Sansui 3000A FM stereo

I have this problem that just started the other day while playing Christmas music from the local classical FM station.I noticed the sound changed and the stereo light was out and gone to green (mono).I played with the tuner and it would come and go and almost sounded like it would click in and sound fine .I moved the antenna around but it had little effect.This is new to this unit and I have had it for 40 years.I repaired the power amp and driver (new caps and transistors) in the past year and I did the output mod with the help of you fine and helpful people.Any thoughts to lead me in the right direction.Thanks in advance Dan

The tuner could need aligned, or just cleaned.

1) did you do the amp stability mod? If not, the service bulletin is available here if you search.

2) I had a similar problem with my 3000A - a few transistors and a diode or two in one channel of the MPX board let go. Do you get sound from both speakers if you set the mono/stereo switch to mono, but only from one speaker with the FM selector set to mono but the mono/stereo switch on stereo? If so, the transistors are available from LittlediodeUSA on eBay. Not cheap, but not terrible either.

Yes,I did the mod for the output stability.I will try to see what it does in the settings you mentioned.It may turn out to be what you found with your unit,I will check them out and let you know.Thanks for the help.

I know this is an old post but I was hoping someone can lead me in the right direction. My 3000a will pick up an FM station clear in the mono mode but it is lower and has more noise in the auto or stereo mode. I beleive it is a problem on the mpx board and have checked all the transistors and they check good but I know they can still be the problem. I replaced all the elec. caps and the diodes test good but still could be the problem. I don't want to shotgun parts at this and any help would be great.

Keep in mine stereo mode needs more signal than mono.

danqth said:

I know this is an old post but I was hoping someone can lead me in the right direction. My 3000a will pick up an FM station clear in the mono mode but it is lower and has more noise in the auto or stereo mode. I beleive it is a problem on the mpx board and have checked all the transistors and they check good but I know they can still be the problem. I replaced all the elec. caps and the diodes test good but still could be the problem. I don't want to shotgun parts at this and any help would be great.

Click to expand...

It is possible that your source of FM signal (the antenna) might be a problem, if you lose some signal strength, the stereo operation will be the first to show it.

Anything that weakens the signal will be first heard on stereo and the tuner itself may to blame, the first thing I would look at is the tuning "gang" (the plates that rotate when you move the tuning knob) and try a SMALL squirt of DeOxit where the brass contacts meet the rotating shaft, DON"T spray any of the adjustment screws mounted on top of the tuner frame!

These contacts ground the tuner plates and any poor contact can cause you to lose signal.

Mark T.

Mark,I did not think of that I will give it a try and let you know. The signal is good, so I am hoping it is something I can repair.

I'd have to look up the part numbers again, but I think the MPX board on the 3000/3000A contained some semiconductors that are known to go "noisy" over the decades. It's probably worthwhile to just rebuild the board...there aren't that many parts to replace.

What is the signal meter showing when picking up a station(if its very weak no matter what antenna or station)? On my 5000x I found the tuner was getting 2x the voltage it should have. The cap and Zener diode were bad and nuked the 1st FET inside the tuning capacitor box, aka front end. Check the voltage supply to the front end. Aka tuner

It should be around 12v (note my cruddy red dot)

Does this have a separation adjustment on the rear panel? Might turn it back and forth some, see if it clears up the problem.