SMPS startup problems are frequently caused by dried out electrolytics on the PRIMARY side - the first thing I do with these is replace all the low-voltage electrolytics on the primary side - there are usually only one or two, using 105 deg.C types. This often fixes the problem. Also, the high-value (100K-ish) startup supply resistor going high is another possibility. Secondary-side problems seem rare with small SMPSUs. On Sun, 2 Dec 2001 20:19:37 +1300, you wrote: >Original topic on this May 27 2001 Post by Roman was > > Re: Re: [PIC]:PICSTART+ Hardware problem > >This post and Romans (see below) MAY help people with PICSTART PLUS = startup >problems caused by power supply degradation. > >Got sick of my PICSTART Plus not starting for about 20 minutes after = being >plugged in. >Mine has only two ecaps on secondary side (may be older?) > >Replacing both failed to cure the problem. >The first is 470 uF 16V? and is fed by the diode from the switching = power >supply. The second smooths the output proper and is fed via an inductor = from >the first. The second is 100 uF 25V as Roman says but clearly doesn't = NEED >to >be 25V as the first is 16V and the psu is regulated 9v > >SO - I replaced the second with 1000 uF at ?16v. Brute force but it does= fit >and "almost" sits down on PCB. >This ONLY JUST works. Putting mains on psu first gives 9 volts open cct.= But >when PICSTART is plugged in it powers up "most of the time" but not all = the >time. If not just unplug secondary and reinsert and it usually goes. = Once >going its fine. Clearly the system is marginal. It works for now - I may= go >looking for why some time but don't count on it. Mayhaps the cap's ESR = is >critical to the feedback loop? > >Mayhaps the primary DC supply (about 300 volts) is ripply but I didn't >bother chasing it when this fix (almost) worked. (Small HV caps are less >commonly >to hand here than LV ones). > > > > > Russell McMahon >_____________________________ > > >----- Original Message ----- >From: "Roman Black" >To: >Sent: Sunday, 27 May 2001 21:36 >Subject: Re: [PIC]:PICSTART+ Hardware problem > > >> Seth Fischer wrote: >> > >> > I have been using my new PICSTART PLUS programmer for two days and = have >> > experienced the following problem persistently untill the PICSTART = PLUS >> > will not operate at all: >> > >> > After a number of successful programming cycles I disconnect the >> > PICSTART PLUS dc power lead. When I return to work and reconnect the= dc >> > power lead the power on indicator does not light and MPLAB can not >> > establish communications with the PICSTART PLUS. >> > >> > I measure 9Vdc on the power supply output plug. >> > >> > Any ideas? >> >> >> Yes, it is the same as mine started doing. It's related >> to the ripple level from the PSU. Pull the PSU apart >> and replace the (smallest) electro cap in there, it >> is next to the heatsink(!!), I think it is 100uF 25v. >> There are only 3 caps on the secondary side, probably >> best to replace all 3. >> >> It seems mainly to happen to 240v AC mains countries. >> I also try not to leave mine plugged in to the mains >> all the time, that is BAD, it has no on/off switch... >> :o) >> -Roman >> >> -- >> http://www.piclist.com hint: PICList Posts must start with ONE topic: >> [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads >> >> >> -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu