HP LaserJet series - need a schematics of PSU

[Jurek_p]

Hello,

Please help me with the schematics of the power supply unit. The model numer is RG-2500, but I can't find it anywhere...
This power supply is included in the following printers: HP LaserJet 4 / 4M (C2001A / C2021A), HP LaserJet 4 Plus / 4M Plus (C2037A / C2039A), HP LaserJet 5 / 5M /5N (C3916A/C3917A/ C3952A).

https://usermanual.wiki/Hp/HpPrinterC2001AUsersManual549338.731490769.pdf

Thanks a lot.

[tooki]

Check that part number more carefully.

But the chances of finding a schematic are very, very low. It’s unlikely they were ever published, since the power supply is intended to be replaced as a module.

I’d open it and begin doing the typical troubleshooting for a power supply of that age. It’d be unsurprising to find dead electrolytics in something from that era.

[Jurek_p]

Thanks a lot for your answer. The PSU is working fine. I just got this one from recycling and want to use it in a project which needs a +/- 12 VDC supply. This PSU supplies 24VDC and couple of 5VDC outputs. My idea is to modify a 24V output as +/- 12VDC outputs. I'm not sure if it would be as easy as worth doing it. Just as experiment. Without schematics I won't be able to do it, I think.
It would be nice to have about 1.5A from both 12VDC outputs for my purpose.

I have measure the current from 24 VDC output with 10 Ohms load and it's about 2.46A. I think it's a lot for this unit. It's 56W and I don't think it's meant to be pushed that hard. But I don't know... this is probably 50W PSU?

[wasedadoc]

Even if you get the schematic I think you have little chance of modifying it to give +/- 12 Volts at anything near 1 Amp.  The transformer in a switched mode power supply is a key part of the design.

For low very currents you could make a virtual ground at the middle of the existing 24 Volt output using a couple of low value, high wattage resistors.  For higher currents you would need additional active circuitry and power transistors.  Think about it.  If you are taking 1.5 Amps from the +12 side but close to nothing from the -12 side, the overall 24 Volt output is still giving 1.5 Amps.  That "extra" 12 Volts and 1.5 Amps has to go somewhere as 18 Watts of heat.

I suggest you just go on ebay and buy a couple of those modules like in the attached photos.  The 12 Volt 2 Amp one is £5 delivered in the UK. Less then US$15 for two?