@Fulltimehuman thanks very much for the tips here, I’ll definitely get on the SMDs and see how I go. I’m kind of hoping the traces aren’t toast to help eliminate that. There must be a fix! But yes I’ve followed how much work you’ve done so I’m under no illusions that it’s a tricky one!
Hi @nutronic amazing work on reading the schematics! That all makes perfect sense. I’ll start by getting the caps and resistors changed and see what that returns. I too have a few scrapped units that should yield some parts. Does your f707 totally work now?
Thanks @Seb, yes my F707 is working perfectly now. It needed a mechanical overhaul as well (mostly routine stuff, cleaning and lubrication), and some careful bending / twisting of the head armature to get good azimuth alignment. The more time spent on a restoration, the more satisfying it is to listen to when it’s complete, that’s what I enjoy about this hobby. I’ve certainly had my money’s worth out of these two units (F707 and F701C) - still yet to open up my R707, I wonder what challenges that will have in store for me!
@nutronic I've started the repairs and decided on bridging R719 and R720 and now all the buttons work!! Definitely wouldn't have got here without your help so I'm SUPER grateful! I also realised that the band change and stop/radio off button require a longer press than the others so that did have me stumped at first.. The radio comes through loud and clear (sounds great through the 742's) I will need to set up the EU/UK freq setting as it's defaulted to 76-90MHZ funnily enough TV band preset one picks up Capital 95.8..I saw a write up on how to change the area setting so i'll give it a go. The tape sound very good mechanically, low W&F new belt from Deck Tech cleaned up pinch and head. But it's very quiet and thin/distorted so obviously that must be the caps that @Fulltimehuman describes in his very good tutorial. Did you change all the caps? the blue and black as well as the silver ones? I'm just wondering which ones would cause the audio issues on the tape. I'm guessing the problem is from tape head to amp as the radio sounds fine? I enjoy doing these restos too very therapeutic (and occasionally frustrating!) I must admit you both really made this an easy one for me though.... I've mainly been doing the 100 series, a few Wm-30's and 20's and a Wm-75 so it's fun to do something new.
@Seb that's fantastic! When I discovered this issue it seemed so obscure - I'm amazed it has turned out to affect more than one unit. Still not exactly sure which component has drifted with age to cause these units to stop working - although as I say, it looks like the design was very marginal even when new. The sound quality issues will be the 47uF SMD caps (C106/206), the electrolyte will have dried up (or leaked) causing them to go high-ESR. The through-hole electrolytics should be fine, they at least they measured ok on my unit. One day I will get around to sharing my DIY method for testing electrolytic caps in-situ...
@nutronic yes especially as the resistors show as on spec when tested. I think your posts are going to save a lot of 70x’s! Going to order the C106/C206 SMDs probably try and use two soldering irons to get them out.. I tested C407 as it was easy to get out and it showed 167uf should be 220 so I might change that too.. Definitely interested in your in-circuit method..keep us posted! Huge thanks again for now⭐️
