Marantz 2275 Multiplex problem

I have a Marantz 2275 with some issues. I got it off Ebay along with 4 other vintage receivers, but that's a whole other story.
The first thing I found when I went to replace the dial lamps was the plastic housing for the indicator lamps was MELTED! Not a good sign. Then , the FM indicator light stayed on no matter what input was selected. Then I noticed the Stereo indicator light was out so I checked the lamp. It was blown. Then I checked the audio, sound out of both channels but didn't sound like it was in stereo. Pressing the Mono buttons doesn't change the sound at all. I cleaned pots and switches and the problem with the FM indicator went away. I replaced the dial and meter lamps and the stereo indicator lamp. The stereo indicator still does not work and the sound is still always in mono.
Does this sound like a problem somewhere on the multiplex board, and what is usually the cause of failure in the MPX?

I may be able to work something out with the seller ( I have other bad units from him as well), but if the fix isn't too bad, I would rather keep it.

 

I have a similiar problem with my 2275. All I know is that the light bulbs that were soldered on to the clips, yup soldered...totally burnt and melted the housing caused something downstream to fail.

Hopefully I can pick up some hinters from this thread too. If not I'll have to take it to a tech and I'll let you know what happens.

Good luck

 

My second Marantz 2500 wouldn't go into FM stereo. It was fine from a CD source. Luckily, I had just scored a crusty parts machine. The fix involved changing a chip in the tuner front end. Don't know the details 'cause my tech did it.

 

This site gives a little info on the cause and a part number and possible source for the decoder IC.

http://www.classic-audio.com/marantz/mtips.html

- Dave

 

I was thinking it may be the IC, but wasn't sure. Guess it would be a good place to start.

 

Thanks for the info. That was very helpful, as that may very well be the problem. It says using the wrong stereo indicator lamp could blow the IC, and it appears the lamp was replaced.
One of my suppliers at work (I buy IC's for a living) has them in stock, so that should be easy to replace.
Next question though, what is the proper lamp for the stereo indicator?
I don't want to blow the good IC's as well.

 

I doubt if using the wrong lamp would completely blow the IC, just the lamp driver, it should still demodulate stereo. It is possible (in fact likely) it's just an adjustment, and/or the tuner needs alignment. There is an adjustment pot for the multiplex PLL, get the service manual and locate the pot. You can just adjust it so the stereo light comes on, or if the light doesn't work, listen for it to receive in stereo. Adjust for the mid point of where stereo comes in.
For the lamp you can use an LED in series with a 1K resistor. That will limit the current to about 10mA.

 

Even is someone did this?

http://audiokarma.org/forums/attachment.php?attachmentid=28658&d=1161669732

http://audiokarma.org/forums/attachment.php?attachmentid=28659&d=1161669732

 

Those lamps are so wrong for that Marantz its not funny.

Marantz took fuse lamps originally at 200mV but it is hard to find as there are tons of 250mV on the market. You will melt the bezel again with 250mv, I did on mine.

I replaced them all with the LEDS on ebay,they are terrific NO HEAT!

But those lamp boards look like a mess.

The lamps are driven by a seperate leg off the transformer. Unless something melted down into the MPX section below I can't see how they would affect the FM.
You'll know more once you try it with other sources to see how it sounds then.

Good luck with it.

 

The Stereo lamp is not a 8V 200ma fuse lamp!

It's a bi pin lamp, 12v 40 ma or 2 bi pin lamps 6.3v 40 ma


Tony

 

Shouldn't matter. Inside the IC is one circuit that detects the stereo 38KHz and another that drives the lamp. The driver would blow and the lamp would not light, but the stereo should still work. Of course, if you want the stereo indicator to work you have to replace the IC which amounts to the same thing...

 

Tony, I was referring to the scale illumination board he had pictured there. Go back and look.

Jon

 

Always use the correct lamps in Marantz units, go cheap and you deal with headaches like you're encountering, Dave. :nono:

 

What IS the correct lamp for the Stereo indicator?
I keep reading it is a lower MA than the rest of the indicator lamps and keep reading people are blowing the Hitachi IC when they use the 40MA.

 

The Marantz 22xx series either use a pair of 6.3v/40ma bi-pins in series, or a 12v/40ma bi-pin, or an 8v/60ma with red & white wires, we need someone with a stock unit to check, or a service manual, my lamps have the OE part# on their boxes so they should match the service manual parts list. 40ma lamps won't ruin the IC, it's when people start using much higher ma values that cause problems, Dave.:yes:

 

I checked the service manual for the 2275.

bi-pins - 8V, 0.04A
fuse bulbs - 8V, 0.2A

 

So the information on the Classic-Audio website is not correct?
This is what it says:

WARNING! The FM stereo light requires a lower current lamp than the other indicators in circuits using the HC1000401 PLL IC. Using the same bi-pin lamp overloads, and can blow out, the stereo decoder IC. That is why I had to replace the HA-1156 mentioned above! I do not have a source or details on the current requirements for the bi-pin stereo indicator lamps. If it is the stereo indicator you need, be sure to tell the Marantz representative that!

Here is the link to the site: http://www.classic-audio.com/marantz/mtips.html

 

Not disagreeing with anyone here, this is just what I figured - no amperage listed in my manual, so to play it safe I went with 8v,20 milliamp. Mine is the single wired in lamp, not the bi-pin pair. (2238B)

As far as the accuracy of the Classic Audio site, I dunno for sure, I don't have a real lot of practical experience, they warned, I listened.

- Dave