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Hitachi Projector CP-X275WT Power Supply Question    
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madmanmapper



Joined: 17 Sep 2007
Posts: 36
Location: Chicago, Il, USA

PostPosted: Sun Mar 15, 2015 2:32 pm    Post subject: Hitachi Projector CP-X275WT Power Supply Question Reply with quote

Hi guys. I bought a $20 LCD projector minus bulb, intending to put an LED in it. Have done before with good results, but wanted a fancier system to turn on the LED for this one. Which required probing stuff. Whilst probing stuff, one of my wire clips popped off, and landed smack-dab in the power supply, shorting it, and burning a trace or two.

I have the board repaired to the best of my ability, but apparently the short burned 1 or 2... thingies as well. Wondering if you guys could help me identify them.

They are labelled TH101 and TH102 on the pcb, with a symbol for a resistor. On them, they say 0S S5RI 24 (TH102) and 0S S5RI 25 (TH101). They are wired into the 110v ac circuit entering the power supply, in series with the circuit, one after the other. The only thing that comes to mind for 'TH' is thermistor, which seems unlikely. They do look a bit like some kind of resistor, though. And I seem to recall changing something similar on a PC power supply once, that was NOT a resistor nor a cap... can't remember for the life of me what it was called.

Pics
https://dl.dropboxusercontent.com/u/37540750/hitachipsu1.jpg
https://dl.dropboxusercontent.com/u/37540750/hitachipsu2.jpg

Ideas?
Google

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JTS1957



Joined: 21 Jan 2009
Posts: 2325
Location: Far, Far Away

PostPosted: Sun Mar 15, 2015 3:37 pm    Post subject: Reply with quote

I'd go with 'thermistor.'
You're probably trying to recall an MOV thingy.
And you're also missing a fuse in picture.
madmanmapper



Joined: 17 Sep 2007
Posts: 36
Location: Chicago, Il, USA

PostPosted: Sun Mar 15, 2015 4:05 pm    Post subject: Reply with quote

Quick response, nice. Why would a thermistor be wired in series with 110v ac?

Now that you mention it... yeah, I think it was an MOV. Wouldn't these be MOVs then? Would make far more sense, given how they're used... in line with AC voltage. The one that's not fully broken has 8.3 ohms across it. The other is totally open.

And of course I'm missing a fuse. It popped when the board shorted. >_> I have replacements somewhere.
JTS1957



Joined: 21 Jan 2009
Posts: 2325
Location: Far, Far Away

PostPosted: Sun Mar 15, 2015 4:43 pm    Post subject: Reply with quote

http://www.electronica-pt.com/esquema/func-fileinfo/24615/
http://elektrotanya.com/hitachi_cpx275w_pj550_sm.0518.pdf/download.html
Elektrotanya also has but I've used my two dl's for today - it looks like it may contain a parts list, whereas electronica is TS charts and schematics ONLY.
madmanmapper



Joined: 17 Sep 2007
Posts: 36
Location: Chicago, Il, USA

PostPosted: Sun Mar 15, 2015 5:45 pm    Post subject: Reply with quote

Ah, thank you. The elektrotanya link is the full service manual, which will be very helpful, especially for customizing the lamp setup. Though neither specify just what the heck those thingies are. But here's a screenie of the psu schematic with those thingies pointed out for you. I'm really leaning towards MOVs / varistors. A little unusual for having two of them, no? Isn't there generally only one?

https://dl.dropboxusercontent.com/u/37540750/hitachipsudiagram1.jpg
Google

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JTS1957



Joined: 21 Jan 2009
Posts: 2325
Location: Far, Far Away

PostPosted: Sun Mar 15, 2015 6:13 pm    Post subject: Reply with quote

JTS1957 wrote:
electronica is TS charts and schematics ONLY.

Already had them.

http://en.wikipedia.org/wiki/Varistor
http://en.wikipedia.org/wiki/Thermistor

What you did was drop a piece of metal that, in effect, put a direct short across L101. Something had to give, so the fuse, thermistor and foils took the brunt of the force.
madmanmapper



Joined: 17 Sep 2007
Posts: 36
Location: Chicago, Il, USA

PostPosted: Sun Mar 15, 2015 7:02 pm    Post subject: Reply with quote

So... they're thermistors... that are used in the same manner varistors would be for circuit protection. Got it.

What I did today was steal two, uh, what I thought were varistors (but are probably thermistors) from 2 old computer PSUs, and put them on this board. Apparently one of them is completely open (explains why I replaced that psu some years ago...), so its not making any connection. So how about this: If they're just redundant circuit protection, can't I just bypass them both? The fuse is still there for protection. At least as a temporary test to see if the psu even works any more?
JTS1957



Joined: 21 Jan 2009
Posts: 2325
Location: Far, Far Away

PostPosted: Sun Mar 15, 2015 7:25 pm    Post subject: Reply with quote

For 'Testing" purposes ONLY!

I'd just use the one that's still intact.
madmanmapper



Joined: 17 Sep 2007
Posts: 36
Location: Chicago, Il, USA

PostPosted: Sun Mar 15, 2015 8:34 pm    Post subject: Reply with quote

Well. Bypassed the one dead thermistor, and it popped the fuse. I did some poking around, and found that both sides of the AC circuit were shorted (0.8 ohms). Unsoldered a couple things and eventually found it was the main diode (D101). Stole a diode from one of those PC PSUs and... it works now!

Guess I need to hunt down one more thermistor, and then I can get to work on that LED setup. Thanks for the help, might be back later for some other knick knack stuff with this.
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