Just updating this thread with my latest attempts to make this PSU usable.
I had already upgraded the knackered capacitors to 105deg C Panasonic ones. 2200uF/25V ---> 6800uF/35V Panasonic TSHA 22uf/25V ---> 1500uF/10V Panasonic FC Using just one 78S05 5V regulator (the 2A version) as I described previously, did not work as it just overheated. I then used another 78S05 but with a 3V zener diode on its ground terminal, making it an 8V regulator. The two regulators were connected in series. This was quite easy to do as one of the regulators has a wire jumper connecting its output to the PSU output. You can just remove this and connect a wire to the input of the 5V regulator, meaning you only have to cut one track, that being the one already feeding the input to the 5v regulator. I also connected a capacitor across the 8V feed between the two regulators (I used Nichicon PL 100uF/16v which are small enough to go on the underside). This setup worked fine for half an hour or so, but the 8V regulator overheated and shut down eventually. It was insufficiently thermally coupled to the heatsink because I had to use a thermal pad to electrically isolate it from the heatsink. The tabs of 78xx regulators are at ground potential but I'd lifted the ground of one to 3V to get 8V out so this was necessary. Finally, I got a proper 7808 (1.5A version) and used that, removing the zener diode. Both regulators are now properly bolted to the heatsink (and I applied fresh heat-transfer compound too). I also followed afblaster's lead from an earlier post and removed some of the ventilation slats in the casing (top and bottom) and there's proper convection in the case now. It's been running non-stop for 24 hours now and gets hot but not as much as originally. The main problem still, is that the secondary voltage of the transformer is just way too high. It's 13V unloaded, dropping to 11.2V with the Squeezebox playing music over wi-fi. Using the 7808 and 7805, I'm sharing the power dissipation equally across both regulators and both sides of the heatsink. They are both dropping 3V. Ideally, the unregulated voltage would be 8V... or even 7V and you could use one low drop-out regulator and it would barely get warm. As it stands, although my PSU appears to be fixed, I'm still dumping more power as heat than the Squeezebox is consuming! Glenn -- Glenn2 ------------------------------------------------------------------------ Glenn2's Profile: http://forums.slimdevices.com/member.php?userid=19286 View this thread: http://forums.slimdevices.com/showthread.php?t=61090 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
