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Bolle

SE/30 Sony CR-44 PSU unstable voltage output

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This is my first Sony PSU that is actually giving me problems even after a recap...

 

Voltages were pretty low to begin with but still in the workable range. I got some pretty nasty screen wobble whenever the disk was accessed or something else taxed the 12V or 5V line.

I started by replacing all caps in the PSU and adjusting the pot in the PSU and it is now outputting a nice 5.07V and 12.18V when idling with a logicboard connected.

 

However the screen still wobbles (less than before but still there) if there is any change in load on one of the power lines (disk access, Finder interactions, etc...)

Screen still wobbles on disk access even if I use an external SCSI disk and disconnect the internal drive so I have the feeling it is a problem on the 5V line.

Made a short example clip where you can see the screen size changing when I click the scroll bar thingy in a Finder window for example:

 

https://www.dropbox.com/s/6mdqf9xwgntbyiv/SE30 PSU.mov

 

You can see that the 12V line drops once I click on it (5V line raises by .1V) and it raises back to 12.2V-ish once I release the mouse again (5V drops again by .1V)

 

 

When using a different power supply everything is fine, so I would like to rule out logicboard, analogboard and everything else that's not the PSU :tongue:

 

Any ideas how to approach any further troubleshooting?

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Johnnya had the same issue. I have his PSU, but haven't had time to really dig into it yet. I'm suspecting the main switching transistors. I also found a faulty diode near the PWM chip.

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Hi guys,

I get the same wobble on my se/30 and its been getting worse over the last year. I’ve brought a new board/psu which i was planning to recap before putting it in to stop the wobble. I’d be pretty gutted to do all that and still have the wobble :/ should i change the transistors and diodes as well.  If you could keep me posted on how you get on as it sounds the same and as a novice this is a big deal for me No idea about metres and haven’t even ordered soldering iron yet.

 

hope you get it sorted Bolle :)

 

Cheers Neal

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It looks like the 3122V voltage regulator in my PSU is dead. Desoldered it and tested it out of circuit and it does not output any voltage at all.

The +12V Sweep output is only getting the "uncleaned" +12V Disk rail through the two diodes D264 and D254.

Not quite sure why they did things this way... did they expect the 3122V to fail and they wanted things to keep running anyways? :?:

If the extra regulator works the small fluctuations in the 5V and 12V disk rails shouldn't matter anymore as the sweep circuit will get clean 12V from the regulators output.

Any modern replacements for that one available or shall I go hunt eBay for a hopefully non-fake NOS one?

Edited by Bolle

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Got a good deal on two SI3122V's on eBay.

Wobbly screen is gone, issue fixed.

 

Still puzzles me why they built it to still power the 12V-sweep rail even when that regulator dies by using the 12V-disk rail instead.

Bildschirmfoto 2019-10-08 um 18.26.31.png

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Interested in the outcome of your research, Bolle...

My SE/30 also has this issue but somehow it's worse. The wiggling occurs on about 1cm. Mind you, the Analog board is still 100% stock (PSU, LB recapped).

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You can easily test if the SI3122 is still good using a bench power supply once you desoldered it.

Hook up ground to pin 1 and some voltage that is above 12V to pin 3 and you should be able to measure 12-14V on pin 2.

At first you might probably want to test if the problem moves to another machine if you move the power supply over to be sure it's not related to your analog board.

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