Identifying component and some pointers to repair an ALPS printer PSU.

I just imported an ALPS MD5000 printer from the USA and stupidly forgot to plug it in to my 240>110 transformer before plugging it in ...BANG went the fuse and at least one component on the PSU board....(you get used to everything being auto-sensing these days!).

The printer was new, but at least 5 years old (these printers are unique in that they are capable opf printing white thanks to a unique ribbon cartridge system), they are hard to come by and cost me quite a bit to get here..trouble is that options for 'professional' repair here are very limited (alps only service in the USA), which means that I am going to have to fix it myself (I can solder and have done some electronics in my time - mainly kit build stuff)..

Looking at the board, it seems (from visual inspection at least) that in addition to the fuse, the next component in line (which is what I can't identify) has also blown (I am hoping that this will be it, but one thing at at time!).

The part is a mystery though. My guess is that it is a thermal fuse or Transorb (not sure whether these work with AC at all). Markings on it are 7C241 49P (with the symbol 'SA' in a circle). I have tried all the obvious combinations (googled endlessly), but no luck.

Can anyone shed any light? As I say it is directly inline after the 4A fuse and the marking on the board looks like a resistor, but with one set less Squiggles (like a Z on its side). The board is marked 'Z1' for the component (all other components are marked as ususal Cn for Caps, Rn for resistors etc).

I have posted some images of these here :

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Any help would be gratefully received.

Reply to
ben
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It's a 'transorb' alright. You can tell since it's connected across live and neutral ( see the pcb tracking ).

Can't decode the part number for you but the energy rating of these is determined largely by size anyway. Fitting a larger one won't hurt either. It won't hurt not to have anything fitted there though for now since it only does anything under overvoltage conditions ! Ahem ! Now do remember the autotransformer this time !

It's just possible that it may have saved the rest. If not I'd suspect Q2 for possible overvoltage damage. Dunno about Q1. trying to fathom the circuit from looking at the board.

What's the component marking on Q1 and Q2 anyway ?

Do replace the fuse with exactly the same part btw. I notice that the board doesn't state fast or slow type. If you still have the blown fuse check the end cap. T = 'time lag' ( slow ) and F = fast.

Graham

Reply to
Pooh Bear

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and much more than u wanted to know from one manu:

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The 'sa in a circle' is actually the safety designation "CSA" (Canadian Standards Association), a certification listing like UL.

Hard to see the left logo leg, but the '7' looks like a triangle to me. It, along with the other funky E character would be the manufacturer logo and/or plant markings. I can't be certain about your MOV's rating, but the '241' suggests it's a 240-volt. The '49p' may be the date code or the transient energy joule rating (49).

Reply to
Ray L. Volts

Great, thanks to you both for the help :-)

But of the two which should I use - a Transorb or a Varistor (it looks to me like they are more-or-less interchangeable)?

Assuming that I can't find the actual direct replacement, can you suggest a value for the alternative Transorb or Varistor (the fuse is rated to 4 Amps and was quick blow by the way).

Thanks again.

Reply to
ben

Transorb is simply a trade name owned by some company for varistors.

Well, it's unclear if the varistor was indeed 240V. It shouldn't have blown if it was. It might be easier to ask who you buy components from. I can point you in the direction of Farnell but without an account the minimum order is £20 .

Remember, it won't hurt if the varistor's not there right now. It's only needed to deal with overvoltages.

The fuse look like it was 20x5mm size and you should get one specced at 250V with a F4A (L) current rating.

Graham

Reply to
Pooh Bear

Thanks Graham. I actually have a trade account with Farnell, so that shouldn't be a problem (we always need other things at work!).

If you can humour me for a moment though - if the PSU was designed for

110V (and I will remember to use the trasnformer this time...), is it not a 110V or thereabouts Varistor that I want? I've ben studying a Varistor selection guide and it seems as though you should select a comonent that is rated slightly higher than the intended voltage, however other terms (Clamp voltage for example), I don't understand.

I was actually browsing the RS site looking at these :

ERZV07D241 metal oxide varistor,150Vrms

am I way off?

Reply to
ben

That's what I was thinking. Although it seems vaguely moot now. Actually US voltage is officially 120V btw.

RS is a pain. You have to log in even to look at data and I can't even remember our details now ! What's their problem ? Do they think someone's going to steal their website ?

Here's a couple of candidates from Farnell ( I've assumed 130V AC )

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Graham

Reply to
Pooh Bear

On Mon, 15 May 2006 21:06:25 GMT, "Ray L. Volts" put finger to keyboard and composed:

The "7" may indicate the MOV's diameter in mm. This in turn may be related to its joule rating.

- Franc Zabkar

--
Please remove one 'i' from my address when replying by email.
Reply to
Franc Zabkar

Note that the 240V mains supply is actually RMS - the peak voltage is nearer

320, which is slightly puzzling since quite a few manufacturers specify 275V varistors! Likewise, some switchable PSUs have 150V varistors across each of the 2 series connected reservoir caps - which often suffer from the failure of one VDR resulting in the destruction of the capacitor across the other VDR.

When I scrap a PC monitor, I always plunder it for any useful parts - and varistors definately fit this category, a certain Scandinavian made monitor had 1100V varistors in the mains filter circuit - they had a very vastly over optimistic view of the reliability of their SMPSUs!!!

Reply to
ian field

They normally specify by AC Volts. Hence no problem.

Graham

Reply to
Pooh Bear

Thanks again Graham (and others), I've ordered the new varistors from Farnel and will keep you posted.

One other thing was you asked abou the values on Q1 and Q2, they are :

Q1 K2972 Q2 C1741A

I can't see any damage to them, so we'll see.

Other thing that I forgot to mention. Right after it first blew, I swapped out the fuse for a correct version, expecting it to work OK (before I noticed the blown Varistor).

Plugging it in to the 110V supply though unexpectedly blew the fuse again - I say unexpectedly because if the Varistor was blown already at that point, shouldn't that have prevented a circuit to earth and a 2nd blow fuse, or am I missing something about the way Varistors work?

thanks again :-)

Reply to
ben

You might be missing the fact that overvolting the PSU has blown the chopper MOSFET S/C !!!!!

Reply to
ian field

remember

steal

2SK2972 - N-channel Mosfet - 500V 10A 40W ( looks like it may have survived then ! )
2SC1741 - NPN Bipolar transistor - 40V 0.5A 0.4W

Not sure to be honest. I hope it failed short. You could always measure its resistance now.

Hint - never replace a fuse before discovering why it blew.

Graham

Reply to
Pooh Bear

It wasn't a circuit to earth that blew the fuse, it was an overcurrent fault on the live / neutral circuit btw. Most faults don't involve the earth connection.

Graham

Reply to
Pooh Bear

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