Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Akai AT-27 tuner - FM Auto/Mono not working
Akai AT-27 tuner - FM Auto/Mono not working
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st May 2018, 12:11 PM   #1
qwer1304 is offline qwer1304
diyAudio Member
 
Join Date: Mar 2010
Default Akai AT-27 tuner - FM Auto/Mono not working

Got an Akai AT-27 tuner that works fine except for FM Auto/Mono feature.
When FM Auto is selected ALL stations are muted.
When MONO is selected all stations play fine.

I reckon FM Auto should select FM STEREO, if available, and MONO otherwise.

Any ideas?
  Reply With Quote
Old 21st May 2018, 12:15 PM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Akai AT-27 tuner - FM Auto/Mono not working
Low signal strength maybe ? Try it on a different aerial if possible.
  Reply With Quote
Old 21st May 2018, 12:17 PM   #3
qwer1304 is offline qwer1304
diyAudio Member
 
Join Date: Mar 2010
The thing is that with FM Auto engaged ALL stations are muted, while with MONO they all play without a problem. I expected FM Auto to switch to MONO if the signal strength was too low, NOT to mute.
  Reply With Quote
Old 21st May 2018, 01:31 PM   #4
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Akai AT-27 tuner - FM Auto/Mono not working
The exact nature of the muting could be tuner specific, but low signal strength would certainly be the first thing to eliminate for any fault like this.
  Reply With Quote
Old 21st May 2018, 02:52 PM   #5
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
What it should do may be described in the user manual.
  Reply With Quote
Old 21st May 2018, 04:07 PM   #6
GoatGuy is offline GoatGuy  United States
diyAudio Member
 
GoatGuy's Avatar
 
Join Date: Dec 2012
Location: SF Bay Area
Maybe I'm thinking like an electronic cow, but the description of the problem feels like a logic malfunction. To me. Sorry…

In order to keep consumer electronics “user friendly”, quite early in the development of FM radio receiver design automatic muting was added, gated off a “signal strength” assessor circuit, easily derived from the first IF mixer output. That way, as one would “turn the knob” (back when FM receivers had knobs that actually connected to variable tuning capacitors), the sound output would mostly be silence punctuated by near-to-well-tuned broadcast signal output.

Things became substantially more complicated with STEREO FM broadcasting; and with “channel capture” FM demodulator signal locking. But in the end, the output(s) of the IF mixer(s), the stereo discriminator and channel sideband separator, and those pesky front-panel buttons ("Mono / Stereo") were routed to a logic subcircuit that'd decide how to mute the channel, and when to let it pass thru. Signal “quality” of course.

So, given that, it feels like the logic subcircuit is either malfunctioning, or that the stereo 'signal strength' circuit isn't outputting '1' when it determines there is enough signal to warrant it. Either would result in the behavior indicated.

It is substantially LESS likely that you'd just happen to have a signal strength on all available channels, across the whole reception band that'd be low enough not to get at least a squeak out of one station or another. Seriously. Even in the “bad old days” when one had squirrelly twin conductor ribbon antennas that would inevitably come undone and fall off the antenna binding posts, even then, you'd still get a channel or three.

Just recalling,
GoatGuy
__________________
John Curl's Golden Rule…: 100 kHz bandwidth, 3 μs risetime, 100 W mean output, 100 V/μs slew rate, 2 Ω dynamic load, 20 amp min current source/sink
  Reply With Quote
Old 21st May 2018, 04:10 PM   #7
rayma is offline rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Quote:
Originally Posted by qwer1304 View Post
When FM Auto is selected ALL stations are muted.
When MONO is selected all stations play fine.
See if there is an adjustable muting control on the rear panel.
  Reply With Quote
Old 22nd May 2018, 01:24 AM   #8
ej25awd is offline ej25awd  Canada
formally hitachi_nut
 
Join Date: Jan 2007
Location: BC
Quote:
Originally Posted by qwer1304 View Post
Got an Akai AT-27 tuner that works fine except for FM Auto/Mono feature.
When FM Auto is selected ALL stations are muted.
When MONO is selected all stations play fine.

I reckon FM Auto should select FM STEREO, if available, and MONO otherwise.

Any ideas?
Your AT-27 is out of alignment. The quadrature detector coil T102 has drifted over the years and is no longer centered.

To fix this, you need a non-magnetic flat blade adjustment tool with approximately 1.5mm x 0.5mm tip. A bamboo chopstick that has one end shaped will work.

Tune to a strong FM station and slowly adjust T102 (see attached pic with the green arrow) on either direction until the station is no longer muted. You don't need to turn the ferrite core that far, only a few degrees. Note the old position with a marker so you can return it to the old setting if this doesn't work.

There is another adjustment for the FM "TUNED" sensitivity SR101 10k. Tweak this trimmer resistor if the above step didn't work. Same procedure, mark the old setting with a permanent marker first so you can revert to the old setting.

Good luck!

Akai AT-27 tuner - FM Auto/Mono not working-27-zero-adjustment-jpg
Attached Images
File Type: jpg AT-27 zero adjustment.jpg (29.8 KB, 104 views)
  Reply With Quote
Old 19th June 2018, 11:14 AM   #9
qwer1304 is offline qwer1304
diyAudio Member
 
Join Date: Mar 2010
I tried your suggestion (both options), but that did NOT improve the situation.

Here's what I noticed though:
With rabbit ear antenna, there ARE stations where the tuner locks (TUNED is lit) and STEREO reception is possible (albeit not very good quality).

HOWEVER, I noticed that the frequency that the tuner locks to is OFF relative to official frequency by several kHz.

BTW, after tweaking the pots as suggested and returning them back to their original position, I can no longer play ANY station in STEREO and scan would NOT tune to any station automatically.

Go figure

PS Anyone got a service manual of the AT-27 and is willing to share? Thx

Last edited by qwer1304; 19th June 2018 at 11:30 AM.
  Reply With Quote
Old 19th June 2018, 11:43 AM   #10
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
"Several kHz" does not matter; many stations are not exactly on their stated frequency for very good reasons. Many tens of kHz would matter.

If it is now worse than when you started that probably means that the cores you adjusted are not back in their original positions.
  Reply With Quote

Reply


Akai AT-27 tuner - FM Auto/Mono not workingHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Akai AA-V305 no tuner dogdays Solid State 1 12th June 2017 11:29 PM
Akai aa-m3 power not working eurosy Solid State 6 20th November 2016 06:11 PM
Turntable - auto doesn't working patknk939 Analogue Source 3 20th October 2008 02:12 PM
Auto soft-start for class-T amp not working Nuuk Class D 23 20th June 2006 07:12 AM
Akai AP 100C actually a P2 with auto return? G Analogue Source 0 15th September 2004 09:54 PM


New To Site? Need Help?

All times are GMT. The time now is 08:56 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki