Laserjet III DC power supply probs

[Ben Myers]

Nothing wrong with reinforcing what others have already stated. It's not like
the majority rules, but... Ben Myers

So stated by other postings in this thread... Ben Myers

Sorry ... guess I came in late.

 

[ato_zee]

Nothing wrong with reinforcing what others have already stated. It's not
like the majority rules, but... Ben Myers

Replacing parts at random, without proper diagnosis, gets expensive.
Garages tend to do this as well, at prohibative charges.
With switchmodes going into spasm lift/break one rail at a time until
it doesn't spasm/shutdown. AFAIR the original post did not point
exclusively to the PSU. Just that it shut down during power up.

 

[GanjaTron]

With switchmodes going into spasm lift/break one rail at a time until
it doesn't spasm/shutdown.

You mean actually *severing* paths on the PCB? Isn't that rather
drastic? :^)

AFAIR the original post did not point
exclusively to the PSU. Just that it shut down during power up.

It shuts down even w/o load (DC controller & motor unplugged) so
there's *gotta* be sumptin' wrong with it...

The two optocouplers (TLP634) were mentioned -- anyone got a pinout or
point me to a data sheet? Apparently they're not readily available for
download (at least where I looked). Thanks!

--GanjaTron

 

[ato_zee]

You mean actually *severing* paths on the PCB? Isn't that rather
drastic? :^)

Usually you can unsolder one connection, vith a spring loaded
piston type heated solder sucker, or unsolder the whole
rectifier for each rail. Then replace PSU and switch on, if it stays
up, you have found the overloaded rail. Check for low
resistance across that rail, do a bit of tracing to see if you
can split the rail further. You can cut tracks, it's knackered
anyway, so you have nothing to lose, then restore them with
a soldered bridging wire. But cutting tracks is a last resort.

 

[John Knowles]

Hi, I asked in another post for information on the DC power supply. I would
like to find a schematic. I tried ESI but can't get anywhere!

John Knowles

 

[NSM]

You mean actually *severing* paths on the PCB? Isn't that rather
drastic? :^)

Standard repair method.

 

[ato_zee]

Standard repair method.

The DC power supply feeds the rest of the printer,
lift the outputs, one by one, at the socket the PSU plugs into. If it's
an overload in one of the modules, it'll stop shutting down. The
PSU shutting down may only be a symptom of trouble elsewhere.

 

[CJT]

Standard repair method.

Perhaps in some circles.

 

[NSM]

NSM wrote:

Perhaps in some circles.

The circles competent repairmen travel in, yes.