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A lot of people confuse this with Volume mute which shuts down the volume so you can talk to someone. FM MUTE IS DIFFERENT. The FM Mute only mutes the interstation hiss between stations, it doesn't mute the sound off. Turn it on and put it in FM. With the Mute OFF turn the tuning knob slowly up the dial, you'll hear stations come inand out with a fair amount of hiss between. Now turn it on. As you go up or down the dial, at a preset signal level, You'll hear a station come in all of a sudden (like a light switch was turned on) tune up to center and then back down again to a preset level internally, and shut off the signal until another station's signal level trips the mute back off. It mutes or kills the interstation hiss and other noise (like a very weak station) below a preset level in the circuitry.
Thanks for the response. What I am referring to is what you are describing, the interstation hiss. Upon further investigation it is working, but the muting is just barely noticeable. Still has lots of annoying noise between stations. I have an Akai AA-1050 receiver that has a mute adjusting pot on the faceplate. Very nifty.
It appears that the mute function is handled on both the MPX board (W13-021) and the IF board (W12-020). The switch only cancels the mute function performed on the MPX board The mute signal from the IF board has to originate from the third stage IF amplifier. The stage is tuned by core adjustment in T203 as part of FM alignment. Proper adjustment of this requires a signal generator and oscilloscope.
Short of full alignment, the signal at the MUT pin on the IF board can be monitored with a voltmeter to observe any signal transition when tuning from a strong FM stereo signal to dead air. If the signal does not change appreciably, from about 0.5V to 2V, there may be alignment required. If the signal DOES change there may be a problem on the MPX board with one of the switching transistors (Q6/Q7), connections, or other problems. One adjustment for FM Stereo threshold is at VR702 (marked VR2 on the MPX board) to adjust the sensitivity. If you note the original position carefully you may want to attempt adjustment of that if all other items check O.K.
Short of full alignment, the signal at the MUT pin on the IF board can be monitored with a voltmeter to observe any signal transition when tuning from a strong FM stereo signal to dead air. If the signal does not change appreciably, from about 0.5V to 2V, there may be alignment required. If the signal DOES change there may be a problem on the MPX board with one of the switching transistors (Q6/Q7), connections, or other problems. One adjustment for FM Stereo threshold is at VR702 (marked VR2 on the MPX board) to adjust the sensitivity. If you note the original position carefully you may want to attempt adjustment of that if all other items check O.K.
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Thanks for the info Watthour. The muting is working much better now, however I don't know what I did to fix it. Maybe I repaired a bad solder joint while checking the components in that area? Measuring 0.5V to 1.26V at the MUT pin.
Now it time to try and figure out why there is a faster rate of volume change, when the volume knob is turned up past the 8:30 position. Same in both channels. Gets loud real quick.
Now it time to try and figure out why there is a faster rate of volume change, when the volume knob is turned up past the 8:30 position. Same in both channels. Gets loud real quick.
If you are using a source that has a high voltage output (>1VDC) the sensitivity of the volume control is extremely touchy. CD Players, IPODs, MP3 players, et al (basically anything digital) has a way higher output voltage than the receiver input sensitivity is set up for. Most receivers and amps of the ERA had line level sensitivity of 200mv to 450mv. Plug it in to a unit that puts out 2 volts and instant overload. I would try turning down the volume on the source 1st, then set your main volume on the receiver to where you want it and are comfortable with and then adjust the source volume up to that level.
If this is the case, you can also get inline attenuators to drop the voltage going in to your 1000TW. 3db to 5db to start with.
If this is the case, you can also get inline attenuators to drop the voltage going in to your 1000TW. 3db to 5db to start with.
Thanks Larry, good info. I am not plugging into the receiver another device though, just using the FM. I did change all the electrolytic caps and transistors on the power supply, main amp, control, amp, and head amp. Did not change anything on the FM or MPX unit. Worried that I might then need a realignment, which I do not have the equipment to perform, nor want to spend the money for someone else to do it. My first time doing all this work. This receiver was in storage for quite some time, and I can not remember if it had this volume sensitivity issue existed before I replaced all these components.
OK. Just wanted to make sure you weren't confused between FM Muting and Volume muting (-20db or such) as most new guys are with old gear. Getting the alignment done will ensure that the RF and IF stages of the tuner are at peak performance levels and the same for the MPX. Some manufacturers MPX are very sensitive to RF & IF stage tuning and that includes the Muting. It's kinda like getting tires for the car and not getting it aligned to allow the tires to perform at their best and last longer. Most places I know in the Northeast charge about $100 for a complete RF/IF/MPX alignment as long as there are no other problems. I would imagine Calif, would be a bit higher. check with Fred Longworth @ Classic Audio repair in San Diego (www.repairaudio.com He's been on AK close to when it 1st started up and is a fountain of knowledge. Here's a newspaper article on him from 2013.... http://sdcitybeat.com/article-11383-meet-the-no-nonsense-man-behind-classic-audio-repair.html