Hi guys sorry to jump in but I have found in my NTSC C128 on the output 12V portion of the regulator (U59) has a dead short). I found one in c111 a tiny cap but there's still something shorted, of course not applying power, power source completely unplugged. I was told the 12V section powers the SID and VIC. BTW I replaced all filter caps and the regulator on U59, I was also wondering what the filtering is so thanks question answered. I had replaced the fried Full Wave bridge rectifier (was blowing fuse in Power source). Like on C64 or C128 like in the area where the RAM chips are located the kind of flat light tan 2 or 3pin components are these ceramic or Tantilum? I'm hoping it's In the VIC video circuit because it did fry the VIC chip. I tested this in one of my NTSC 128 DCR had a blank snowy display matched this with Ray Carlsens handy info on finding bad MOS chips. So to find the short in C111 I set my meter for OHMS using the beeper and this is how I found this component to be shorted. Can you check any component right in the circuit or does it need to be desoldered? Maybe it's just ready for the parts bin too but just wondering if it could possibly be ressurected. Terry Raymond On Aug 21, 2017 4:05 PM, <silverdr@wfmh.org.pl> wrote: > > > On 2017-08-21, at 23:07, Mike Stein <mhs.stein@gmail.com> wrote: > > > > How is any cap across the IC's power pins not "filtering the power > rail(s)"? > > The main, desired effect of the typical for digital ICs 47nF/100nF bypass > cap is limited to a relatively small distance. That's why you put them > close to the component rather than at the power connector common for the > whole board. That's what I call bypass cap. You can have other, higher > capacitance cap, which bypass/filter other frequencies... > > > If you look along the IC's supply rail you will probably also come > across some 10 - 100uf caps across the power rails, maybe even right beside > a ceramic; are they filters or bypasses? As I said, the only difference is > the frequency they're intended to 'bypass' which will determine the > apppropriate type and location. > > ... and you can have (usually even more bigger) ones that "filter" much > lower frequencies for the whole board or section and are therefore placed > close to the supply points of the board / section rather than the small > component. > > > But if you want to call electrolytics and tantalums "filters" and > ceramics "bypasses" that's OK; we'll know what you mean... ;-) > > :-) No, not exactly. My arguably bad old habit is to call the small ones, > placed out of necessity next to the component / IC and filtering mostly the > respective component "bypasses" and those which are used to provide > filtering for larger sections "filters". It doesn't have much to do with > the type/manufacturing process of the capacitor. > > -- > SD! - http://e4aws.silverdr.com/ > > > Message was sent through the cbm-hackers mailing list > Message was sent through the cbm-hackers mailing listReceived on 2017-08-22 21:03:58
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