UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 2nd May 2018, 2:22 pm   #1
bikerhifinut
Octode
 
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
Posts: 1,993
Default Mitsubishi M-F04 no stereo or tuned indicator

Hi,
I hope this is the right section as I wasn't sure if it was radio or Hi fi related.
I have been given a Mitsubishi midi sized hifi separates system of which one part is this M-T04 tuner. it's cleaned up very well and I would like to get it all working properly.
It tunes fine and brings up full signal strength on the LED bargraph indicator.
There is an issue though in that when switched to stereo it mutes.
There is also a green LED indicator to indicate a station is tuned in properly, this does not function at all in mono or stereo and i think the AFC is faulty too as it drifts off tune. The LED works as on Medium wave it lights up and the display backlight changes to green when a strong MW station is tuned.
It appears to be a traditional analogue tuner though I can't say if its varicap or capacitor tuned as I haven't opened it up yet.
I suspect it may be beyond my ability to repair this fault and if so I would rather pay someone to sort it. It promises to be quite a pleasant sounding unit and I noticed it was free from the whistles and "birdies" that my synthesizer FM tuners suffer from in this marginal reception area. That alone would justify my hanging on to it.

Thanks for any help.

Andy.
bikerhifinut is offline  
Old 2nd May 2018, 4:35 pm   #2
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,788
Default Re: Mitsubishi M-F04 no stereo or tuned indicator

A poor signal will produce these symptoms, but you say the signal is strong?

Decent tuners are 10 a penny so it's only worth spending time and money on it as an exercise.

Take the cover off and look for any obviously bad electrolytics, especially around the discriminator.
paulsherwin is online now  
Old 2nd May 2018, 5:19 pm   #3
Studio263
Octode
 
Studio263's Avatar
 
Join Date: Apr 2007
Location: Hampshire, UK.
Posts: 1,574
Default Re: Mitsubishi M-F04 no stereo or tuned indicator

A tiny tweak of the discriminator coil will fix this, you won't need to replace anything (especially capacitors).

A simple method is to tune to a strong station and then adjust the coil until the 'tuned' indicator comes on. The stereo decoder should then cut in, if it doesn't check the VCO adjustment associated with it.

The required adjustment is a fraction of a turn, don't go mad. Many Japanese tuners of this era seem to need this little tweak-up by now, its just about the only thing that goes wrong with them!

The cassette deck part of this, which is called 'System 4' (which is lovely - like a poor man's Aurex System 15 or Technics 'Concise Components' setup) is more problematic - the spool carriers are plastic mouldings which shrink around the brass hubs behind. They then fall off or get wonky, it seems to be a materials stability issue. Some creative lathework is required to fix this properly but it is worth the aggro - the deck base is die-cast and beautifully made and the heads are sendust - top quality stuff.
Studio263 is offline  
Old 2nd May 2018, 5:50 pm   #4
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,788
Default Re: Mitsubishi M-F04 no stereo or tuned indicator

Hmm... Not sure it's as simple as that, though the discriminator alignment being a bit out might explain the bad tuning indicator. You should still be able to tune by ear and get stereo. It will certainly do no harm to try adjusting the transformer core by a quarter turn though.

Bad electrolytics are quite common in hifi gear of this age, though I agree you shouldn't change them without a good reason.
paulsherwin is online now  
Old 2nd May 2018, 10:55 pm   #5
bikerhifinut
Octode
 
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
Posts: 1,993
Default Re: Mitsubishi M-F04 no stereo or tuned indicator

Would the discriminator coil be responsible for a lack of AFC as well as not unmuting the tuner when locked on to a signal? Certainly there is not a flicker from the green tuning led. I get a full set of bars lit up on the local FM stations so I imagine theres enough to get some sort of stereo signal.
I think I might enlist the help of someone to look at it as I am loth to disturb what I don't really understand, It's got to be fixable and its a lovely thing to my eyes and a proper capacitor tuned analogue tuner. I find these to work better in marginal signal areas for some reason. My denon and Arcam digital tuners suffer from digital noises whereas this one doesn't seem to.
I take your point about FM tuners being ten a penny Paul, but with respect that's not the point with preserving and refurbishing vintage equipment to me. these items are interesting in their own right to me. And we still listen to FM radio here!

The info on the cassette deck is noted, I have a separate thread running on this. Again I am willing to do a certain amount of stripdown to replace the obviously perished gooey belt but any sort of machining/engineering is beyond my capabilities or workshop tools.

Thanks so far gents.

Andy
bikerhifinut is offline  
Old 3rd May 2018, 9:52 am   #6
Studio263
Octode
 
Studio263's Avatar
 
Join Date: Apr 2007
Location: Hampshire, UK.
Posts: 1,574
Default Re: Mitsubishi M-F04 no stereo or tuned indicator

Where a "tuned" indicator is fitted to a Japanese tuner of this era the stereo decoder is nearly always gated out until it is lit - not 'tuned' - no stereo. It is important to get this aspect working first.

As this unit is part of a very attractive little system simply replacing it with another one of a different type isn't really an answer.
Studio263 is offline  
Old 3rd May 2018, 10:43 am   #7
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,788
Default Re: Mitsubishi M-F04 no stereo or tuned indicator

It's certainly worth tweaking the discriminator transformer core and seeing what happens - this will only take seconds and is completely reversible if you make a note of the position of the core before you adjust it. You do need to identify the right transformer though. A service manual will make this easy, or one of us can probably guide you if you post a closeup photo of the PCB.

I didn't mean to discourage you from trying to fix this if you particularly like it for whatever reason.
paulsherwin is online now  
Old 18th Jun 2018, 9:37 pm   #8
Studio263
Octode
 
Studio263's Avatar
 
Join Date: Apr 2007
Location: Hampshire, UK.
Posts: 1,574
Default Re: Mitsubishi M-F04 no stereo or tuned indicator

I've just had this unit on my bench for repair. It was the discriminator coil, just a little tweak and off it went, stereo and all.

The failure of low power components in Japanese equipment of this type and era is very unusual, it pays to discover the basic cause of any fault before changing anything. High precision circuits need careful adjustment, but simple things like dirty switch contacts account for the great majority of problems.
Studio263 is offline  
Old 18th Jun 2018, 11:19 pm   #9
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,788
Default Re: Mitsubishi M-F04 no stereo or tuned indicator

Glad to hear it's sorted.
paulsherwin is online now  
Old 19th Jun 2018, 6:24 pm   #10
bikerhifinut
Octode
 
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
Posts: 1,993
Default Re: Mitsubishi M-F04 no stereo or tuned indicator

Thank you very much Tim.
It's a really nice piece of kit and I look forward to getting it into the system.
My experience with "Old fashioned" analogue tuners is that they seem to work better than modern synthesiser jobs in difficult reception areas like mine.
If its still a bit marginal off the 3 element Antiference you will likely see me ask for aerial advice on a new thread!
Thanks muchly Tim.

Andy.
bikerhifinut is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 3:37 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.