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
