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Sony Walkman FX-290W Right Channel Dead

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Hello, AudioKarma friends.

My boyfriend has recently gotten into cassettes (hipster) and purchased a Sony FX-290W Walkman for just under 10 dollars. The seller claimed that the right channel was dead but the device was otherwise in good shape and you can just unplug the headphones slightly and hear through both headphones.. I gave him the go-ahead to buy it thinking it would be an easy fix. I thought it was probably just a bum solder joint somewhere or maybe the headphone jack was dirty or something stupid like that. We get the device and I pop a tape in and sure enough the right channel is dead. I took it apart and didn't see anything glaringly obvious, but still reflowed all the headphone joints and all the ribbon connector joints from the tape head. Pop the tape back in and NO change. Bummer.

Then I tried the radio.. and the radio works through both head phones..

Uh oh. This may be tougher than I thought.

Since there are only a few electrolytics on the board, I figured I would test those next. Maybe a coupling capacitor or something.. but all the electrolytics seem to test fine in my little tester. Capacitance is pretty close to what's expected and low ESR across the board. (I circled the ones I tested).

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I then went and reflowed just about every joint I could find on this side of the board, but still no fix.

And of course during this process I managed to tear the ribbon connector so then I had to solder some wires to fix that. It's back to it's former state but I'm nearing the end of my ideas. ChatGPT keeps recommending garbage and I haven't found a lot of videos dealing with walkman repair except for replacing the belt.. I know how to replace the belt -_-. I'm just wondering if you all have any suggestions or if I should just give up on this and call it a loss. The worst part is my boyfriend is fine with just keeping the headphones half plugged in. It would drive me absolutely INSANE to have to do that but alas..
 
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Also I'm not sure why AK wouldn't let me post more pictures but here are a couple more.

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Also I noticed some oxidation here on this IC301. Could that be the issue? How would I even go about fixing that?

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I'd try putting it in play mode and then touching the pins on the tape head with a probe and see if you get any noise in each channel. That will let you know if the problem is the head or something else.

Regarding the IC, you can do a web search on the part number and see if it's meant for tape use or it's involved in the entire unit.
 
Thank you for the suggestion! I don't think it's a problem with the tape head as I checked it with my multimeter and I'm getting ~200 Ohms on both sides of the head. And I also don't believe the tape head is misaligned (visually speaking).

I wasn't able to find much regarding the IC's part number but while I was referencing older Walkman service manuals I found that IC301 is always right after the tape head which leads me to believe it's the preamp or maybe preamp+amp. I did just find something REALLY weird though! I reflowed a few more bits and tried to play a tape and when I engaged the Mega-Bass I noticed I could hear audio in the right ear! But it sounded like it was ONLY the additional Bass from the Mega-Bass. Like I could hear the normal audio + the Mega-Bass extension in the left ear but in the right ear I could hear only the Mega-Bass extension. How strange!
 
I found this article for a different model Walkman which mentions that this IC (assuming it's the same. but it seems likely) is a playback preamp chip. There's a reference to a chip number (MHC8570EQ01L) but from there the trail went cold. It does seem as if that chip was used in a few different models. If you can find the data sheet, you can test the outputs. You mentioned oxidation; is it actually on the legs? If so, cleaning and resoldering might be in order (although as an SOIC, that might not be easy)
 
So I found a service manual for an older walkman that looks very similar to the one I am working on here. I'm trying to not be discouraged but from what I tell.. for what I'm experiencing to happen there almost certainly must be a problem within the IC301. The audio path seems to move from tape head to the REV/FW IN pins on the IC. Then from there to PRE OUT pins which then circle around to the MIX IN pins. This is I'M GUESSING where the MEGA BASS frequences are "mixed" into the signal. There is unfortunately not a lot of info from what I can see of how this actually works.. but then the MIX OUT pins go into the POWER IN sections of the chip and then finally they are sent out from there to the headphones. In order to hear the frequencies of the MEGA BASS it would make sense that the PRE-OUT is definitely making it to the MIX IN pins since I can hear the MEGA BASS output in my headphones. So it seems like there must be something broken between MIX IN and MIX OUT. Although I am a little dubious about what the heck H.PIN L and R are as well as L.P2. Maybe those are High Pass and Low Pass filters? If so maybe the H.P IN (R) is disconnected somehow. Maybe that's where that oxidation is on the board. If the pin numbers start on the bottom right and go UP to 27 and 28 those WOULD be the the HPIN L and HPIN R. But I don't really know how the pins are numbered. I wish I understood more about how the MEGA BASS circuit works but it's kind of a black box within the IC I think.

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toads said:
But I don't really know how the pins are numbered.
Click to expand...
I'm probably at the end of what I can suggest. However, typically the pin near the black circle (upper left in your pic) is pin 1, then the rest follow counterclockwise.
 
Well I just tried to reflow the pins on the IC without a rework station (tried to use a soldering iron with a chisel tip) and now all the solder has been removed from the pads so the walkman is ruined! I can't believe I just did that! Now I have to explain that I ruined the walkman that was working more or less fine.

I am truly a moron.

Thanks for your help @swechsler. I'm going to go stand in a corner and think about what I've done.
 
elvi said:
Deep breath.
Solder paste will redeposit solder for you.
Click to expand...
Thank you lol. I was so, so mad when I wrote that. I ended up buying a second fx-290w that was also not working and combined them into one working unit! I believe the capstan motor is in need of a rebuild and then I'll need to get a hot air rework station to put the ic back on. Hopefully that will fix the issue but we'll have to see someday in the future. For now I have fixed my error.
 
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