Ebay Sansui 7900Z Volume not working correctly

Most of the gears in that motorized volume assembly are plastic. I lubed mine with a short burst of Remington gun oil and it moves very smoothly now. Sound like you have some junk or corrosion somewhere in the signal path. Liberal application of Deoxit may be the answer.
 
So obvious I hate to even suggest it, but make sure the tape monitor is not on. These models don't have preout/main in facilities, so that won't be an issue.
 
The volume control is not the problem see exert form Post #20
Yes! :thumbsup: I wanted to check out the volume control first so I pushed on the UP button and the motor started turning easily.... it kept turning as long as I applied pressure to the button.. Pushing the DOWN button also turned the motor in the reverse direction and the associated tuning cord. Even the bargraph shows increasing and decreasing volume levels. Tuning to a local radio station caused the tuning bar increments to increase to 5 bars so the tuner is working good as well. BUT....with volume maxxed out on the bargraph there was only faint music coming from both L/R speakers. Looks like the volume problem wasnt in the volume button gizmo but rather somewhere downline from there..
 
The volume control is not the problem see exert form Post #20

Yes you are correct the volume control wasn't the problem.:thumbsup: Fortunately I found what was causing it..... I'm quite embarrassed to say the problem was in the "knobology". On the far right there's a rectangular button labelled 'FM Mode/FM Muting' that was in the 'out' position which means it was muting the audio! I have to say the functions of some of the push buttons on this model are a bit confusing and take some getting used to.. it seems they do the opposite of what you'd think they would. It apparently fooled the eBay seller too as he sold me the unit with a volume problem... at a discount.:dunno: No complaints here though!... I was getting ready to troubleshoot the circuitry when i inadvertently pushed the perpetrating button in (volume at 80%) I literally jumped our of my freaking chair it was so damn loud. I just finished refurbishing a set of Advent original loudspeakers with 10" woofers and was using them as test speakers... well I must say they passed the test with flying colors!

Most of the gears in that motorized volume assembly are plastic. I lubed mine with a short burst of Remington gun oil and it moves very smoothly now. Sound like you have some junk or corrosion somewhere in the signal path. Liberal application of Deoxit may be the answer.

Thanks for the tip I gave them a shot of bike lube and they turn a lot smoother and easier now.:thumbsup:
 
Here's some jpg's of the latest addition to my household... sorry for the double images. Sansui.7790Z that I purchased on eBay $150 with a "no volume control" problem that turned out to be caused by a button in the wrong position. Shot some deoxit into the pots to fix a scratch balance adjust. The unit so far works excellent with one exception, that being the tuning search feature doesn't lock on to good stations but just keeps searching until I switch it back to manual search. Other than that this baby is working great!
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On the far right there's a rectangular button labelled 'FM Mode/FM Muting' that was in the 'out' position which means it was muting the audio!
If the FM muting is muting the Audio, then it is not functioning correctly. The function of FM muting, is to mute the noise between the stations, so that when you are tuning, the only audio that passes, is the actual radio stations.
If its muting the radio stations, then it may need adjusting.
 
If the FM muting is muting the Audio, then it is not functioning correctly. The function of FM muting, is to mute the noise between the stations, so that when you are tuning, the only audio that passes, is the actual radio stations.
If its muting the radio stations, then it may need adjusting.

I see... good to know and makes sense considering it fails to lock during a tuning search... probably related to the same problem.
 
Decided to take a closer look at the circuitry involved with the muting. I spent most of the day yesterday figuring out the schematics and trying to find where they hid the 42 pin PLL synthesizer control IC (TC9140P) aka fIC1. Ended up having to take the face, tuning scale, light bar etc off just to get to it. The first thing I noticed is the schematics dont jive with what is actually there on the board. Tomorrow I'll try to trace the high/low circuitry thats supposed to mute the outputs of the tuner... The FM stereo locked LED is also not lighting up when obviously strong clear FM stations are playing over the speakers.
One thing thats a little confusing is how the tuning board is divided into AM and FM sections with a zig zagging line on the board. Looks like they combined some components to work in both AM and FM??? For instance on the schematics both AM and FM sides have an eQ4 and an fQ4 but there's actually only one on the entire F-3300 board. Needs further study...
 
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