Sony CF-550 available from 1971 to 1976. This particular model is No. 14273 according to the back label. The gimmick here is the "Four Speaker Matrix Stereo Sound". This was something else I wanted to hear for myself. And another reason to try this old Sony. (Below is the Service Manual explanation. There is a schematic of the circuit also but I have not included that here.) Purchased from e-bay on September 16 2022 for $124.95. Included cardboard box, two Styrofoam blocks, power cord and old NiCd battery pack. No manual. Seller got it from an estate sale in the Spokane Washington area not long before. Said the Estate sale seller was "quite proud of it" and was son of original owner. (Why didn't he keep it then? All it needed was a shot of Deoxit on the pots and usual "Record Bar switch". Kinda sad as it was his Dad's and should have been kept around. But that's just me I guess) Everything worked fine. But weak audio on right speakers sometimes (from perspective of listener facing the radio head on). Classic oxidation case. Not in balance or volume but the usual Record / Play bar switch. In this case it is a large 20 pin two-position slide switch on the main board that is actuated by metal rod arm. From the service manual components list I ordered all replacement electrolytic capacitors in Nichicon FG and a couple of Nichicon KA (blue) where values unavailable. Instead of removing the entire board and having to de-solder the bundles of wires... I did something a little off the wall and nutty: Replaced each capacitor one at a time in situ. Very careful prep and cleaning of every solder landing and trace after old cap removal. Around 47 caps including radio and its FM MPX decoder board. So old it has a separate MPX decoder portion for the FM. Build Quality: As others have said, regarding this CF-550 and its bigger brother from 1976 the CF-580, it is very well constructed. Lots of 3.5mm thick metal framing and support for speakers, main board and cassette mechanism. Unit is unusually and deceptively heavy. Just what I like Speaking of the cassette mechanism... there must be quite a few fans in Asia... there is even a little dedicated video on youtube to it. CF-550 is known as CF-2550 in Asia. EDIT: Well that didn't last long. Video was taken down already. Maybe they want to keep it a secret so they can buy em' up cheap for parts Just because it has an old all metal tape mechanism does not mean it sounds great. The first belt I tried was sounding worse than the 51 year old original. Had to take apart again and replace with another belt that was for the CF-160S, same cross section and just 10 or 15mm smaller in length. Fit fine. Sounded way better. From the Portugal e-bay seller and made in Germany VS the one made in UK. EDIT: --> The DeckTech replacement belt being sold on e-bay from the UK is ok. I had discarded it and used a slightly stretched CF-160 belt after disappointing initial results. That was my own error in not adjusting the tension screw on the flywheel correctly. As of February 2024 I have settled on the DeckTech belt for now. Frequency in WFGUI is now back to the 2980 range with slightly improved W&F over the CF-160 belt. BUT adjusting the tension on the flywheel alleviated a lot of W&F. So it may have been more of that being the issue the first time around, not the belt, but in fact my error. Tricky deck to work on. Took many hours to even reach the belt the first time, agonizingly slow process, with service manual pages printed out and refereed to constantly. Second time around took about 25 minutes. Large heavy flywheel's capstan oiled with synthetic oil. White plastic tension screw ascertained with a feeler gauge of thin plastic card. Relaxed screw and observed behavior again and again. Here are the WFGUI results with a 3khz test tape. (Somewhere there must be a pot to adjust the motor speed and get the frequency closer to 3khz? I could not find one but I did not go too deep into the schematics.) 2946.4 0.1712 0.3343 2945.7 0.1829 0.3899 2944.9 0.1775 0.3899 2945.3 0.2108 0.3939 2949.1 0.1613 0.3939 2944.4 0.1669 0.3939 2944.1 0.1634 0.3939 2946.9 0.1861 0.3939 2948.3 0.2158 0.4092 2949.5 0.1483 0.4092 2948.4 0.1665 0.4092 2946.0 0.1932 0.4187 2947.9 0.2029 0.4252 2949.7 0.1785 0.4252 2945.5 0.1569 0.4252 2948.1 0.1738 0.4252 2948.3 0.1423 0.4252 2946.5 0.1504 0.4252 2949.9 0.1353 0.4252 2951.2 0.1664 0.4252 2951.2 0.1343 0.4252 2950.3 0.1631 0.4252 2948.3 0.1319 0.3531 2948.9 0.1438 0.3337 2946.1 0.1163 0.3337 2948.5 0.1389 0.3337 2947.1 0.1748 0.3337 2948.2 0.2765 0.5257 2946.4 0.2342 0.5257 2948.9 0.2285 0.5257 2948.0 0.1858 0.5257 Sound quality: It's quite good, but compared to what? That's the problem, I don't have a mass of boxes to compare it too. But the bass is limited as expected. There is the usual Tone control and Balance. That's it. Two forward facing 3x4 speakers and Two side firing 2x3 speakers. FM radio sounds "really good" up close. There is a 3D stereo kind of thing going on with certain music at times. I dunno. I just can't evaluate it without a ton of other big boxes to compare it to. Basically, if I had to sum it up, low bass, would be the overall comment. But that is typical of these small boxes of the period. EDIT --> As of early 2024 after more work I would now say the sound quality of the cassette playback in CF-550, from my own recorded Type I normal tapes (NOS e-bay TDK and Sony from late 1990's.) made on a well tuned D6C (from PC optical out playing .WAV files, going into Headroom Ultra DAC then to D6C with short Cardas cables) are really quite something in even basic headphones like Koss Sporta Pro. Far better than I had expected or thought possible or likely. Low background noise. Wide soundstage and transparent. I don't want to hype it too much. Keeping the tape head absolutely clean of oxide makes a noticeable difference in this regard. Such a big difference to volume and clarity after cleaning. Also, maybe the 100% capacitor change helped a lot more than I had hoped? I mean that was the purpose of doing it, those 51 year old caps were inferior audio caps even when they were freshly installed at the factory, right? After the Transistor change it sounded a bit louder on speaker too. Just this past weekend started using headphones again and was surprised at what I was hearing. This box is never being sold. Forget it. (But it also makes buying another old boombox seem pointless. Why bother? I got lucky the first time. Quit while I am ahead.) FM radio reception is impressing me a lot. Very sensitive. The FM dial is packed with stations. And the stereo separation and 3D effect is unlike anything I have heard on other boomboxes such as the Hitachi 3D5. With the CF-550 sat on a solid wood table about 3 feet high (90cm) and 2 feet (60cm) in front of the listener the effect is nutty on some Rock 101 classics. Even with my cassette recordings it sounds nearly as good in playback too. The local Co op radio station 100.5 even had some kind of space drone type music going on for half an hour non stop. Renewed my faith in humanity and the FM dial! I did not have / could not find the pictures of Radio board and MPX board with all caps replaced! Capacitors are half replaced in this shot. Now they are all replaced. Leaf Switch needed cleaning as usual. Black with oxidation. Series of quality control check off marks and serial label?
Hi - can you explain how you got access to the cassette deck to replace the belt? I've tried by undoing the PC board above it, but that doesn't seem to move enough to give me access. Many thanks, John
As I said above: "...Tricky deck to work on. Took many hours to even reach the belt the first time, agonizingly slow process, with service manual pages printed out and refereed to constantly. Second time around took about 25 minutes...." Make sure to get the service manual .pdf file for free. I think I got it here: https://elektrotanya.com/sony_cf-550.pdf/download.html Make sure to send for the proper belt. Not some random cheap assortment package. A good belt specifically for CF-550 is about $8 on ebay from the UK. Print out the pages of the service manual that deal with taking it apart. To get access to the cassette area. Lots of screws. Remove the single Philips screw in the cassette. Remove the cassette door and take out the single screw in there. Then Radio portion has to come out, then cassette board, both placed to the side with all wires attached. Then the big heavy metal internal chassis part with cassette can lift out and be put to the side. It's not easy or fun to replace that belt. Are you sure you need to... is the W&F really bad? While deck is apart you need to Q-tip wipe rubber surfaces of the idler tires with about 70% alcohol. And when flywheel is removed the capstan rod should be cleaned and oiled. Watch out for small oil seal washers falling off the capstan etc.,
Hi - many thanks. Have the service manual, and have the relevant radio/cassette sections out of the case, but still can't see how to access the belt. It definitely needs replacing as is/was lying in pieces on the bottom of the cabinet. I have the correct belt ready to go.
I don't have the full image collection here on this computer to show. Will try to get extra pics up for you Monday. Basically, you have to take off a chunk of the deck, with 2 or maybe 3 screws (can't recall offhand), in order to gain access to the flywheel bracket. Just observe what is in the way of accessing the flywheel. Need to loosen and gently pull away that portion, just enough, then replace after.
Thank you! I finally did it. Easy'ish when you know how. Although I assume Sony thought the belt would never need replacing. Thanks again!
OK great. When I first replaced this belt I did not get the tension / pressure correct on that bracket pushing down on the flywheel. Too much pressure. So the Wow and Flutter was horrible. Measure clearance with a feeler gauge (business card or thin plastic card) first before removal of bracket. Also mark edge of bracket with a marker to position it back level and not lopsided. (Proper method, as usual, is to just measure the current draw of motor and follow service manual steps on adjusting the white nylon screw. I wanted to leave the set screw sealed in the original locking paint.)
Thanks, I just scribed around the bracket and put it back as close as possible to where it was. All seems OK. Although now another problem to fix, no sound from tape on left channel. Radio is fine on both channels.
Dead on left channel or intermittent? I had intermittent audio on left channel on tape also. As time passed it manifested on radio also. I could smack the radio on the left side a few times and it would change - sometimes lots of crackling - sometimes audio coming back loud and strong - other times only partially. Sometimes muffled and very low volume. I had already changed every single electrolytic capacitor... so a massive de-oxit campaign began where I treated every pot and switch, including the inside radio / tape mode switches that the levers control. Sounded better when it worked... the de-oxit lowered the resistance of the switch contacts and volume-tone-balance pot traces... but no solution. Checked every wire connection and solder point too. Knew it was an amplification stage issue and most likely a transistor. Sure enough, issue is in the 2SC633A transistor, same issue plagues other Sony products from the 70's, Google turned up other forums discussing this and what replacement to buy. The replacement to get is KSC1815YTA and they are very low cost. What threw me for a while was the curios intermittent nature of the issue - and the fact that a good old whack to the side of the radio caused massive crackle, pops, often restoring full strong audio! So here is what I did: With the CF550 opened up I installed the 4D batteries and turned it on. Audio playing only on left side. Then I went around the main cassette and amplification board manipulating wires, connections, tapping the transformers etc,, When I got to one of the 2SC633A transistors, located tight beside one of the transformers, tapping it the audio went crazy. That was the problem. So I bent the transistor over to one side. And that has solved the problem for the last few months. Temporarily. Because I know I have to just bite the bullet and replace every dang 2SC633A to really cure this CF-550. On the back of the circuit board, under one of those rotted brown foam pads, the location of the transistor even has "L side" or words to that effect. I can get a picture up for ya if you want to try doing what I did.
HI - thank so much for all that detail. In my case it's dead (well, no audio, but with volume on full - audible hiss). All OK on radio though. If you have it a picture would be appreciated! Maybe I should also buy some replacement transistors.
It was one of these two, Q203 or Q303, that in my specific case, was the source of the left channel audio problem. They are both 2SC633A transistors. Google "2SC633A sony" and spend time reading about the adventures other people have had with these old transistors. As well as the arguments over what is a suitable replacement. This board also has a few 2SC631A transistors. It was stated in those discussions elsewhere that the same modern replacement, KSC1815YTA, was suitable to replace both 2SC631A and 2SC633A since they are so similar. If you don't want to do the replacement yourself, I would suggest: Order the parts, get them, print the service manual in full, plus put the .pdf on a new thumb drive, then try calling audio / electronic repairs shops in your area and see if they can do the job for you. Of course, this assumes the "no audio on the left channel" is being caused by these transistors and not one of the other actual amp transistors or other possibilities. YMMV. In my case it was these components at fault. But other CF-550's may have a bunch of other issues that cause the same left channel symptom. NOTE: Board layout images (from backside) differ from my photo by being upside-down and reversed.
Hi - many thanks for yet more detail and pictures! Appreciate it. I can do the replacement of transistors myself, so will get some and see if replacing them helps. I'll start with the ones you identify, and go from there. Thanks again!
Extraordinary engineering & build quality! Look at that cassette mechanism......back when you had brakes for the take up & often the supply reel! SO many wires but unpluggable in many many places......Mind boggling how far downhill it all went in the 80's & beyond!
Yes. The #1 reason I wanted to get one of these early Sony's was to experience the awesomeness of the build quality. The bundles of wires were even hand tied up with fine white thread in a few places. So much manual hand work. The metal is so crazy thick and solid. Whole cassette mechanism is laughably heavy with literally not a single bit of plastic apart from the gears. No wonder this thing cost $200 US in 1971. There was a video on youtube where someone had the cassette mechanism removed and they put it on a 360 rotating display stand and let the video roll. Then turned it over and let the viewer see. I posted a link to this video and then, shortly after, the video was taken down. Oh... but I downloaded the video! Good old "easy youtube video downloader". I use it all the time to grab vids that are interesting. The next one I may try to get one day is the Sony CF-580.
Finally sent for 20 of the KSC1815YTA Transistors a few weeks ago. First group I replaced were Q202, Q302, Q203 and Q303. That solved the intense crackle that would respond / modulate according to smacking the side of the radio - Transistor Q302, if I can remember correctly, was the culprit, the one with the different trapezoidal body style shape. But the intermittent fading and eventual disappearing of the Left channel remained. This past Saturday December 16 went in there are replaced the 13 other Transistors that the new KSC1815YTA could replace. As always, it is really necessary to take more detailed pictures of the board and traces with solder joints, for before and after inspection to make sure a solder bridge has not accidentally formed with a neighbouring landing / pad. And pictures of the component side to confirm orientation of parts. Several (about 3 I recall) of the Transistors had their lead "legs" routed this way and that - crossing over themselves which was deceiving and tricky - so make sure to study each one prior to removal, it's orientation, Emitter Base Collector leg routes and true destination / origins etc., I had to check the service manual schematic once to make sure the Base and Collector were not reversed on either Q302 or Q202, I can't remember which one it was now, but they had the leads twisted around to reach the destination. Anyway, as expected, once the others were replaced that solved the Left channel problem. Which Transistor was the one, I don't know and don't care, just replace them all. Audio is a little louder than before. And the Balance pot is not as "balanced" as original. Not that is was originally anyway. But otherwise the sound seems clearer to my ear. Improved. Once again I find myself impressed by the cassette playback "low noise" levels compared to recollections of early tape experiences. Those old junk recorders I had as a kid were filled with tape hiss on playback. This CF-550 seems free of that to a large degree - that I thought was not really possible. Remarkable clarity for such an old boombox. Then again... I did replace every single electrolytic capacitor with Nichicon Fine Gold audio caps so that must have improved things. So after 14 months I have all of the issues resolved. It now stands at 100% functional. Was it worth the effort? Yes. The only issue was a few bad Transistors... and the usual cassette rubber stuff... It did not even really badly suffer from contact oxidation or bad switches.... It's a great looking compact "boombox" with extraordinary build quality. One of the few that I could "believe in" so to speak. Would I go through it all again? Will I buy another old box in future? Yes... there are only 2 other models that I wanna try out next year... Another Sony (somewhat rare and therefore shall remain unmentioned...) and the obligatory JVC RC 550. Old removed Transistors pose for their group photo. Image the board solder points for careful check for accidental solder bridges formed when removing old Transistors. I caught one such bridge thanks to such diligence. Densely packed component population. I used a locking Hemostat to grab and lock onto the Transistor to be removed. I still do not have a solder vacuum pump station so had to it manually - easy enough. When one has small dexterous hands.
The first time I have used the Canadian inflation calculator I'm not surprised. I have a Weltron 2001 which inflation adjusted cost around £1000 back in the day. There again nobody was spending £1000 on a computer or mobile phone. A former colleague who would have been 24 back in 1971 commented that once you had bought a TV and an audio system there wasn't really much else electronic wise left to buy. p.s. This is American (Sears) but shows that even a basic cassette recorder wasn't cheap back then
