2230B low FM sensitivity

ckuecker

New Member
Hello,

I am working on a 2230B. Recapped it, it sounds great as an amplifier.

FM works, but has horrible sensitivity, and no stereo indicator even with strong stations. Has anyone had similar problems?

I recently recapped a 2230 - I know it's a completely different arrangement, but FM stereo works as I would expect, so it's an issue in the 2230B for sure.

I don't have a dedicated FM signal generator. Has anyone done an alignment on one of these using a FM stereo converter for a CD player? I have one of those.
 
Did it operate properly before you worked on it? If so check your work.
I have never found a tuner that was extremely weak due to misalignment, it was always due to a fault somewhere.

I'm not a big fan of alignment without a good understanding of tuner theory, much hands on experience and the required test equipment, but this thread has some information.

Tom
 
The unit came to me from a customer. I replaced all the electrolytics and set up the amplifier, and found the FM issue while testing. I didn't test before replacing the caps, but none of the caps should have affected alignment.

I tested the receiver with my service monitor's generator - full quieting at around 100 uV. I've tuned up many two-way radios and typically see sub-micro volt sensitivity. My first thought was the input JFET is not working, or the alignment is way off. I don't want to poke into the tuner without knowing I can get the correct transistors.
 
Also, the FM mute shuts off everything regardless of where R253 is set. Leads me to think that a transistor is bad somewhere. The signal strength meter barely moves off the stop with a very strong signal.
 
Is there an antenna hooked up in the back? You'll have reception like you mention without one. An el cheapo "T" dipole will work fine most of the time.
 
I tried a dipole and a vertical with a ground. The 2230 I also worked on picks up FM stereo with no trouble and no antenna.

Driving the 75 ohm input from my signal generator shows terrible sensitivity, and the mute function mutes everything, even a strong signal from the generator. There's either a bad transistor or something in there, or the alignment is really off.

For what it's worth, the 19 kHz signal is on the money in the decoder.

I'd start trying new transistors, but the original parts are really hard to find, and I can't find any cross-references to 2Nxxxx parts. Is there a source for the 2SK19(Y), for instance?
 
According to a SM there is one switch at the back for the antenna attenuation, see if it is on out position.

edit: Oops! I looked for the 2230 sm, I don't know for "B" version... Sorry.
 
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No switch. Perhaps this is a later / earlier 2230B?

Yes, the 2230 has a pot for muting.
 
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The unit came to me from a customer. I replaced all the electrolytics and set up the amplifier, and found the FM issue while testing. I didn't test before replacing the caps, but none of the caps should have affected alignment.

I tested the receiver with my service monitor's generator - full quieting at around 100 uV. I've tuned up many two-way radios and typically see sub-micro volt sensitivity. My first thought was the input JFET is not working, or the alignment is way off. I don't want to poke into the tuner without knowing I can get the correct transistors.

Did you measure the AGC voltage (J103) to see if it is varying as you tune through a strong station, or as you vary the output of your generator?

100uV is a lot for full quieting, a few uV should get you 30dB of quieting, 10uV should get you around 50dB. If your service monitor will do level calibrated 10.7MHz, you could see what level it takes to get full quieting when you inject a signal into the IF input of the P200 IF amp (J201). The difference between the IF level and the RF level should give you the gain of the front end. Normal FE gain is around 30dB.

You could sub in the tuner IF output from the 2230, disconnect the cable from J104 on the 2230, disconnect the cable from J201 on the 2230B, then connect J104 on the 2230 to J201 on the 2230B. This will tell you if the problem is in the front end or the IF strip.

You are wise to not jump into replacing the FE transistors until you are sure where the problem lies.

Tom
 
J103 shows voltage starting at about 250 microvolts at the antenna input at 109 MHz. It goes negative with respect to ground as the level increases.

I get full quieting at 10.7 MHz to the IF with 90 uV input.
 
It appears that the AGC is working. I believe you have a problem with the front end. It is getting power supply voltage, right?

Did you try to sub in the one from the 2230?

What are the voltages on H101, 102 and 103?

Tom
 
Definitely getting power. When I probe with the DVM, I get big changes in audio, including signals that appear out of band, such as CW code. I'm going to look for cold solder on the tuner first.
 
Tuners are very sensitive to signal injection.
Did you try to sub in the one from the 2230? That would be my first trouble shooting technique after verifying the tuner was getting power.

Tom
 
CW code is Morse code.

CW stands for Continuous Wave.

And the Code means Morse code.

It was/is a method, similar to the telegraph of the old west that allows the transmission of text and numbers using radio waves. Basically the CW or continuous wave radio signal is turned on and off in predefined patterns, each individual pattern of dots and dashes ( the signal turned on for short, the dash and longer periods of time, the dash) representing a letter, number or punctuation mark.

The short and long signals are called dits and dahs by those of use that use this mode of communication.

This example is used for radio communication and is not the same as what was used by the telegraphers of the old west.
 

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