Laserjet III DC power supply probs

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.

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

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

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.

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

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.

Perhaps in some circles.

The circles competent repairmen travel in, yes.