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Old 10-03-2020, 01:13 PM   #1
momaka
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Talking Sony CFD-E55 boombox blown line transformer & repair

Is a mid-2000’s boombox worthless? - I’d say probably yes or at least certainly a candidate for this thread:
https://www.badcaps.net/forum/showth...post+worthless

Long story long , my dad picked up a Sony CFD-E55 boombox over a decade ago from the trash room in a condo where we used to live.
(Note: picture below is of the boombox after the repair.)


He then put it in a box when we moved places and it sat in the garage for a few years. Eventually, I tested the boombox and found that it worked on batteries, but not on AC. Digging in revealed the internal line-connected transformer had an open primary winding and no thermal fuse (wires melted on a few layers, thus not able to repair it in any way, and I had to crack-open the plastic shell on the transformer, as seen on the pictures below.)



So I made a power plug for it to fit a spare 15V, 4 Amp laptop power adapter I had at the time. I even posted the repair here in the ghetto mod thread some 8 years ago.
Old picture of the repair: https://www.badcaps.net/forum/attach...3&d=1353991011

While that repair did work OK, I noticed that the amp IC would get quite hot, along with the linear regulator IC for the CD and Cassette Deck (hot enough to cause burning sensation, so probably 50-60°C.) I don’t know what voltage the original transformer output, but given that the output filter cap was rated at 16V, the DC voltage couldn’t have been higher and was probably in the 9-12V range. Thus, I suspect the 15V power adapter was probably giving a little higher voltage than originally, and hence why the regulators and amp IC ran hot. Nothing overheated with the 15V adapter, though, and the boombox did work OK like that. Moreover, it’s not like anyone used it much at the time, so for the most part, it sat idle in the garage. I actually did use it a few times when I found some old cassette tapes and was curious what was recorded on them. On that note, this Sony CFD-E55 actually has a really good, clean-sounding tape deck. Radio and CD also work great.

Jump “a few” years forward… with Covid-19 and everyone at home (myself included, as the company I worked for lay off its temp staff), my parents took on a lot of house projects. So my dad remembered this boombox again and asked me if I had fixed it so he could use it in the garage while working. I said, sure and set it up for him. But in the back of my head, I remembered the repair I did and wanted to re-visit it and improve on it - what better to do on a rainy day?

Starting with the power adapter I used (15V, 4 Amps)… let’s be honest: a boombox like this doesn’t really need such a large power adapter. Perhaps if the amp IC was one of those dual BTL jobbies, that current rating would have made sense. But this wasn’t the case here. The amplifier IC in the CFD-E55 is a Sanyo LA4601, which is a single-ended stereo amplifier chip. Its datasheet suggests that it can drive up to 2x 7 Watts (with ugly 10% THD ) into 3-Ohm speakers with Vcc of 15V. But it also states that if Vcc is 9V or less, the IC can be used without heatsink, which is how it was in this boombox (this hints the original transformer was probably rated at 12V or less.) All in all, though, the LA4601 amp IC is really nothing to write home about. The internal speakers in the CFD-E55 boombox are rated 3.2 Ohms and 3 Watts max. Doing the math… a 12V supply used in single-ended amp application means 6V max for the positive or negative peaks. Of course, the speakers would never see that, because of the biasing and internal voltage drops in the amplifier. So, assuming 2 voltage drops @ 0.7V for each 6V “side”, this leaves us with 4.4V max peak (and even that is probably somewhat inflated, but not unreasonable.) With the 3.2-Ohm built-in speakers, the max possible power from 12V should then be P = ((V_rms)^2) / R = [(4.4^2) / 2] / 3.2 = 3.025 Watts RMS. (In reality, the power output would probably be even lower, but this is a decent “best possible” approximation.) Thus, it looked like a 12V power adapter should be plenty to drive the speakers.

I wasn’t sure which of my 12V adapters to use (I have many), but I had quite a few like this one:
https://www.badcaps.net/forum/attach...1&d=1601752102
It is switching type, rated for 1.66 Amps at 12V, with a grounded plug. I load-tested it up to 1.6 Amps continuous, which it output with barely any voltage drop. What worried me more was the ground connection, as sometimes this can introduce line hum noise (especially if the boombox is to input or output audio to another grounded audio device.) I don’t plan on driving an amplifier with this boombox, though, and there are no auxiliary audio inputs, so the grounded adapter shouldn’t be a problem. Being switching type, it probably would interfere with AM reception, though.

Next step was to make a plug for the adapter. About 30 minutes later, and I had this:


A block of wood, a piece of nail, and a paper clip is all it took to make this, along with some drilling and cutting, of course. You can also see an ugly piece of aluminum I bent into an L-shape (more on that later below.)

Checking that the plug fit in the case as intended…


Painted and added some stickers (from recycled shipping labels ) for the expected voltage and current input, in case the adapter was ever lost (which shouldn’t matter, as I have two or three more of these spare):


To be continued… (10k char. limit always gets me )
part 1 of 2 posted
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Old 10-03-2020, 01:20 PM   #2
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Talking Sony CFD-E55 boombox blown line transformer & repair

part 2 of 2

With the plug part done, time to re-visit the amplifier board (Sony P/N: 1-675-291-11) for some modifications I long had planned. But first, here it is in stock form, minus the old line transformer (T901) and old AC plug (J901).


Don’t mind the lifted/damaged traces on the AC plug - this was caused many years ago when I was beginning to learn to solder

In the above pictures, diodes D901 through D904 were used with the old line transformer in a full bridge rectifier configuration. C357 is the filter cap for that - a YEC 85°C gp cap, rated for 16V and 6800 uF. Meanwhile, diodes D908 and D909 are for AC detection. More precisely, this boombox uses a rather basic scheme for running between batteries and AC power. Originally, whenever the boombox was plugged into AC, the old AC plug had a switch in it, which would disconnect the main battery source (6 series D-cells) and run the boombox from the rectified AC from the line transformer. So diodes D908 and D909 were used for signaling the power-regulating circuitry to provide various voltages to the deck/CD electronics. With AC gone and AC plug disconnected, the AC plug allows power from the batteries to pass to the amp IC directly. The battery compartment also has several taps between the series-connected D-cells, so that the batteries can directly provide various lower voltages to the deck/CD electronics, bypassing the linear regulators.

Knowing that and still wanting to keep the battery option functional, I fed both the battery and adapter power through their own diodes. For the battery diode, I used one from the bridge rectifying diodes (D901-904). But for diode for the adapter, I wanted a slightly lower voltage drop, so I used 4813NH N-ch MOSFET connected in reverse (i.e. using the body diode of the MOSFET.) After all, the 4813NH MOSFET I used had a physically broken Gate pin. Instead of discarding it, I gave it a second life as a diode rectifier in my junk box. Don’t laugh - high forms of recycling sometimes require more radical thinking!

With this dual diode setup from each power source, even if power is lost from the adapter, the boombox can immediately continue to operate on batteries, if there are any installed (not that I ever plan to use this feature, but why not still keep it, right? ) The MOSFET diode dropped only about 0.6V under the highest load, so the amp IC was getting around 11.4V, which is even better, since lower voltage means less heat from the amp IC and linear regulator.

I also proceeded to add a few other modifications. This was the result of those and the abovementioned ones:




Obviously, the biggest (literally) mod was a heatsink for the amplifier IC. I found this piece of aluminum on the side of the road many years ago. It had a MOSFET attached to it (which I detached and used for many of my breadboard experiments.) Even though this heatsink was ugly, deformed, dirty, and scratched, I managed to clean it up and straighten it easily. The length and width were just a perfect fit for this boombox (and it crossed my mind that’s where this heatsink would go right when I found it.) I call it recycling karma … but calling it hardcore ghetto wouldn’t be inappropriate either.

Next, the big sheet metal piece: I added this, because the old line transformer had a metal bracket that would hold the PCB onto the boombox case (otherwise the PCB would be loose in there, making the headphone jack hard to use.) With the old line transformer gone, this seemed like a good solution (it wasn’t, but we will get there as to why.)

And finally, looking at the bottom side, I added jumper wires across resistors R144 and R244. Why? -Because these resistors are connected in series with the load on the headphone jack. This is a good idea to prevent damage to headphones (either due to amp volume turned too high or faulty/shorted amp IC.) However, it does add distortion to sound. Of course, I wasn’t concerned about that. Rather, the idea behind this mod is to allow small (and better) bookshelf speakers to be connected through the headphone jack with a 3.5 mm to speaker output cable. I actually tested this after doing the mod with a pair of Kenwood LS-N451 6-Ohm speakers, which I’ve had for many years and know they sound pretty decent. The difference between those and the built-in boombox speakers was very significant. They were louder and bass actually sounded like… well, bass. Imagine that! Not that the CFD-E55’s built-in speakers are bad, or anything. But there is no baffle in the boombox case and it’s not really a proper speaker box anyways. So of course they will sound worse. Also, thanks to the speaker output coupling caps in the boombox being 2200 uF (Lelon brand with what appears to be week 33 of 1999 date code), this sets the -3dB low-cut frequency to about 12 Hz with my 6-Ohm speakers. The current draw from the power adapter was significantly lower as well - about 0.4 Amps max before significant sound distortion. That’s half less than the consumption with the built-in boombox speakers (which makes sense, since the built-ins have approximately half the impedance.)

Anyways, here is why I put on that steel sheet bracket:

It basically allowed the amp board to get screwed onto the two plastic standoffs on the boombox case. However, the flimsy steel sheet that I used couldn’t really hold the PCB too well, so the headphone jack would sag into the case every time a 3.5 mm plug was used. Also, this original arrangement of the PCB being held to the bottom part of the boombox made it difficult to shove all the wires and ribbon cables in the boombox when closing it together, especially with the newly added amp IC heatsink.

So, a slight change was in order:

I decided not to use the steel sheet bracket, and instead used a long piece of rigid steel wire to clamp down the PCB right in the boombox. To prevent the PCB from turning, you can see a pink piece of foam installed behind one side of the PCB (note: there are no components in that area, so there is nothing that can make the foam catch on fire.) This allowed me to neatly connect and route all wires and ribbon cables, away from the heatsink… except for the battery power ribbon cable - that was a PITA to connect with the amp IC PCB already mounted. But once done, everything closed up nicely. After testing the boombox at high volume for about an hour, I could feel the amp IC heatsink was doing its job, because I could feel slight heat coming from the vents right above the amp IC heatsink. Yet, checking the amp IC heatsink temperature revealed it wasn’t running that hot - only around 45-50°C, which is quite acceptable. The more worrisome temperatures were on the linear regulator heatsink, running 55-60°C. Unfortunately, there is nothing I could do about that one, other than changing its heatsink as well… which would have been a PITA, so I left it as-is.

Doing some tests with jumper leads revealed the CFD-E55 did not use more than 0.85 Amps @ 12V with the built-in speakers and volume high enough for bad audio distortion. This indeed confirms the “best-case” scenario calculations for the max power output that I did above. Given these numbers, the amp IC probably wasn’t using more than ~10 Watts, which suggests the speakers weren’t seeing more than 3 Watts (assuming 5 Watts went to each channel, and assuming 60% best-possible efficiency, as this is a class AB amp.)

With that said, I do remember the 15V adapter did allow the volume to be set a little higher due to the higher voltage. But the difference is hardly worth it. In the end, boomboxes like these aren’t really meant for loud listening or a Hi-Fi experience. So going down to 12V didn’t seem to matter much, aside from lower dissipation from the IC, which I thought was more important

After that, I closed everything up and set it up for my dad to use. He listened to it for several days while working in the garage (with the door open) in the midst of the summer heat (~30C / 86F.) So far, so good - this Sony boombox has been running well.

I also snapped a few more pictures of the electronics inside this boombox, just for those who may be curious here.
https://www.badcaps.net/forum/attach...1&d=1601752686
https://www.badcaps.net/forum/attach...1&d=1601752686
Not much to see really. Just your average plastic-fantastic audio gear from the 90’s and 2000’s… but this one isn’t that bad and, at least for some garage tunes, is OK. Plus, that’s one item less for the local dump to incinerate and pollute the air.
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Old 10-04-2020, 02:18 AM   #3
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Default Re: Sony CFD-E55 boombox blown line transformer & repair

why not just feed it with the intended 9v and with the volume up, meter the current?
maybe stuff a small switching psu inside.

btw, stuff like that is more usefull than you think,
i add a line-in connector and use them as portable amplifiers for testing and putting on laptops and other stuff with shit tiny speakers.

Last edited by stj; 10-04-2020 at 02:20 AM..
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Old 10-04-2020, 08:51 PM   #4
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Default Re: Sony CFD-E55 boombox blown line transformer & repair

Quote:
Originally Posted by stj View Post
why not just feed it with the intended 9v and with the volume up, meter the current?
Well, I don't know if 9V was actually the intended voltage or not. Only the LA4601 datasheet suggested that the amp IC should be ran at 9V or less if there is no heatsink. But that doesn't necessarily mean that Sony designed this properly and had 9V or less going to the amp IC.

In fact, given that the original power transformer is line AC type, you can bet the voltage was higher than 9V. Most line transformers designed for 9V output at full load typically tend to output 12-15V when lightly loaded or unloaded (and sometimes even higher.)

So giving the boombox a well-regulated 12V supply is probably as good as it can get.

On that note, I did try giving it 9V with a different power adapter before. The 6V regulator on the amp board still ran extremely hot, as did the amp IC when it didn't have a heatsink. At least now the amp IC runs much cooler with the heatsink I added.

Regarding the current: when I metered the boombox with the 12V adapter, the maximum current it drew pretty much flat-lined (to about 0.85 Amps) past a certain point in the speaker volume level - about 3/4 of the way, IIRC... which coincides with where the speaker sound became distorted. Checking the voltage showed good 12V going to the boombox, so it wasn't the adapter's fault. The amp IC was simply running out of headroom on the supply voltage and starting to clip.

With 9V, the current draw would have been even lower, but the speakers would have started to distort at lower volume. So I didn't see a good reason to go with 9V (and I have only one 9V adapter, whereas I have like 4 or 5 of these specific 12V ones among my many other 12V adapters.)

Quote:
Originally Posted by stj View Post
maybe stuff a small switching psu inside.
Yeah, I thought about that, but after analysis, I came to the conclusion it would be more work than making the plug and using an external adapter.

Quote:
Originally Posted by stj View Post
btw, stuff like that is more usefull than you think,
i add a line-in connector and use them as portable amplifiers for testing and putting on laptops and other stuff with shit tiny speakers.
I thought about that too (adding a line-in connector.)

Question is, where?

If I add it directly going to the amplifier IC pins, then I wouldn't have any control over the volume (or I would need to implement a second form of volume controls specifically for the line input.)
The better solution would be to find the IC that controls the volume (it's digital control on this boombox with + and - buttons) and connect the external line input there. But then that leaves the question how to do that without affecting the radio, CD, or tape function (as I imagine these would be the only inputs going to whatever IC there is for the volume controls.)

So in short, that too seemed like more effort than I was wanting to put into it. If nothing else, I would also have had to remove the two main boards and maybe the panel board to figure it all out.

Thus, for the time being, I think I can live with no external line input. If bad comes to worse and I really need that, I could get one of those tape-to-3.5mm audio jack adapters.

I think converting the 3.5 mm headphone jack to output without any power limits was a lot more useful mod. Like I said, I tested this boombox with a pair of 6-Ohm bookshelf speakers, and they sounded great. With approx. ~1 Watt going into each speaker, I was able to get quite a bit of sound (and bass) out of them.

Also, I think I was right about the AM reception - it's all just buzzing AC noise on any station. Don't know if that's because there's no AM reception in the garage (quite possible) or because the SMPS adapter is interfering with it (probably more likely... though I must note there are hardly any AM stations in my area anyways, and that was when I checked many years ago.)

Last edited by momaka; 10-04-2020 at 08:56 PM..
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Old 10-05-2020, 05:56 AM   #5
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Default Re: Sony CFD-E55 boombox blown line transformer & repair

so i said 9v because that's the battery voltage.

i usually tap my line input to the volume pot because it usually sits between the source, ground and the amp.

i dont know about AM, here we just use it to track electrical noise
but try with batteries - if it works then your psu is killing it - highly likely frankly because even lamp dimmers can effct it.
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Old 10-05-2020, 06:01 AM   #6
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Default Re: Sony CFD-E55 boombox blown line transformer & repair

is it a 1.0 or a 1.1??
https://elektrotanya.com/showresult?...a=All&kat2=All
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Old 10-05-2020, 04:58 PM   #7
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Default Re: Sony CFD-E55 boombox blown line transformer & repair

These boomboxes are quite rare to find and valuable these days.

All the cassette players that are on sale right now and for the last years, use the same cheap cassette mechanism or even worse a knock off.

This channel has covered this extensively:
https://www.youtube.com/user/vwestlife

Found one of the videos:
https://www.youtube.com/watch?v=tp105udgOjs

And this one tested new boomboxes with cassette player and they sound horribly:
https://www.youtube.com/channel/UC5I...W9gZPVkvzM8_Cw

They are not even stereo now. This is terrible.

So, I would keep the Sony boombox as a valuable item. I really like the modifications you did to it. No need to add line in and sacrifice cassette or cd functionality though.

And also, nobody cares about AM :P
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Old 10-11-2020, 11:53 AM   #8
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Default Re: Sony CFD-E55 boombox blown line transformer & repair

Quote:
Originally Posted by stj View Post
No idea.

Nothing on the outside labels to tell me. Probably written on some PCB inside, but I couldn't tell from the brief lookover I gave it again.

I'm sure they are similar, though, so I downloaded the one for v1.0. Amp section seems to match, anyways. Only difference I noticed was in the radio schematic, where you can see mine is missing IC3 and IC4, whereas on the v1.0 schematic, they are present. But I don't think that concerns me much.

From what I can tell from the schematic, I can try adding a Line In to pins 16 (R Rad. - i.e. right ch. radio) and 22 (L Rad. - i.e. left ch. radio) on IC301 (TA2068N.) There are basically two 10 KOhm resistors that connect to those pins - R107 and R207. Most likely I can add the DPDT switch before those to feed the Line In there.

I probably won't do it, though... but in case I change my mind, I think I've done my homework here, so I can just refer to this post and go from there.

Quote:
Originally Posted by stj View Post
i usually tap my line input to the volume pot because it usually sits between the source, ground and the amp.
That would have been very convenient.
However, this boombox uses an IC for the volume, which is digitally controlled through IC302 (bh3854as)... at least based on the v1.0 schematic above. I'll have to double-check this if I ever open the boombox again someday.

Quote:
Originally Posted by goodpsusearch View Post
These boomboxes are quite rare to find and valuable these days.

All the cassette players that are on sale right now and for the last years, use the same cheap cassette mechanism or even worse a knock off.

This channel has covered this extensively:
https://www.youtube.com/user/vwestlife

Found one of the videos:
https://www.youtube.com/watch?v=tp105udgOjs

And this one tested new boomboxes with cassette player and they sound horribly:
https://www.youtube.com/channel/UC5I...W9gZPVkvzM8_Cw

They are not even stereo now. This is terrible.
Wow, I didn't expect that at all.

People gave 80's and 90's audio gear (especially the 90's "plastic-fantastic" stuff) a lot of crap for being cheaply made... and indeed a lot of it was when compared to the late 70's gear, which many consider as the peak of Hi-Fi.

But as the saying goes, "things can always get worse" ... and looks like they have, at least when it comes to cassette decks.

Thanks for suggesting those channels, by the way. Great content there.

Quote:
Originally Posted by goodpsusearch View Post
No need to add line in and sacrifice cassette or cd functionality though.
Well, I looked into the service manual for this boombox that stj pointed to above, and I don't actually need to sacrifice anything, more or less. Basically, all I would need is a DPDT switch and wire the line input on the input of the mixer amp IC (so this way, I can toggle between Radio and Line In.) But in all honesty, this is probably a function I just don't think I will ever need to use with this boombox, so I'll skip it for the time being. If needed, I can add it in the future.

Quote:
Originally Posted by goodpsusearch View Post
And also, nobody cares about AM :P
Actually, a lot of Hispanic workers here do (particularly on construction sites and similar), because there are a lot of Hispanic AM stations still.

But yeah, I personally don't care much about any specific AM station, so the "loss" of that function is not that big of a deal to me.

Last edited by momaka; 10-11-2020 at 11:57 AM..
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Old 10-11-2020, 11:59 AM   #9
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Default Re: Sony CFD-E55 boombox blown line transformer & repair

In regards to the AM radio reception, though...

Quote:
Originally Posted by stj View Post
i dont know about AM, here we just use it to track electrical noise
but try with batteries - if it works then your psu is killing it - highly likely frankly because even lamp dimmers can effct it.
Yup, I was curious myself to see how that will turn out, so I tried it today.
(And I was also curious to see if my modification for the power switching between batteries and SMPS would work - i.e. if the boombox can continue to operate on batteries if I unplug the SMPS... and it did without issues. The original design didn't allow for this, so YAY!)

SMPS is indeed killing or greatly reducing / mucking up AM radio reception... though I should also note that where I was initially testing in the garage in post #1 above, I can indeed confirm that AM reception there is very very weak. Once I moved to the top floor in our house, I picked up 4 AM stations total on auto-tune with the SMPS adapter and 5 or 6 stations total on batteries. 4 of the stations that I picked up while using the SMPS were part of the 5-6 station I picked up on batteries. The difference, however, was that on batteries the noise on the stations was a lot lower.

So then I tried another experiment: tunning manually and going through each AM frequency. While connected to the SMPS adapter, a good deal of the stations buzzed very loudly. Yet, when I tried this same experiment on batteries only (SMPS unplugged from wall), I was able to catch a station (a lot of them were very weak, but still audible) almost every 2 or 3 frequencies apart.

Just for fun, I attached three mp3 sound samples (see Zip archive.)

- 1st sound sample is of an AM station with fairly strong reception (though the auto-tune didn't stop over it, for some reason.) Here, you can hear the AM station while the boombox is running on batteries. A few seconds into the sound, and you can hear the noise floor shoot up quite a bit when I plug in the SMPS adapter and the boombox uses that over the batteries. Then I unplug the adapter again after a few seconds, and you can hear noise go away again.

- 2nd sound sample was recorded in the same manner as the 1st one above: AM reception on batteries, then plug in SMPS adapter (hard to miss it! ), then unplug SMPS from the wall again. The only difference is that this time around, the AM station I tuned to was quite weak to begin with. So with a weak AM radio station, the SMPS can completely drown out the reception.

- 3rd sound sample is of the same weak AM station as the 2nd sample above. But here, I unplug the SMPS from the wall and from the boombox. After recording the AM reception on batteries in the first few seconds, I then plug in the SMPS into the wall but NOT into the boombox. You can still hear a lot of noise that gets picked up from the SMPS, but at least it doesn't completely drown out the reception.

So yeah... SMPS + AM radio don't mix well.

I pretty much expected that, of course.

Last edited by momaka; 10-11-2020 at 12:15 PM..
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Old 10-25-2020, 07:04 PM   #10
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Default Re: Sony CFD-E55 boombox blown line transformer & repair

thanks for doing that, I have an old vintage 70s or older AM radio that runs on batteries only that I would power it on when I was a kid and had great AM reception.

Meanwhile, on 1996 I got my first hi-fi, a Philips FW330 that I really loved and used daily for cassete and cd that had both FM and AM and the classic AM antenna. The interesting part is that it reaaally sucked in AM reception and sound quality compared to the vintage 1 speaker (mono) AM radio. I guess, the latter one getting powered from batteries only and the hifi from mains has to do with this.
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Old 10-26-2020, 09:06 PM   #11
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Default Re: Sony CFD-E55 boombox blown line transformer & repair

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Originally Posted by goodpsusearch View Post
Meanwhile, on 1996 I got my first hi-fi, a Philips FW330 that I really loved and used daily for cassete and cd that had both FM and AM and the classic AM antenna. The interesting part is that it reaaally sucked in AM reception and sound quality compared to the vintage 1 speaker (mono) AM radio. I guess, the latter one getting powered from batteries only and the hifi from mains has to do with this.
Nice.

Well, I certainly wouldn't blame that Phillips FW330. In the 90's and even in the early 2000's, these type of home audio systems almost always used line type transformers and not SMPS. So the poor AM reception might have been caused from an external source. Chances are, if you had a PC with an ATX PSU back then, that was very likely the cause of the noise, as early ATX PSUs often lacked input EMI/RFI - at least all of the small brands (and most PSUs were small brands, save for Delta, Astec, and a few others that actually did build their PSUs properly.) So I'd say that was the most likely cause. With my experiment, as you saw, I didn't even have to have the boombox plugged into the SMPS adapter. With just the adapter plugged in the wall and near the boombox, it already wiped out a good deal of the AM reception. Perhaps I should have taken the boombox and see how far away the SMPS adapter would still disturb the AM waves. But then, I don't know if I could even do that anyways. Almost every room in the house has some kind of device that has either a built-in SMPS or external SMPS adapter. So it would be hard to know exactly what's knocking out the AM.
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