static in both channels and a very low right channel but recapping the P700 board took care of that. Sounds clear and clean now!

But of course as happens on these old units, something else cropped up.

I now noticed that it won't do stereo in FM - no stereo light. I replaced them both with the proper lamps (thanks dgwojo) and they work great in aux or phono.

I read a thread (http://www.audiokarma.org/forums/showthread.php?t=157920) about adjusting the trim pot on the MPX board for a 2220B that solved the problem for a couple of folks. However the board on the 2220 is different. From comparing the two SM it seems that it is the R304 trim pot on the 2220B and the equivalent on the 2220 is the L303. Does that sound right? Getting a little :thmbsp: or :thumbsdn: from the great folks here would go a long way.

Anyone else run into this problem? I know a full alignment might be in the cards or the MPX chip might be the kaput but I don't know if that is replaceable or not.

FYI - I am no repair tech with no formal training, just learning my way through by reading through all of the great posts here.

 

[rBuckner]

I would say you could try messing with R329 but MARK IT FIRST with a felt pen on the pot top referenced to something fixed in place so you can go back to that spot. If that don't get it put the pot back and measure the transistors' dc voltages against the schematic. Good luck!

 

[catrafter]

The 2220 has no MPX 'chip', it is a discrete design similar to the 2230.
There is a pretty good description of it's operation in the 2220 service manual, pasted here:

The 2220B, however, does use a MPX decoder based on an HA1156 'chip'. If the Stereo lamp works in aux, phono and tape, and goes off when you select Mono in those functions, then there are other things to look for other than the mono switch.
The path for the stereo lamp in FM Stereo operation is pin 6 of H301, through R311 to pin J305 then to S001-1 pin 6 then to S001-1 Pin 5 (because it in the 'FM' position), then over to JH11, through the Mono switch which is not pressed, out JH10 to one side of the 'stereo lamp. The other side is connected to plus 7VDC, the source.

If you don't have a frequency counter, set the selector to FM and tune in a strong station, that is, one that will send the signal meter up at least half way. Use an antenna of some sort if you need too, I can usually get away with a foot or two of wire. If the base of H303 is less than 0.6VDC, and the collector or Pin 8 of H301 is above 2VDC, then check H301, pin 14. If it is above 3VDC, then mark where R304 is now so you can set it back if things don't work out. Now try moving R304 a bit each way and see if the stereo lamp comes on.

Expanding on the operation a bit, the levels in parentheses () are what you should see on the P300 board for FM stereo operation. Look for less than 0.6Vdc on the base of H303, it monitors signal quality and shorts pin 8 of H301 to ground if it's too low, forcing H301 into mono operation. The VCO test point at R312 (TPB on the schematic) should be 19kHz. If there is nothing there, H302 could be on or shorted emitter to collector killing the VCO, It's base is driven positive when the selector is in AM to prevent interference.

Tom

 

[wynnyrdg]

Did you ever fix?

 

[johnhoef]

An old thread, but thought I would give this a try. In my case, I find two of the four coils in the multiplex board are open. L301 through L304. I have successfully repaired tuning coils in the past, but these are too far gone! Corroded wire, and the plastic internals crumbling!! They need to be replaced. So, my question - where can I get replacements? They seem simple enough. According to the service manual, 56mh, and 43mh.

 

[rBuckner]

Your best shot is finding a used whole board on eBay and robbing that.