Previous: ICF-7601, ICF-7600DA/ICF-7700

Page Contents

  1. ICF-7600D and ICF-7600DS a.k.a. ICF-2002 and ICF-2003
  2. ICF-7600A/ICF-7600AW
  3. ICF-7600/ICF-7600W
  4. A few 7600 series receivers compared
    1. Feature comparison of ICF-7600D(S), ICF-SW7600 and ICF-SW7600G(R)
    2. Shortwave gain stage / AGC overview
  5. Receiver utilities
    1. The AN-LP1 active antenna
    2. Misc. headphones

ICF-7600D/DS (ICF-2002/2003) section

[ICF-2002/ICF-7600D pic] [ICF-7600DS pic]
The original ICF-7600D = ICF-2002 ([5]) and the ICF-7600DS = ICF-2003 ([6]).

General information

Pros

  1. First digital receiver in this size
  2. Good performance for its size in 1983 (it was slightly superior to the ICF-2001)

Cons

  1. No battery indicator
  2. No stand on the back (unlike later models)
  3. Believe it or not, the loose contact problem (with the power supply connector) of the ICF-SW7600G already existed with that model! It can be fixed the same way.
  4. Selectivity (at least on earlier models) isn't that great by today's standards, neither is the noise level or susceptibility to overload – but then the set was introduced in 1983... It's still a nice SWL receiver for travellers, but certainly not a DX machine.

Reviews

  1. Martin Bsch zum ICF-7600D

Additional information

Operating manual

Manual downloads at Sony – ICF-SW7600GR, ICF-SW7600G, ICF-SW7600, ICF-7600D

A manual in Dutch, German and Swedish is available at RigPix.

My take on the ICF-7600D

You can read about my findings while briefly checking out an ICF-7600D of the newer variant (with narrower IF filter) on my receiver review page.

Links

Yahoo! Groups:

Specified power consumption

Total current spec from the schematic (with minimum output, I suppose):

The DRM mod document talks about a current draw of 45 mA in FM and 50 mA in AM (55 mA in AM with DRM downmixer installed). Maybe later models were improved in this regard?

Servicing and internals

Service docs

Bernhard Weiskopf kindly scanned and converted the schematic of the ICF-7600DS (int'l version), as of 1987.11.

A partly complete scan of the ICF-7600DS service manual (containing 16 of 30 pages) can be found in the '7600GR' group's files section; local mirror.

If you need a service manual in paper form, there are various sources that sell 'em. I have mentioned a local one in the misc links section.

Opening the 7600D

Opening a 7600D has proven to be not entirely trivial. Here's the trick, as posted on 7600group:

From: h van vliet <vanvliethc@y...>
Date: Mon Feb 21, 2005 10:14 am
Subject: Re: [7600group] Re: IDF-7600D - How do I open it?

To open my ICF-7600D I loose (and remove) the two black screws on the L and R top and the two brass screws (one in each battery compartment). Then, because of a lip on the right lower side, I open the backside turning it like a page from left to right. No problem. Furthermore, like with laptops a strong thumbnail is an indispensable asset for loosening latches.

Hein van Vliet

ICF-7600D/ICF-2002 versions

From: "crabtreejr" <crabtreejr@...>
Date: Fri Jun 10, 2005 4:11 am
Subject: ICF-2002 circuit changes

Hello All

I have recently obtained an original of the ICF-2002 service manual (9-951-280-11, 1983) and a photocopy of supplement No. 1 (9-951-280- 81, October 1984). This supplement was issued to cover two updates: additional color variation, and circuit variations to reduce drift of the second oscillator. I believe that this supplement covered the infamous warranty changes which Sony made to the ICF-2002 starting late in 1984 or early in 1985. If anybody has further information, please let me know.

The ICF-2002 and 7600D are considered to be identical, as are the updated versions, ie the ICF-2003 and 7600DS.

1. Additional color variation.

The original model was issued in a silver case. A black case was introduced. The following parts were added (silver part no. then black part no):

15 Knob (fine) 3-891-803-00 3-891-803-11
20 Button(E) 3-891-808-00 3-891-808-11
25 Strap, Hand 3-891-813-00 3-891-813-11
29 Lid, battery 3-891-817-00 3-891-817-11
30 Knob (vol) 3-891-818-00 3-891-818-11
31 Knob (tone) 3-891-819-00 3-891-819-11
32 Knob (mode) 3-891-820-00 3-891-820-11
33 Knob (sens) 3-891-821-00 3-891-821-11
42 Chassis 3-891-843-00 3-891-843-11
46 Holder 3-891-872-00 3-891-872-11
48 Lid (rear cabinet) 3-891-874-00 3-891-874-11
56 Screw 7-685-152-14 7-685-152-19
60 Front panel X-3891-809-1 X-3891-831-1
63 Label 3-891-871-00 3-891-871-11
2. Circuit changes

To quote the Sony supplement: "The circuit has been changed to reduce the drift of the 2nd local oscillator and location of some parts on printed circuit board has been changed."

The ICF-2002 circuit diagram was re-issued in the supplement. In the original the horizontal position was indicated letter, and the vertical position by number (as in an Excel spreadsheet). In the supplement and for the for the ICF-7600DS the notation was reversed.

The component changes were:
(schematic location original / supplement)

Five of the ten components which were changed were on the antenna board. The easiest way to tell if one has an original or updated ICF- 2002 is to look at R168. It is on the antenna board just to the left of the top left hand corner of the external antenna socket. It should be possible to tell if it is 33 ohms (orange-orange-black-xxx) or 220 ohms (red-red-brown-xxx).

3. Discrepancies

There appear to be some discrepancies in the manual and supplement which I have for the ICF-2002:

R66

The original circuit diagram shows R66 connected between the source of Q11 and ground. The original PCB layout shows it connected between the source of Q11 R64/C52. This is the way in which appears in the cct diagram in the supplement. I checked my non-early ICF- 7600D and it is wired as per the supplement. Interestingly the manual for the ICF-7600DS (9-952-946-12) shows the circuit as per the ICF-2002 original manual, but the PCB layout (different from the ICF-2002) is for the circuit in the ICF-2002 supplement no. 1.

C43

This component is in the drain circuit Q7, the AM rf amp The cct diagram for the original ICF-2002 manual and supplement no. 1 show C43 connected between cathode of D16 and drain of Q7. However the PCB layout shows C43 connected between the cathode of D16 and connection of C48 to C49.
The cct diagram in the ICG-7600DS manual shows the latter configuration.

D209

Looking at the PCB layout, it is not clear to me why this component exists, as it connects between two points on the same PCB track. D209 is not shown on the parts list or cct diagram for the ICF- 7600DS, but still appears on the PCB layout.

keyboard PCB

I looked at the keyboard PCB on my ICF-7600D. C205, C207 and C217 were mounted on the track side of the PCB, not as per the ICF-2002 manual. What was marked as C222 on the PCB appeared to be C224.

4. Conclusions

Having documentation with apparent discrepancies makes tracking the history of the models 'challenging'.

The component changes shown in section 2 appear to have been carried over to the ICF-7600DS along with a small number of additional component changes I shall write a separate note at a later date describing these. An updated ICF-2002 and ICF-7600DS are essentially the same radio.

Thanks to Rick in Atlanta for the ICF-7600DS manual.

I would welcome any comments.

73 John KC0GGH
crabtreejr at aol dot com

On excessive battery drain

If you have an ICF-7600D(S)/2002/2003 draining the batteries even when off, this might help (again, from 7600group):

From: "Bernhard Weiskopf" <bweiskopf@g...>
Date: Thu Oct 2, 2003 10:17 pm
Subject: Re: ICF7600D/ICF2002 question

Hello together

I have a service manual of the ICF-7600DS. Due to its age it is in paper shape.

In off mode there is working a 3 V linear regulator.
The main IC PD1706G-511 or -519 (from NEC) contains the 10 preset memories which are buffered by the 3 V "computer battery" as well as by the 6 V "radio battery" (via the a. m. 3 V regulator). So you can change one of these batteries without loss of memory.

The 3 V regulator draws continuously about 30 A out of the 6 V "radio battery", not more.

The clock module is powered only by one cell (1.5 V) of the "computer battery".

While the off-state current is about 30 A (@ 6 V), the on-state current is 70...80 mA (@ 6 V and low volume).

He measured 10.7 milliamps with the radio turned off and of course 75 milliamps when it is turned on.

10.7 mA off-state current is too much. 75 mA in on-state is ok.

May be one of the switching transistors is damaged so it cannot switch-off anymore.

Looking at the circuit diagram I assume as critical part the swichting transistor for the AF output power amp (PC1212C).
If a short circuit to ground occurs at the earphone jack, I guess an overload condition at the switching transistor.

Switch off the radio (tone switch to music) and hold your ear directly at the loud speker. Can you hear some low noise?
If yes, change the damaged Q32 (2SB1013).
(Other test: You must hear a noticeably pop-up noise during switching on (volume = min.). In case of a damaged Q32 there will be no pop-up noise.)

Good luck!
Bernhard

Audio frequency response

Via PM, Bernhard told me that he had, among other things, changed the frequency response of the audio amp because originally it was too muffled.
A circuit simulation via LTspice had shown the following -6dB points:

The lowest frequency the speaker can reproduce is about 250 Hz.

The front end

The ICF-7600DS/ICF-2003 uses a front end similar to later digital models (ICF-SW7600 upwards), but with 2SK152-2 FETs.

ICF-7600A(W) section

[ICF-7600A pic]

General information

Pros

  1. Being a very sensitive and quite selective dual conversion set, the RX was superior to most other travel portables on SW available at that time – in fact it's far from bad today.
  2. Batteries lasted forever – about 40 hours.
  3. Fairly good dial accuracy (about as good as on the ICF-7601 on my ICF-7600A), even though on some bands there are larger unmarked ranges where you have to extrapolate.
  4. Good craftsmanship.
  5. Good AM audio with little excessive hiss, good speaker sound.
  6. Decent FM sensitivity and selectivity.

Cons

  1. Limited band coverage (no 22m, no 60m, top 300 kHz of 19m band missing).
  2. Although better than the ICF-7601, still rather susceptible to intermod due to the wide 1st IF on SW (a weak spot of the concept).
  3. No stand on the back, which would have been very advisable since the acoustic design requires that the speaker be able to "breathe" on the back.
  4. Some tuning backlash.
  5. Mediumwave shows a few spurious shortwave stations.
  6. The speaker is easily damaged when you open the radio, being glued to the front of the case – so beware. (My uninformed guess was that this was done for better sound, and indeed this is one of my best-sounding units with a 3" speaker.)

Additional information

My take on the ICF-7600A

You can read about my findings with an ICF-7600A / AC-456C combo on my receiver review page.

Servicing and internals

Service docs

A while back I scanned the relevant pages from the ICF-7600AW service manual. You can now download the result here.

Tips

ICF-7600(W) section

General information

Pros

  1. Good selectivity, sensitivity and S/N on FM
  2. Batteries lasted quite long (current draw: about 35 mA; specified at 20 mA for minimum output)

Cons

  1. The selectivity in the AM ranges isn't great (6.1 kHz / 17 kHz @ -6 / -60 dB), and there are lots of IM products (it's just a single conversion receiver).
  2. Only five SW ranges are available.

Reviews

  1. Test des ICF-7600W von Rainer Lichte (measurements are at the end of the text)

Servicing

ICF-7600 schematic – as one can see, this 1977 design is much different from later models, only sporting a total of two early ICs mainly providing FM and FM IF amplification and AGC. All the rest is entirely discrete, with 13 transistors, 1 FET and a bunch of diodes.
While having two ceramic FM IF filters and thus good FM selectivity for its day and class, for AM IF there is no more than a CFT class filter (1 ceramic element with two IFTs) plus another tuned IFT to be found, making it the equivalent of a 6-circuit receiver in classic radio nomenclature (middle of the road level basically and comparable to the later Grundig Yacht Boys or Philips D1835, but certainly quite good for its size back then).

Looking out for potential trouble spots, this is what caught my attention:

A few 7600 series receivers compared

Feature comparison

Radio ICF-7600D/DS (ICF-2002/2003) ICF-SW7600 ICF-SW7600G/GR
Min. tuning steps (SW) 5 kHz 5 kHz 1 kHz
Fine tuning AM yes yes no
Fine tuning SSB yes yes yes
Sideband selection in SSB mode no yes yes
Backlit LCD no yes yes
Stand on back no yes yes
Key protect no yes yes
German version: full coverage? no yes international version, so the problem is solved
Steps on LW 3 kHz 3 kHz 9kHz; 1 kHz
Steps on MW 9 kHz / 10 kHz 9 kHz / 10 kHz 9 kHz / 10 kHz; 1 kHz
Steps on SW 5 kHz 5 kHz 5 kHz; 1 kHz
Steps on FM 100 kHz 50 kHz 50 kHz

Shortwave gain stage / AGC overview

Gain distribution is an important topic in receivers, as it affects both obtainable sensitivity and dynamic range. If you have a noisy mixer without any preamplification and feed this with the modest signal levels of a telescopic antenna, the receiver won't be very sensitive. However, if you stuff a lot of gain into the RF preamp, the poor mixer may overload far too quickly. (Some noise figure calculations are helpful in striking the right balance. You need to know the antenna's noise figure, of course – a big antenna will always catch a lot more atmospheric noise than something as mismatched as a telescopic whip).
The bandwidth of the various stages also plays a role, as it not only affects sum signal levels but also decides on which signals can still generate unwanted intermodulation products in following stages. The signal handling capability of the mixers also plays in – normally the requirements are less strict down the line in spite of some gain, as bandwidth is strongly reduced, but this is not always the case, as the analog models (ICF-7600A/7601) show.
(Weaker 2nd mixers aren't possible either if high close-in blocking / dynamic range is required, something typical for ham radio field days where another OM only a short distance away might be operating close to the desired reception frequency. For these applications, an equally good or even better 2nd mixer may be warranted, and/or a narrow – read <1 kHz – roofing filter on the 1st IF for narrowband modes, e.g. CW.)

Proper gain distribution in battery operated receivers is not at all easy, as not only signal levels (on the whip in particular) may differ quite a bit between battery and mains operation, but also dropping battery voltage may lead to reduced gain. Few receivers offer the flexibility needed to cope with such strongly varying input levels.

Where AGC (either as variable attenuation or direct gain control of an amplification stage) is applied affects both quieting characteristics and strong-signal handling. In the kind of receivers we're looking at here, there is only one AGC loop whose control signal is derived from demodulator output or pre-detector 2nd IF level. Now consider two scenarios:

  1. Rx tuned to empty channel on an otherwise busy band
  2. Rx tuned to strong station on a busy band

While it is clear that frontend gain should not drop too early (which would reduce SNR and thus lead to less steep quieting), no AGC in front of the first mixer in particular may mean that reception of stronger stations is still disturbed by intermodulation products, forcing the user to activate the attenuator. In the first scenario, only gain distribution and mixer signal handling capability will determine rx behavior.

The following table illustrating gain and AGC aspects of the various 7600s was split for space reasons. The first part covers the various "digital" models.

Model SW7600GR SW7600G SW7600 7600D/DS
RF stage
Bandwidth X-Wide
Hi/Lo-Pass
X-Wide
Hi/Lo-Pass
X-Wide
Hi/Lo-Pass
X-Wide
Hi/Lo-Pass
Gain Medium
Source fol.
Medium
Source fol.
Medium
Source fol.
High
Com. src.
AGC Post-Amp Post-Amp None Pre-Amp +
Var Gain
Attenuator Variable
Pre-Amp
Binary
Pre-Amp
Binary
Pre-Amp
Binary
Pre-Amp
1st mixer
Type Dbl. bal. FET Dbl. bal. FET Dbl. bal. FET Dbl. bal. FET
1st IF
Bandwidth Narrow
Xtal filter
Narrow
Xtal filter
Narrow
Xtal filter
Narrow
Xtal filter
Gain stage Yes
Post xtal fltr
Yes
Post xtal fltr
Yes
Post xtal fltr
No
(post 2nd IF fltr)
AGC No No Yes
Pre-Amp
No

All of these use double balanced mixers, and for good reason – when using a wideband frontend, their 2nd order intermod rejection and generally better strong signal handling when compared to unbalanced mixers are really needed.

The second part covers analogs and unique models. These all use band filters and therefore have to make do with unbalanced first mixers.

Model 7601 7600DA 7600A
RF stage
Bandwidth Med
Bandpass
Med
Bandpass
Med
Bandpass
Gain High
Com. src.
High
Com. src.
High
Com. src.
AGC Pre-Amp Pre-Amp +
Post-Amp
Var Gain
Attenuator None None None
1st mixer
Type Unbal. FET Unbal. FET Unbal. FET
1st IF
Bandwidth Wide
Cer. filters
Narrow
Xtal filter
Med/Wide
Cer. filter
Gain stage No No No
AGC None None None

The analogs have a somewhat critical combination of high RF plus 1st mixer gain with a wideband 1st IF and less well-performing second mixer. (As explained in the '7601 section, the wideband 1st IF was deliberately chosen to improve frequency readout accuracy and stability.) Only the '7600DA uses a narrow crystal filter but still has high RF gain.

Utilities

The AN-LP1 antenna

In January of 2004, I finally obtained a (used) AN-LP1 antenna, a project that had once been terminated after the decision to get an AR7030. Now the AOR isn't exactly a portable, so... My AN-LP1 (JFTR: S/N 15243) had been modified quite strongly by the previous owner who, among other things, removed the cloth (for better handling, I suppose), wrapping something around the wire and frame - well, a "naked" AN-LP1 doesn't look exactly pretty, but reception is unaltered. So, what about a little review?

Handling: I got the folding twist right virtually on the first try (after use, the antenna has to be folded together again, which had been reported as being a bit tricky until you get the hang of it), though it's quite possible that it would be more difficult with a stock antenna frame. Operation is quite simple: Unfold antenna module and attach it somewhere (that's a bit of an unsolved problem on this antenna, you can clip it somewhere and attach it to windows and such, but that's about it), connect antenna controller to both antenna and receiver (if you were wondering what the somewhat strange-looking longish part is, that's a filter into which you plug in the cable from the antenna controller on one end and connect the thing to the antenna frame with the other end), put in two AA batteries into the antenna controller (I used rechargeables, since I didn't have anything else at hand, and these work pretty well, with the switchoff voltage being roughly 2.3 V) if not already present, and off you go. At least if you have a receiver with a "hot" EXT ANT socket, like the ICF-SW7600G(R), ICF-SW100 or ICF-SW1000T. On others, it's necessary to explicitly turn the antenna controller on with the respective slider switch. While receiving, it's necessary to select the correct frequency range for best reception.

Reception: That's what we bought this thing for, right? And so far, the AN-LP1 has not disappointed me. One must know, of course, that it's only good for the frequency range from about 80 meters to 13 meters, with a preference for the lower frequencies. There the antenna really shines, with signals that are a lot stronger – say, 20 dB – than just with the whip (even when using an antenna tuner, [ADDX-PRE-1]), and usually cleaner than the signals of a tuned whip + AN-71 combo. Also, the preselection helps a lot to minimise IM (like on 80 and 22 meters, where at the time of testing the wire overloaded the receiver on the respective frequencies), and with the apparently rather sharp 5 MHz range, images from 49m on 60m (a nuisance of the 7600G) are considerably attenuated. (19m images on 20m are strong as ever, but you can't have everything.) Minimising interference by rotating the loop is also nice. Performance, while still good on 16m, is no longer stellar on 13m, where the difference to the whip + tuner is no longer that huge.

All in all: Recommended. If you need better reception "on the go", the AN-LP1 makes a good travel companion. (And not only that – it'll also deliver good performance at home and with the receiver used on a wall wart. I've retired the AN-71 for now.) Unfortunately, its availability has never been too great (apparently it's only being made once in a while, in small batches), and the price may also seem a bit deterring, given it costs about half as much as an ICF-SW7600G(R) when new.

Misc. headphones

Oh boy, I certainly have come a long way in terms of headphones since I wrote the paragraph below. Today I'd prefer 600 ohm retro cans with slightly forward upper mids, like my trusty Sennheiser HD420SLs. Those may not be a good choice for radios that are overly rolled off in the highs (e.g. ICF-SW30, DT231s are a better match here), but they do well on my array of '7600' models, and there are no problems with amp hiss, frequency response warping due to output impedance or bass rolloff due to smallish coupling capacitors to be feared.

Since the sound via the speaker isn't too great (*grmbl*), I mostly use my 7600G with phones. At home, that's the Sennheiser HD 590 (very good sound IMHO, though the comparatively high impedance isn't ideal for this radio since you easily get amp hiss), while "on the go" I used to have a Koss KSC50 and am currently using a Beyerdynamic DT231 (with foam modded earcups), albeit not with the trusty 7600G but a (more compact and economic) Panasonic RF-B11.
Generally (when listening to FM and other stuff via my home hi-fi setup) I find the HD 590 to give the best sound of those three (not surprisingly), followed by the DT231 and then the KSC50. The Koss part should have been better (it uses the same drivers as the PortaPro after all), but it seems I'm not the only one who couldn't persuade them to fit tightly against the ear without becoming uncomfortable. (The older KSC35 and current KSC75 apparently fit noticeably better. These are generally considered excellent budget choices.) My main complaints were that percussion would sound "paperish" at times (the fit issue certainly didn't help here), and then storing them quickly and safely at the same time wasn't an easy task. The DT231 may not be all too comfy if you've got big ears, but provided it fits it's quite acceptable in the comfort department (and you don't get sweaty ears due to the velour earpads) and provides some (though not outstanding) isolation from outside noises. It's not foldable or anything, but reasonably small nonetheless. (For something foldable, the Sennheiser PX100 or a PortaPro may be an option to be considered. Both of these are totally open, however.) Lately I happened to plug the DT231 into a relatively newly acquired ICF-SW30 and was pleasantly surprised about the sound on the short waves, which turned out to be very smooth. The reason for this probably is the dip in the frequency response (about 6..7 dB down) which extends from a bit above 2 kHz to about 4.5 kHz. Not too bad a characteristic in this case, as it gets rid of a good part of the distortion typically associated with AM diode demodulation without muffling things all too much.
For more headphone suggestions, I'd suggest turning to Head-Fi. Frequency response measurements for various headphones can be found on Headroom

Next: Modifications

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Created 1999-06-01 (yyyy-mm-dd)
Last revision 2009-12-04