Ricoh SP 150w PSU repair

[herved]

Hello everyone,

I'm trying to repair a 24V PSU from a Ricoh SP 150w printer.
So far I found and replaced:
- a burnt 33Ohms 1W resistor (R820 - top side next to main cap)
- a shorted mosfet (Q801 - top side on heatsink)
- 2 shorted optocouplers (U801, U201 - top side)
- a burnt/chipped? (didn't read any resistance) SMD resistor (R828 - back side next to the PWM IC)
- the PWM controller (IC801 - back side)

There is no output voltage at all.
I do get a stable voltage at the main capacitor (320V) but I think the PFC is not working.

The PWM IC was marked 83H08P which is supposedly an OB2283 PWM controller (possibly a copy of the original?). VCC at this IC reads 6.3V which I think is not enough to get it started (needs 12-28V).

The board looks quite different than the standard schematic from the datasheet. I don't really know how it is supposed to receive that voltage.
I tested a lot of SMD components at the back (resistors, diodes, caps,...) which were ok so I don't see what else I can try from here.
Any ideas?


Thank you ,
Hervé

----

PS: As you can see I damaged the back with the hot air station (too hot) trying to remove the diode... Because of this the board may be compromized a bit, but the traces are still intact, so maybe I can still learn something from it.

PS2: Here is a link to a russian forum with much better images than I can produce. Especially the last post.

[lotas]

Re: Ricoh SP 150w PSU repair

You don't have resistor R827.

[herved]

Re: Ricoh SP 150w PSU repair

Ah , sorry that image - 1665789398015 (1).jpg - is a bit outdated.
I replaced R827, it is now there, see 1667434197.jpg.
It is a 470 Ohm resistor.

[lotas]

Re: Ricoh SP 150w PSU repair

Check these resistors, the resistance has not changed in them. And where did you get the idea that PFC is present in this circuit?

[lotas]

Re: Ricoh SP 150w PSU repair

Check these capacitors for ESR.

[herved]

Re: Ricoh SP 150w PSU repair

Here are in-circuit measurements:
- R826 = 10K (looks ok)
- D804 = 0.52 Vdrop and blocking in the other dir (looks ok)
- R804-805-824-812 = all read ~0.70-0.75M (looks ok)

I also checked carefully this path earlier.
Here are the voltages when the board is powered on to 230V.

And where did you get the idea that PFC is present in this circuit?

Isn't it what a PWM controller is an SMPS does? Like we have here?
I'm a noob please correct me if I'm wrong

[herved]

Re: Ricoh SP 150w PSU repair

C807 (markings 2,2 uF, 50V) => 2,371 uF | ESR=1,52 Ohms
C833 (markings 10 uF, 50V) => 10,22 uF | ESR= 0,49 Ohms

C803 main cap (markings 47 uF, 450V) => 43,01 uF | ESR= 0,63 Ohms

[sam_sam_sam]

Re: Ricoh SP 150w PSU repair

The 2.2uf cap might be bad I like to see low value uf cap lower than 1.0 but this is just me

[herved]

Re: Ricoh SP 150w PSU repair

Ok I replaced both caps, I still get ~6.3V on VCC of that PWM chip.
But I do get some output voltages in fact:
- 3,4V on "+24VS"
- 2.7V on "AC test" which seems to be "pulsing" to a higher voltage (+24V?) every 2 seconds or so

I wonder what that "AC test" means.
Is this a switch to turn it on by shorting it to ground or similar? Like on an ATX PSU?
I can't really understand the board/schematic.
It goes to a transistor marked (K1N D1) which is connected to one of the optocoupler (emitter-collector).
Any ideas?

I'll try to put it back in the printer but I doubt it will make a difference.

Thanks a lot,
Hervé

[lotas]

Re: Ricoh SP 150w PSU repair

Yes, some power supplies do not run at full power without load.

[herved]

Re: Ricoh SP 150w PSU repair

I put the PSU back in the printer but it is not starting.

Before replacing the caps I tried to put a load (24V motor) but it didn't work either (I could try again). Hence why I'm also wondering about this "AC test" pin.
I'm thinking something else is bad in this PSU but I reached my limit on how to troubleshoot it. I don't know what else to check, I believe I tested most components on this board.

[R_J]

Re: Ricoh SP 150w PSU repair

ac test is a signal from the power supply that tells the printer it is plugged in.
Check R827, (between mosfet source and pwm ic CS pin) Also check R811? (marked 200) 20Ω resistor from the transformers feedback, that supplies the vcc run voltage.

[lotas]

Re: Ricoh SP 150w PSU repair

Well, if you have checked everything, try replacing the "reference voltage source" - TL431.

[herved]

Re: Ricoh SP 150w PSU repair

I just tested the TL431 (5V on Ref and Cathode and I get 2.5V out).
So I assume it is ok. I don't see any reason to replace it, don't have any in stock either.

Thanks,
Hervé

[herved]

Re: Ricoh SP 150w PSU repair

SUCCESS !!! The PSU and printer are now working!

I read several people who had to chop off (or lift) pin 5 after getting a replacement OB2283 PWM controller chip.
Which I eventually did in a desperate attempt, after testing literally EVERYTHING on this board.
And... it works now.
I don't know if there is any impact doing so though... Anyone knows?

I guess it is not exactly the same chip as the one that was there originally.
I had ordered it on aliexpress here https://www.aliexpress.com/item/33045121475.html
It is advertised as "OB2283MP OB2283 SOT23-6 Chipset".

I spent a lot of time and it may be just a 100€ printer, but I learned a LOT about electronics and SMPS while attempting to fix this. I even sorted properly by stash of electronic parts. This is great!
Thank you lotas, sam_sam_sam, R_J for the support

[herved]

Re: Ricoh SP 150w PSU repair

I'm also interested to hear if anyone has theories about what caused this PSU to blow up though. Do MOSFETS just short like this usually? Because of age? or voltage spikes? Lack of protection in the circuit design?

It blew up upon pressing the power button.

[R_J]

Re: Ricoh SP 150w PSU repair

looks like "several people" see no purpose for protection for the power supply and can't find the cause for the problem so they just disconnect pin5 (prt) There is likely still a problem so it will be interesting how long it lasts. Let us know.

[herved]

Re: Ricoh SP 150w PSU repair

Sorry I'm far from an expert.
You're right, it probably bypasses some protection...

Am I correct to assume that the TL431 is good if it outputs 2.5V?
I used the method suggested by LER here https://www.youtube.com/watch?v=LvGehyWLS80

Any suggestions on what else to test?

Thanks