AM正常 FM收到很小声要调整FM鉴频中周吗？

tellalie

一个JVC的收音头 FM用HA1137+HA1196
AM正常，FM声音开到最大很小声，查了电路都正常，信号强度1格都没有，AM中国之声都有4个。
最近看了论坛的贴，说是鉴频中周里面电容的问题，我就拆出来，酒精擦洗了电容焊回去，用螺丝刀调了中周，顺逆时针方向均试过没啥区别，奇怪了，我发图你们看看该如果整吧？我试过输入正常IF信号，只是变到2格，但是音量没什么改观。




顺便问一下这个板子是干嘛 有2个可调电容，

定鱼哥

不一定只是鉴频中周的问题，如果年代久远，可能还需要统调，比如混频中周，放大电感等等。也不排除电路其他故障

tellalie

汪洋中的船

参考这个，带通滤波器不良灵敏度也低。
https://www.jdbbs.com/thread-8268278-1-3.html
http://blog.sina.com.cn/s/blog_14ee8493c0102w7kn.html

tellalie

汪洋中的船 发表于 2020-2-24 11:30
参考这个，带通滤波器不良灵敏度也低。
https://www.jdbbs.com/thread-8268278-1-3.html
http://blog.sin ...

我就不知道为啥本地强台一个信号都没有 里面FM电路的中周就一个 其他好像塑料电感

tellalie

汪洋中的船

tellalie 发表于 2020-2-24 23:30

调节这个电感试试能否改变状况。

ye123

汪洋中的船 发表于 2020-2-26 17:03
调节这个电感试试能否改变状况。

电感一般情况下最好不动.......出现这种问题一般都是铰链电容的问题多....

tellalie

汪洋中的船 发表于 2020-2-26 17:03
调节这个电感试试能否改变状况。

调了没啥变化啊  人家说这个中周上下均可以调节 难不成拆出来直接扫频调整更加好？

tellalie

hgrrr 发表于 2020-2-24 08:59
检查一下鉴频输出的交联电容，这个很容易疏忽！！换一个好的试试，亲身的经历！

我把电路图放上来 是不是HA1137的第六脚输出接着的电容啊？
这个我来换了试试看看

tellalie

汪洋中的船 发表于 2020-2-26 17:03
调节这个电感试试能否改变状况。

我来试试这个电感 就是总觉得信号表的强度太小了
确实信号表有点变化，螺丝刀进去那一下就变大声点点，我正负5圈试试了，反正螺丝刀拿出就小声了
然后我就调橙色电感，现在死马当活马医了，本地最强电台已经能达到2-3格的强度了

tellalie

6-（1）FM Section
Note：Keep the muting push button off during this procedure.
Discrimintaor，Center Meter，Distortion and Signal Gain


1.Connect an RF generator,1kHz modulation and 75kHz deviation, to the antena terminals on the rear panel through a dummy antenna.
2.Connect an oscilloscope,distortion meter and AC VTVM to the Rec.Out Jacks on the rear panel.
3.Connect a DC VTVM to Tab No.107(Positive)and ab No.106(Ground)
4.Tune to a frequency where there is no broadcasting.
5.Adjust the bottom core of T101 so that the DC VTVM indicates"0"(zero)
6.Set the generator to 98MHz.
7.Set the dial pointer to 98MHz.
8.Adjust the top core of T101 so that the  distortion is minimized at a value less than 0.4%.

Tracking and Sensitivity

Precaution：No adjustment is required.The tracking and sensitivity has been adjusted properly and completely at the factory.
If any special reason occasioned，take the following poriced

Low Frequency
1.Connect an RF generator to the antena terminals on the rear panel through a dummy antenna.
2.Set the Rf generator to 88MHz.a modulation of 1kHz and a deviation of 75kHz， to provide an input of 2uV.
3.Connect a VTVM and an oscilloscope to the Rec.Out Jacks on the rear panel.
4.Set the dial pointer to 88MHz.
5.Adjust three coils L103，L102 and L101 in the tuning gang to maximize the output

High Frequency
6.Set the Rf generator to 108MHz.a modulation of 1kHz and a deviation of 75kHz， to provide an input of 2uV.
7.Set the dial pointer to 108MHz.
8.Adjust FM trimmers TC101，TC3 and TC1 in the tuning gang to maximize the output

Multiplex and Stereo Separation

Multiplex
1.Set a stereo signal generator as follows：Modulation frequency 1000Hz，Deviation pilot 7.5KHz，Main and Sub.67.5kHz .Connect its outputs to an RF generator.
2.Connect an RF generator to the antena terminals on the rear panel through a dummy antenna.
3.Connect a VTVM and an oscilloscope to the Rec.Out Jacks on the rear panel.
4.Set the Rf generator to 98MHz and a output of 1mV.
5.Set the dial pointer to 98MHz.
6.Connect a frenquency coynter to Tab No.109
7.Switch off the pilot signal of the stereo modulator.
8.Adjust R129 so that the frequency counter indicates 76kHz（±0.05kHz）

Stereo Separation
9.Switch the selector of the stereo modulator to left channel modulator.
10.Adjust R134 so that the output of the right channel is minimized.
11.Switch the selector of the  modulator to right channel is minimized.
12.Adjust R134 so that the output of the left channel is minimized.
13.Set R134 to average，if the separation of right and left are different.



手册上的FM调机说明

yeppdai

楼主还是从前级开始查起吧，一步一步来，不建议随便调中周，S曲线有了仪器都很难调的。

tellalie

yeppdai 发表于 2020-2-28 16:30
楼主还是从前级开始查起吧，一步一步来，不建议随便调中周，S曲线有了仪器都很难调的。

我现在是FM声音小的可怜啊AM正常得很，今天调了几个把信号增加到3格了，中周换了电容，中周上下调了听起来没啥变化了，反正我都没办法找原因