I am restoring a Sony WM F707 walkman that has been dead on arrival. It does not react to any inputs, on-device or on the remote. I checked for power issues and noticed that of the three voltages this device works with (1,2; 2,4; 3,6 V), only B+ at 1,2V is there. I checked this at some select ICs and the DC-DC converter flex cable header. Both the 3,6 and 2,4 lines show 1,2V only. Now, I don't know if the 3,6 and 2,4 are supposed to be there all the time or are only generated on request (I don't know what the D CTL line stands for). However, I also observed the following: When I press PLAY on the remote, the 3,5V rail shoots up erratically to 2,5-2,9V for as long as I depress the button, wildly fluctuating. Occasionally, I have managed to kick-start the device into action by doing this, presumably because the voltage sometimes reaches the minimum level for the logic to function. I have then taken out the DC-DC converter (the sealed, copper box in the lower right corner of the device) and replace it with a replacement unit out of a spare F707 - to the same effect. Does anyone have some advice on what component failure this behaviour might indicate? As symptoms haven't changed from one DC-DC converter to the other, I'd conclude that the converter is not the culprit. Is there any other component on the mainboard that's critical for the power supply? Thanks!
While searching for a picture of the model that you're working on, I found your other thread from the internet and then I put a couple pictures close up of this model so I have a better idea as to what it is and I thought I'd post another picture of where I found it of this wm-f707 model that I have. It's been years since I've played with these walkmans. I need to find time and check them out again. Some of these in this bin I've checked out but not all of them including this 707 There's just not enough time in the day to do everything.
spitballing since i havent worked on these newer walkman models, but might have an idea what could be wrong taking a bit of a liberty here assuming its meant to be a constant flow of 2.4 and 3.5 volts on those 2 contacts since the manual doesnt state otherwise sooo since they both have voltage issues id guess its something far up the line close to where the power is coming from, which assuming its a steady 1.5v in then the inductor chip L801 is what id start with. can start with checking the 1.3v in on q801 (inductor voltage output). and the capacitor leading to ground i guess, but those smds fail pretty rarely if its all fine there, then just keep following the line down the list of components. didnt draw out all of the paths or else itd be a jumble of red lines lol, should be a good place to get started though also, if it was the inductor that failed it would explain your symptoms. though i do find it kinda hard to imagine since ive never heard of one failing on a walkman before
Thanks, @Squiggly. I appreciate your support. Unfortunately, the matter is more complicated. The DDC FLEXIBLE BOARD is what's in the copper box in the top photo. This thing is sealed shut and I would probably need a Dremel to open it. This is the DC-DC converter and it can be removed in its entirety. I replaced it with a second converter and it resulted in the exact same error. Because of this and because I noted, as stated above, that the 3,5 and 2,4 V rails *DO* rise up to required levels upon long-pressing the aforementioned remote buttons, I do think the converter is not the culprit. Rather, something outside the converter might be hindering the voltage ramp-up. For the moment I do not know for sure what that is, but I have a hunch: C328 is an electrolytic that I haven't replaced yet and it's in the path from the 2,4 V line. If it has gone open and is pulling down that rail, I'd assume this might throw the converter off-balance. I'll have a closer look at this one next week.
oh gotcha, guess i missed that part in your post of course itd be the dreaded 220uf 4v capacitor, bane of all miniature 80s walkmans prone to fail and hard to replace. still have yet to figure out how well smd replacements compare those little things have got to be my #1 opp as the audio is starting to fade on all my old 80s players with them being the cause if you replace it with an smd lemme know how it works out, really need to finish up recapping mine and never got around to finishing but curious how they compare
I replaced it, but there was no change in behaviour, unfortunately, When I accidentally got the Walkman working one time, I noticed that the 3,5V apparently are there the whole time - they are not generated “on demand”. That said, it would seem that the DC-DC converter might indeed be the issue. So I’ll have to crack it open some time soon…
sounds like its gonna turn into a bit of a basket case, cant really see how they sealed the copper box shut so guess youre gonna have to get creative best of luck tryina crack that thing open by the way, can only imagine how big a pain thats gonna turn into. my guess is its just sealed shut with solder so you might be able to melt the seam with a hot air station
