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[chrisio]

I know there are some exceedingly clever people on here so here goes.

The power supply for my laser machine went pop in a rather spectacular fashion and it looks as though the fusible link went pop.

I have a new power supply on route however I want to see if it was just a fluke that made it go bang or if its terminal.  can I replace that fuse and try again and if so what with.  I can't find anything online that resembles what it once was.

The rebel in me says just link it out with a bit of copper wire but seeing how the thing went pop I rather dread the consequences of my actions if I did that.  I also realise that its probably a hiding to nowhere but you never know and if it holds then I have a spare power supply for the future.

I have uploaded some pictures for you to have a look at.

Overview

Link to full size image
https://www.penrithposters.co.uk/new/wp-content/uploads/2016/08/20160803_093042.jpg

Fuse

Link to full size image
https://www.penrithposters.co.uk/new/wp-content/uploads/2016/08/20160803_093051.jpg

Thanks in advance.

Chris

[aaronjb]

Axial leaded tube fuse: http://www.optifuse.com/fuses-tube.php

Given the spectacular fashion that fuse detonated itself, though, you might want to start looking for dead shorts first - depending on where that fuse is either on the input or output side of the PSU; physical location implies output so perhaps the load has gone dead-short?

[LFF64]

You need to find the cause of the fuse going other wise you are going to end up with another dead psu

[chrisio]

Thanks both of you. 


The output side of things does make some sense as I was aligning the lenses  and tube and managed to trap one of the tube wires (not the high voltage lead) without noticing.  It was running fine like this and only went pop after moving this wire.  I will double check the insulation on the wire and go from there.

Chris

[Bigron]

I would agree with the above, but it's also worth checking the diodes in the top left hand corner; a short circuit in any of those will detonate your fuse!
Of course, there are other power components that could be suspect, but you have to start somewhere.....

Ron.

[TheBoy]

Looks smps to me, so needs a specialist - cant just go looking for short, by their nature many will show a short even when working.

[Bigron]

Yes, definitely switch-mode, TB, which is why I suggested checking those four input bridge diodes - a most common cause of fuse anihilation!
I also concur with you that apart from that simple check, SMPSs are not an easy fix! However, it will cost nothing and hurt nobody to check any power semiconductors for short circuits because they are under the greatest electrical stress and fail often, especially if they are lightly or under-rated for the job, for reasons of economy.....

Ron

[chrisio]

Whoooosh!

Most of all of that went over my head to be honest.  I can poke about with a multi meter and wield a soldering iron with the best of them but when it comes to understanding what the multi meter is telling me I don't really have a clue.  With the diodes I take it I can set the meter to continuity and see if I get continuity one way but not the other?

I don't really fancy poking about too much as there is the laser coil at the top of the board and that is in high KV ranges and I bet it would make my hair stand on end if the meter leads ended up in the wrong place!.

I haven't had a chance to look at it today but I would hazard a guess and say that I managed to short the cable out that is in the location of the laser tube because if what aaronjb surmises is correct about that fuse being on the output side of  things it would make sense for it to blow when I caught this lead.

I shall have a check tomorrow.

All the best
Chris

[Steve B]

just replace that fuse and then just power up with some rubber marigolds on and see what happens 

[chrisio]

I certainly am tempted and lets face it, it went once so if the fault is still present it will go pop again.

[zirk]

Whoooosh!

Most of all of that went over my head to be honest.  I can poke about with a multi meter and wield a soldering iron with the best of them but when it comes to understanding what the multi meter is telling me I don't really have a clue.  With the diodes I take it I can set the meter to continuity and see if I get continuity one way but not the other?

I don't really fancy poking about too much as there is the laser coil at the top of the board and that is in high KV ranges and I bet it would make my hair stand on end if the meter leads ended up in the wrong place!.

I haven't had a chance to look at it today but I would hazard a guess and say that I managed to short the cable out that is in the location of the laser tube because if what aaronjb surmises is correct about that fuse being on the output side of  things it would make sense for it to blow when I caught this lead.

I shall have a check tomorrow.

All the best
Chris

You cant really test diodes or transistors using continuity test whilst there still pcb mounted, best way is to lift one of the legs, but yes as you say with a diode in your hand switch the DVM to diode symbol test and measure both ways, in the old days with an Avo 8 on the bench you would use resistive test bearing in mind the negative lead on the meter would actually be positive in order to read forward current flow. 

if it was me, and I know I had definitely caused a short which then blew the fuse, I would replace the fuse and switch it back and see whats occurring, but thats me, just dont burn the house or garage down. 

[Rods2]

Whoooosh!

Most of all of that went over my head to be honest.  I can poke about with a multi meter and wield a soldering iron with the best of them but when it comes to understanding what the multi meter is telling me I don't really have a clue.  With the diodes I take it I can set the meter to continuity and see if I get continuity one way but not the other?

I don't really fancy poking about too much as there is the laser coil at the top of the board and that is in high KV ranges and I bet it would make my hair stand on end if the meter leads ended up in the wrong place!.

I haven't had a chance to look at it today but I would hazard a guess and say that I managed to short the cable out that is in the location of the laser tube because if what aaronjb surmises is correct about that fuse being on the output side of  things it would make sense for it to blow when I caught this lead.

I shall have a check tomorrow.

All the best
Chris

You cant really test diodes or transistors using continuity test whilst there still pcb mounted, best way is to lift one of the legs, but yes as you say with a diode in your hand switch the DVM to diode symbol test and measure both ways, in the old days with an Avo 8 on the bench you would use resistive test bearing in mind the negative lead on the meter would actually be positive in order to read forward current flow. 

if it was me, and I know I had definitely caused a short which then blew the fuse, I would replace the fuse and switch it back and see whats occurring, but thats me, just dont burn the house or garage down. 

Those were the days! Big MK8 Avo with bakelite case, mirror parallax and current cutout* and apprentices being apprentices! More challenged apprentices and winding a transformer, then doing open and circuit tests. Winding the short circuit test rheostat down and an elbow on the Avo *reset button measuring current, created muh satisfying smoke as you timely walked away for our line management turning up to it sort out! Not that I was ever involved in such terrible apprentice acts or worse of course.

[Bigron]

Slightly off-topic, Rods2, but in line with your comment - do you remember how much a revered Avo 8 cost back then, compared to a far more capable DMM of more recent times? Eye-popping price, yes?

Ron.

[Marks DTM Calib]

The most likely failure will be one of the those rectifier diodes top left, you can test those quite happily whilst still fitted.

[Bigron]

"Marks", I've said that twice already - see above! 

Ron.