Author Topic: Help for open frame dual output PSU - model FSP012-2P01  (Read 1011 times)

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Offline CaviaTopic starter

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Help for open frame dual output PSU - model FSP012-2P01
« on: April 05, 2023, 04:02:07 pm »
Hello,

I'm trying to repair an old (retired) open frame dual output PSU: model FSP012-2P01.
This model is commonly found inside old Extron devices (i.e. 201Rxi, DVI-RGB 150, and more). Since Extron does not provide any schematics (as per company policy), I need some experienced soul that can help me debug the problem (I also contacted FSP asking for the schematics of this retired device, but I got no answer so far).

Let's jump into some details. The model FSP012-2P01 (produced by FSP) is a dual-output PSU with the following outputs: 5V at 1.5A and -5V at 1A.
Note: Regarding a possible substitution with a similar device, the only candidate I found is a Meanwell PD-2505 which unfortunately does not fit into the Extron case. I may keep the power supply outside the Extron in a 3D printed case and route the cables to the logic board, but I would like to keep this option as the last solution.

The faulty PSU is showing the usual ticking [tik tik tik] cyclic-reset behavior. I've already replaced all the capacitors, checked the diod+high resistor (measured 15kOhms) line next to the transformer and looked for shorts. Could not find the problem  |O
As I'm not an electrical engineer (or expert), I'm a bit lost now. Any help would be greatly appreciated. If needed, I can setup a video call with anyone who wants to help me live (I have a streaming position at my bench).

Here are some pictures of the PSU.

Thanks all.
 

Offline voltsandjolts

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Re: Help for open frame dual output PSU - model FSP012-2P01
« Reply #1 on: April 05, 2023, 04:25:46 pm »
Check as many passives and diodes as you can in circuit.
Then I would probably try replacing Q10 and U30 if you can get new ones. What are they?
 

Offline wraper

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Re: Help for open frame dual output PSU - model FSP012-2P01
« Reply #2 on: April 05, 2023, 04:29:57 pm »
You say replaced all caps, but did you replace small electrolytic cap on primary side, just in case? Check if diodes on secondary side are not shorted.
 

Offline wraper

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Re: Help for open frame dual output PSU - model FSP012-2P01
« Reply #3 on: April 05, 2023, 04:34:08 pm »
Check as many passives and diodes as you can in circuit.
Then I would probably try replacing Q10 and U30 if you can get new ones. What are they?
Q10 would simply short and blow the fuse when fails. Also does not look like UC3842 issue. I suggest checking its datasheet for typical schematic. This also could be an issue with resistor on it high voltage power input or faulty diode from auxiliary transformer winding.
 

Offline FIXITNOW2003

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Offline CaviaTopic starter

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Re: Help for open frame dual output PSU - model FSP012-2P01
« Reply #5 on: April 06, 2023, 06:23:57 pm »
Hello

@wraper, @voltsandjolts

Diodes report:
All diodes work as intended.

@voltsandjolts
Q10 is a Fairchild SSS4N60B 600V N-Channel MOSFET
U30 is a STMicroelectronics UC3842B PWM Controller
Schematics are attached.
« Last Edit: April 06, 2023, 08:39:03 pm by Cavia »
 

Offline CaviaTopic starter

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Re: Help for open frame dual output PSU - model FSP012-2P01
« Reply #6 on: May 09, 2023, 04:01:05 pm »
Hello, some updates.

I've replaced Q10 and U30 with new parts. The PSU is still cycle-resetting.

Interesting behavior: I didn't work on this circuit for a long time. When I took it again, I immediately replaced Q10 and tested the PSU (first cold boot in a long time).
The PSU started perfectly (no reset) and it was outputting steady 5V DC and -4.7V DC. As soon as I turned it off, and on again, the PSU was showing the issue again and never restarted correctly.

Not sure what to do next. Any help?

Thanks.
 

Offline CaviaTopic starter

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Re: Help for open frame dual output PSU - model FSP012-2P01
« Reply #7 on: May 12, 2023, 11:04:22 pm »
Updates:

Following some suggestions on Youtube, I measured the DC voltage across the diodes in the secondary part of the circuit: D60 is carrying 5V (ofc it's oscillating due to the circuit reset), while D50 measures 0.330V. The transformer is outputting on all 5 pins 87.1V AC.
In the feedback circuit, the DC voltage across the input pins (1,2) of the optocoupler PC20 shows a fluctuating 1.0-1.1V, while the output pins shows an unreadable DC voltage (random values).

If anyone can spot the problem, or a direction to debug it pls let me know.

Thanks.
 

Offline CaviaTopic starter

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Re: Help for open frame dual output PSU - model FSP012-2P01
« Reply #8 on: May 15, 2023, 01:47:05 pm »
Updates:

I've replaced the Optocoupler PC20 (a classic model 817A), and the Programmable Shunt Regulator IC30 (model KA431A). Still same issue. I'm not sure if the problem is in the feedback area, or the secondary part (after the transformer).

This is challenging :(
« Last Edit: May 15, 2023, 04:16:04 pm by Cavia »
 


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