I've recently picked up one of each of the above models. They are in generally good cosmetic condition, but all three are non-starters. No power, no response to buttons, no LCD display (on the tuner models). I've seen other threads suggesting that this is not uncommon on this model series, but I never saw a resolution. I already have good experience in Walkman repair / restoration, but the WM-70x series are new to me. Before I dive headlong into troubleshooting and electrical diagnostics, does anyone happen to know if there is a common / typical fault with these models that makes them play dead? I've only opened the F701C so far. Confirmed that power is at least getting to the main board, but current draw is practically zero (less than 1mA). It doesn't appear to contain any electrolytic caps whatsoever, so that rules out the usual prime suspect! Any pointers appreciated!
Hi! Did you see this post by Valentin? https://stereo2go.com/forums/thread...orders-common-problems.7535/page-2#post-59825
Thanks. No, I hadn't seen that, but nothing in there that would explain the complete lack of response from all three of these units. They don't respond to the remote control either, so I'm pretty sure it's not simply bad contacts in the logic control buttons. Here's the inside of the F701C. Some evidence of slight corrosion from battery leakage, but I've checked continuity of a few of the worst-looking PCB traces and they all seem intact so far. I'll keep looking!
If you ever find a solution to this, do let me know. So far, I have encountered this issue only with several F707, and it still has me stumped. I have been able to trace it to the DC-DC converter (the copper box in the lower right). Have a look at the voltages going to and from the converter when idle, when pressing a button, and when under load (the flex cable). Mine is missing the 3,5 and 2,4V rails. When pressing a button, the 3,5V rail is wildly fluctuating up to 2,6V or so, but never reaching 3,5V. Very rarely, if you keep pressing a button, it will eventually turn on, but other functions will remain missing. So far I have been unable to figure out which part on the folded converter board has failed (as I presume). I am considering replacing several key components by trial-and-error. I suspect some transistors, but I am really not sure. Also have a look here: https://stereo2go.com/forums/threads/sony-wm-f707-restoration-dc-dc-converter-issue.9687/#post-78035
@Fulltimehuman, thanks, yes your thread was one of the ones I'd seen when searching for info about this problem. I hoped you'd found the solution in the meantime! I have done some further dismantling of the F701C. Discovered a flex PCB that I hadn't originally spotted, tightly folded and tucked in around the battery compartment, linking the motor and DC-DC to the main board. I thought it was Game Over when I saw the state of this - it's ravaged from battery leakage... (photos below are after cleaning, it looked even worse to begin with). But amazingly it turns out that all nine traces are still intact, and there are no shorts - so I've cleaned it thoroughly, coated it in lacquer*, re-assembled everything and re-checked continuity - but still no life from the unit. I've looked at the voltages on the DC-DC outputs and they are 1.5V and about 1.3V. They don't respond to any button presses. I can see from a quick glance at the schematic in the service manual that DDC_CTL will enable the converter when pulled low. So I have tried shorting this line to ground, but there's still no movement of the output rail voltages. This seems to confirm the DC-DC converter is at fault. I will have a go at opening this next. This is turning into a bit of a mission already... * my wife's nail polish
@nutronic, how did you figure out that the CTL line needs to be pulled low to turn on the DCDC-converter? Is Q801 doing the pulling? I have been wondering what this line does for a while, but that would be logical. (Surprise, I'm just a hobbyist!). I'll have to check with mine to see if there's corresponding behavior. (I also have an F701c that's still powering on. I was unaware that it also has a DCDC-converter that produces three output rails. Maybe I'll switch this one in or check for the proper behavior on this one. I have it on the bench and should be able to do this quickly.) So, are you missing both the 2.4V and 3.5V lines? That your ICs would obviously having issues. The DCDC-converter is fairly easy to open – easier than you might think. (It's just clamped-shut, not welded.) On the F707 the box contains a flexible board that is folded up multiple times (disregard the red circle): In the picture are three layers of the PCB that get folded on top of each other and then stuffed into the copper box. I tested all the components in the box, but – possibly due to incompetence of the tester – my results were inconclusive. Two diodes may be faulty (O.L. in both directions) and one transistor might also be faulty. I am planning to replace these and possibly other components, but I still have to order the parts. This might take a while. That's where I am at the moment. I shelved the project until the parts arrive, as I am working on other devices in the meantime. However, the F707 is a true beauty and I'd love to get it working again.
