🚀 go-pugleaf

Rudolf Ladyzhenskii wrote:
> 
> In this case, get datasheet for 3842 (from Motorola -- UC3842).

It is burnt into my retinas!

> Make sure that its VCC is 12V. Pin7 from memory.

Vcc is not critical (within limits).  It is clamped to 30V by the chip. 
Usually does not get that high.

> Also check/replace capacitors in primary.

Yep.  Done!

> 
> If you find that VCC to 3842 pulses, I would suspect fault outside of PS
> primary.
> 

Vcc is varying due to change in loading but not pulsing.  I am sure it
is not dropping below a threshold wich will cause the chip to shut down.


> Rudolf
> 
> "Alan Liefting" <aliefting@ihug.co.nz> wrote in message
> news:3C96692D.587C9095@ihug.co.nz...
> > I am almost 100% sure that it is a PSU fault.  The monitor will work
> > occasionally.  The EHT is coming up.  The PSU control ic is not shutting
> > down due to overcurrent.  There is an additional bit of circuitry that
> > controls the 3842 chip.  I think it is for power save.  I am sure that
> > this is the area where the fault is.
> >
> > Alan Liefting
> >
> > Rudolf Ladyzhenskii wrote:
> > >
> > > Check horizontal circuitry.
> > >
> > > Rudolf
> > >
> > > "Alan Liefting" <aliefting@ihug.co.nz> wrote in message
> > > news:3C965925.4A3EA9E4@ihug.co.nz...
> > > > Hello All,
> > > >
> > > > I have the above monitor which is pulsing.  The power supply is coming
> > > > up and shutting down a couple of times per second.  It is definitely a
> > > > power supply fault.  Voltage control is done on primary.  Disconnected
> > > > optocoupler which is for power supply standby.  Still no difference.
> > > > Replaced control capacitor.  No difference.  Replaced opto and UC3842
> > > > control ic.  Still no difference.  Replaced a capacitor in an obscure
> > > > bit of circuitry and came right.  Monitor then failed on test!
> > > >
> > > > FCC ID DK4M1566
> > > >
> > > > HELP??!!
> > > >
> > > > Alan Liefting