Sony ICF-2010 1st RF FET

Evaluation & Service 3 April 1994

Disclaimer-

No responsibility is assumed for any loss or damage resulting from the use of the information contained in this file. This file is not guaranteed to be complete or error free. It is the readers responsibility to evaluate the content, and its applicability to his/her situation. Electronic service carries certain inherent risks. It is the readers responsibility to determine his/her ability to perform the service described herein without damage to equipment, or risk of personal injury.

A Short Story-

Three or four years ago my wife and a close friend conspired to give me a Sony ICF-2010 for Christmas. It was my first decent radio, and it has given me hours of pleasure listening to the BBC, VOA, Radio Free America, local hams, etc. Still, I had to admit that there was surprisingly little out there for all the fuss people seemed to make over the SW hobby. On the other hand, the radio seemed to work pretty well, except at low frequencies.

Finally, having read about possible static damage to the 1st RF stage in the book Passport to World Band Radio, I became suspicious. I compared the performance of my radio to that of the friend who had recommended it. In a side by side comparison, there was no contest. My 2010 sensitivity was down 20dB or more at high frequencies, and even worse at low frequencies. Signals that lit his full bar graph S-meter barely registered on mine at all.

Now What?

The question now was, was it the front end? Or some other unrelated problem? Without access to a service manual or schematic, troubleshooting any more than a trivial problem would be hopeless. Since the Passport book identified Q303, the first RF JFET, as a possible problem, it seemed reasonable to check it. The easiest check was simple substitution with another device. Installing a 2N5457 (which has the same pinout) instantly brought the radio back to life, with lots of sensitivity and good sound quality! Measuring the old Q303 showed that it had become a low value resistor in all directions. Definitely toast.

How Can You Check Your 2010 & What is the Best Fix?

I put up with a poorly performing 2010 for several years, since I had no idea of what normal performance was. Hopefully this description will lead you to the answer is less time than I took. A correctly working 2010, with the RF gain at DX and the slide attenuator on the right side all the way up, should motorboat severely (oscillate) as you tune through 455 Khz. If you listen to the background noise, you should hear a distinct increase as you tune from 1620.1 Khz down to 1620.0 Khz. On a good day/night you should be able to just barely make out low frequency code beacons on 265 Khz and (louder for me) 345 Khz, depending on your location (I am in upstate NY). In any case, lack of low frequency signals is a definite indicator of problems. You should be able to get a good nighttime selection of clear channel AM broadcasters between 650 and 1000 Khz. Try for WSM in Nashville @ 650, WSAU in NY @ 660, WLW in OH @ 700, WJR in MI @ 760, and WCBS in NY @ 880. If you live in another area, you will have to get another list, but you get the idea. All this is with the normal internal ferrite rod antenna. Note that the radio disconnects the ferrite rod antenna if you plug in an external antenna. You will not get any low frequency stations (below about 1620 Khz) if anything is plugged into the external antenna jack. This is also the path for damage to Q303. Typically, static on an external antenna is what pops Q303. That is certainly how I damaged mine.

One more thing- interference is a serious problem. You may have to search your house for noise generators before you can listen to anything. In my case, a simple Sears humidifier was one of the worst culprits. The "low" speed setting is obtained via a standard light dimmer circuit, with no filtration. Adding the proper inductor to the circuit eliminated the noise. Any light dimmer (esp. on imported quartz halogen lamps) can be a problem. Many TVs also put severe noise on the line. Finally, the small energy-saving high frequency florescent bulbs are severe noise generators. You may have to start with everything in the house turned off. Try walking around with the 2010, using it as a noise meter at 1000 to 3000 Khz. It should lead you to the really bad stuff.

The 2010 is easy to work on (this section anyway), but if you are not reasonably experienced at electronic service, or if you don't have the right tools, TAKE IT TO SOMEONE WHO CAN DO IT RIGHT!!! The people listed at the end of this file can do it right. Don't mess up a great radio with sloppy service. Enough said. If you decide that Q303 may be damaged, and you want to replace it, here are some suggestions:

  1. The case comes apart easily, but don't forget the screw in the center of the battery compartment. Yes, you have to remove the D cells.
  2. Q303 is located on a small PC board, separate from most of the radio. The board has several very fine wires that attach to the ferrite loopstick antenna. Use extreme caution when lifting out the board- you do not want to stretch or break those wires! The PC board needs to be lifted and pulled back slightly so the external jacks clear the case. You can then fold it over to get access to Q303, which is clearly labeled on the board. Have someone hold the board while you work on it.
  3. Remember, many parts are static sensitive. Work on a grounded surface, keep the humidity high, and use a grounded soldering iron. The problem with static damaged parts is that they are often only degraded, and do not fail outright. That makes finding them difficult. The only smart solution is not to cause static damage in the first place.
  4. I strongly suggest installing a SIP socket at Q303 (a Samtec or similar), since it can easily be damaged again. Then you can simply plug in a fresh device without damaging the circuit board from repeated repairs. There is also less risk to the new JFET. If you do not have a three pin SIP socket, use three separate pins from a machined contact IC socket. Cut and form the leads of the new JFET to keep it close to the board. One end of the socket will be up against a resistor. You may have to trim the socket length slightly for a nice fit.

About Q303

Q303 is a Sony 2SK152 silicon N-channel JFET. They are manufactured in four gain groups. The 2010s I have seen use group 2. Thus, you want a 2SK152-2. The 2010 will work quite well with a 2N5457 as a substitute, but it does not have the gain or gate characteristics of the 2SK152. Sony only makes a few silicon JFETs, and they wouldn't bother making this one if it didn't have some unusually desirable characteristics. No other commonly available JFET I have tested comes close to the 2SK152, nor do any of the substitution guides list a substitute for it. That's not to say there isn't one, I just haven't found it yet. A 2N5457 will keep you running while the correct part is on order, but you really want the genuine item.

You can get SK152-2 JFETs, service manuals, Sony AN-1 active antennas, and a bunch of other good stuff from:

Universal Radio Inc. 6830 Americana Parkway

Reynoldsburg, Ohio 43068-4113

Orders: 800 431-3939 Information: 614 866-4267

FAX: 614 866-2339

I have no ties with this company, and am recommending them on the basis of one order. They were pleasant, knowledgeable, and did exactly what they said they would. They ship fast. Not bad in today's world.

 

From the Sony Discrete Data Book:

2SK152-2

Absolute Maximum Ratings

drain to gate voltage

15 V

source to gate voltage

15 V

drain current

50 mA

gate current

5 mA

junction temperature

100 degrees C

storage temperature

-50 to +120 degrees C

power dissipation

300 mW

Electrical Characteristics

   

min

typ

max

drain to gate voltage

Vdgo

Ig=10uA

 

15 V

 

source to gate voltage

Vsgo

Ig=10uA

 

15 V

 

gate cutoff current

Igss

Vgs=-7V, Vds=0V

 

-2 nA

 

drain current

Idss

Vds= 5V, Vgs=0V

9.5

 

42 mA

gate to source cutoff voltage

Vgs(off) Vds= 5V, Id=100uA

-0.55

 

-2.0 V

 

forward transfer admittance

|Yfs|

Vds= 5V, Vgs=0V, f=1Khz

21

 

30 mS

input capacitance

Ciss

Vds= 5V, Vgs=0V, f=1Khz

8

 

9 pf

Classification (Vds=5V, Vgs=0v)

Rank

Idss(mA)

1

9.5 to 14.8

2

13.4 to 21.0

3

19.0 to 30.2

4

27.4 to 42.0