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 Audio (record players, hi-fi etc)

Notices

Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

Closed Thread
 
Thread Tools
Old 5th Dec 2021, 3:20 pm   #1
STUDERUSER
Diode
 
Join Date: Feb 2021
Location: Stajerska, Maribor, Slovenia,
Posts: 5
Default Sony mhc-2700

Hello,
I have a mini hi-fi system SONY MHC-2700 from 1993. It served me well all the time, so I decided to try to extend its lifespan. I replaced rubber things like belts and pinch rollers (cassette deck), etc.
A big problem is the tuner (ST-H3700), which does not make sound in stereo mode. If you press the MONO button, then the sound appears, but of course mono. I’ve checked all the electrolytic capacitors that could be worn out due to age, but the ESR70 says none are critical. I suspect it could be a defective tuner chip (LA1851N).
The next problem is the brightness of fluorescent displays on all components. So I checked the voltages coming from the amplifier (TA-H2700) - this serves as a power supply to the other components - which are all, I think, within tolerance limits. Could the cause of poor luminosity be the age or wear of the gas in the fluorescent displays?
I would be very grateful for any hint.
Attached Thumbnails
Click image for larger version

Name:	IMG_20211204_212449.jpg
Views:	98
Size:	55.2 KB
ID:	247323   Click image for larger version

Name:	IMG_20211204_212223.jpg
Views:	66
Size:	78.6 KB
ID:	247324   Click image for larger version

Name:	IMG_20211204_212235.jpg
Views:	51
Size:	72.9 KB
ID:	247325   Click image for larger version

Name:	IMG_20211204_212658.jpg
Views:	57
Size:	41.1 KB
ID:	247326  
Attached Files
File Type: pdf sony_st-h3700.pdf (3.94 MB, 46 views)
STUDERUSER is offline  
Old 5th Dec 2021, 4:18 pm   #2
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
Default Re: Sony mhc-2700

Some vacuum fluorescent displays do go dim as they age. This particularly affects equipment which keeps the VFD powered up during standby (so as to show a clock, for example.)

Some mini systems can only be switched between mono and stereo using the remote control. Have you tried that?
paulsherwin is online now  
Old 5th Dec 2021, 7:17 pm   #3
Analogue man
Hexode
 
Join Date: Dec 2020
Location: Raunds, Northamptonshire, UK.
Posts: 339
Default Re: Sony mhc-2700

Quote:
Originally Posted by paulsherwin View Post
Some vacuum fluorescent displays do go dim as they age. This particularly affects equipment which keeps the VFD powered up during standby (so as to show a clock, for example.)

Some mini systems can only be switched between mono and stereo using the remote control. Have you tried that?
Or it may just be that the signal is so weak that the tuner is muting itself whilst switched to stereo.
Analogue man is offline  
Old 5th Dec 2021, 7:43 pm   #4
Lloyd 1985
Nonode
 
Lloyd 1985's Avatar
 
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 2,814
Default Re: Sony mhc-2700

Those displays just look like they are suffering from old age! If they were uniformly dim then it'd be a power supply issue, but those just look like old worn phosphor to me. As to the FM stereo fault, I also have a Sony tuner that suffers the same! Never did find out what was causing it, it wasn't poor signal in my case, as I tried one of those iPod FM transmitters right next to it, which does do FM stereo, but it still refused to pick it up in stereo. That particular unit does mute the audio on FM unless it's receiving a stereo transmission, or you press the mono button. Someone did suggest trying the 10.7mHz filters, as they can cause it, but i couldn't find any suitable to try it.

Regards,
Lloyd
Lloyd 1985 is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 3:46 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.