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" <fastvid@EZY.NET.AU>
To: <PICLIST@MITVMA.MIT.EDU>
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
>
> --
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>
>
>

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