HP Laserjet 4L Formatter Board

[BobFBurns]

Hi All

Can anyone point me in the direction of a circuit diagram for the HP 4L formatter board please. Centronics interface has three failed components which cannot easily be identified.

Many thanks.

 

[dkdude]

You say three failing components... How do you know? And whichh ones are they?

If it's an IC and there if is a part number printed on it, then you can use IC-Master to find an equivalent part from other companies:

http://www.icmaster.com/

They require registration, but it's free...

I google'd it and the closest I came was that there is no HP schematics available to the public §;O(

Good luck, though §;O)


Jakob

 

[BobFBurns]

Hi Jakob

Thanks for your prompt reply. I located and identified two of the faulty components (dual diodes) because they showed considerable differences in forward and reverse resistance compared to the other six similar components in the Centronics interface. I can guess at the likely type of component to use as a replacement for these.

However, the third component which was a three legged device was so badly burnt that it fell apart during removal. Impossible to tell if it was a transistor, regulator or whatever. It appears to provide some sort of reference voltage to the protection network but without a working board it is impossible to guess at its function.

I have a full service manual for the 4L but no PCB circuits.

Bob

 

[dkdude]

It could be a reference voltage or a voltage regulator (named 78vv for positive +vv voltages and 79vv for negative ones). Or a transistor. Or somthing completely different.

Without the circuit drawing we're not gonna get further.

That's too bad §;O(

Do you know why it blew up? Maybe something else has gone with it, so it could be cheaper to purchase a new printer (without sounding too clever).


Jakob

 

[BobFBurns]

Hi Jakob

The previous owner tried to force their laptop power plug into the memory expansion socket and it disappeared in a cloud of smoke!!! The fault rippled through the laptop electronics and caused some component failures in the printer centronics protection circuit. I have removed all obviously faulty parts and the Centronics interface now has the correct order of sinkable current - before the repair two of the lines would provide in excess of 100mA current which is way over the top.

As you say, a circuit diagram or a working formatter board is required (I used to be a hardware designer before I changed over to software engineering). Thanks for your interest.

Bob

 

[dkdude]

Ouch, all really went up in smoke I can imagine!!!

Hardware designer! Great -now we're at the same wavelength -nice! §;O)

I'm thinking, that if the circuit board is still intact, then maybe you can draw up that part of the circuit with known parts surrounding the area where the scorched part used to be -then maybe we can reverse engineer it...

-I studied to be an electronic engineer and now I am working as hardware technical services manager -have 5 proficient guys working for me, so there is a chance to get it sorted....

Regards


Jakob

 

[BobFBurns]

The PCB is fine, just the surface mount parts got fried. I must try and find a working Laserjet 4L and measure the formatter board. I think the the 5L uses the same PCB so there is hope yet.

Bob