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SX-3800, SX-3900 tuner sens probs,and heat

wiseguy

wiseguy

Active Member
I am just curious if there are any FM sens issues with these 2 models..also heat build up..
I have a sansui qrx-7500a directly below this SX-3900..both tuned to the same station..(96.3)..the 3900 will hardly pick it up.the sansui picks up perfectly.I tried the same with my 3800,and its the same.(poor signal).i thought maybe i was in a blind spot or something..
to the left of these 3 units are a SX-980,and an SX-890,they pick up this station perfect.about the same levels also..
I guess my question is are there any service issues with the flourscan units?and FM sens?..I never touch the tuners when i recap any of my units..
had to ask..
also i had to measure the heatsink temp at high power with and without a fan on top....i used a fluke thermalcouple..wow does that heatsink give off heat at high power,seems like its dangerous..bias and all are fine..i never drove it up this high though..like to clipping..LOL..kinda fun to see if i would destroy outputs again....fan use does drop temp,a 12V fan running at 6 volts in my pics..
 

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I have a sx-3800 that seems to have tuning problems when it is next to certain other units. Oddly enough, other tuners seem to give the 3800's tuner fits. Try moving the 3900 somewhere else and see what happens.
 
my 3900 ran cooler at nearly constant full-tilt (and I had it there A LOT) than it did at idle.

probably had something to do with it blowing up.

I still want to get it fixed, but I have no money. bugger. damnit I like that thing.
 
For its sx-3900 not heat you have to adjust the bias voltage in 70mV, if you can not replace the resistor 143 and 144 to 1.2 k and readjust the tension to 70mv as the service manual. Hug
 
Side by side test of operating tuners can have them interfering with each other. The local oscillators are a very powerful local signal.

As the Germans and others in Germany found out during WWII. The authorities would DF the LO freq of the verboten stations (like BBC etc) and, uh oh, I hear trucks!! ("How did they know what we were listening to?????????")

Also why personal receivers weren't allowed shipboard, the uncontrolled LO's would radiate their position.

With radar detectors, the other's local oscillator gets into the rf input stage and causes a reduction in sensitivity.

The SUI's LO could be fritzing out the PIO's quartz lock circuits.

IF you can turn off the SUI momentarily, and there is no change, then I can revisit the issue.
 
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If your SX-3900 or SX-D7000 has problems in the fm? Low noise is noticeable on the speakers? too hot? put 2 capacitors 100nF 100v termimals 1.3 and 3.5 on the amplifier board and replace the resistors 143 and 144, 6.2 k to 1.2 k and reset the bias to 70mV as the service manual.
 
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Possibile solution

If your sx-3900 has problems in the fm? Low noise is noticeable on the speakers? too hot? put 2 capacitors 100nF 100v termimals 1.3 and 3.5 on the amplifier board and replace the resistors 143 and 144, 6.2 k to 1.2 k and reset the bias to 70mV as the service manual. Be careful.

DSCF3769.jpg


http://www.youtube.com/watch?v=T61MxjjImFg
http://restauravintage.blogspot.com/
 
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Shhhh, maybe nobody will notice for another 4 years.. :D

Then I won't have to argue his details.... They're not in any service bulletin I can find....
bypassing the power isn't harmful, but that resistor thing in the bias section can have ramifications that must be carefully calculated.....
 
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Sx-3900 "cold"

markthefixer said:
Shhhh, maybe nobody will notice for another 4 years.. :D

Then I won't have to argue his details.... They're not in any service bulletin I can find....
bypassing the power isn't harmful, but that resistor thing in the bias section can have ramifications that must be carefully calculated.....
Click to expand...


Hello Markthefixer a few days i send one email for you (dvnii@hotmail.com). I think it was a design error by Pioneer. I tried to remove the 6.2 k resistor but I could not reach them was below 70mV, so I put one of 1.2 k. The tension comes at 70mV near the center of trimpots. I put two capacitors 100nF between points 1-3 and 3-5 of the amplifier board thi strip all the anormal interference noise in FM, AM and residual noise on the speakers. This applies SX-3900 with modern board equal to the SX-D7000 I do not know if it serves the different boards. hug

DSCF3770.jpg


http://restauravintage.blogspot.com/
http://www.youtube.com/watch?v=T61MxjjImFg
 
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