SIP Ideal 120 Blowing panel fuse

[mike 109444]

Licker with what you have checked so far (by disconnection) and the fact that the fuse is only 5amp and is probley only there to disconnect power to the pcb in the event of a fault I would be suspecting the pcb. The pic of pcb looks ok ie no signs of fried components. There are 3? transistors at the far end of your pic of pcb and one of them being dead short would blow a 5amp fuse without looking fried. Can you note the markings on the transistors. It might also be worth looking through the wiring for any wires that might be pinched or shorting. The fact that you have been going through most of the wiring it would be more likley pinched. Check where wires go through unprotected holes. Would have been nice to get a schmatic for pcb.

 

[Sean]

there are 2 diodes that look like they piggyback resistors above the midddle twiddly knob looks like there has been overheating there.

 

[Windy Miller]

there are 2 diodes that look like they piggyback resistors above the midddle twiddly knob looks like there has been overheating there.

I saw that too, but I don't think it's overheating. It looks more like the flux has run onto the pcb a little where the piggy back soldering was done. Not a very professional soldering job, and possibly not original - I wonder if this has been repaired at some point in the past?

 

[Licker]

OK, some better pics:

Are these the transistors that you referred to?

The diode / resistors:

And finally the back of the board:

If you could tell me how to test those components (I have a multimeter, but not much of a clue ) it would be appreciated. Will also check over the wiring again when I get home later.

Cheers

 

[mike 109444]

Licker thoes are the 3 devices I was refering to. They are SCR's and are not that easy to test while still in circuit. (would need to desolder to meter up, but even then no to easy to check with basic meter. They are not that expensive if they did need to be replaced. There are 2 more power (transistor type devices?) stood upright on the board. What are thoses?. The frount mounted fuse that keep blowing has 2 wires connected to it, Where do they come from/goto?

 

[the snooper]

we need to know what the fuse connects to and from, if the fuse operates at mains voltage then it wont be the pcb at fault.

with a new fuse in does the fan run ? if it is around 12 - 24 volts then it could be the board or wire feed motor

it wont be the welding rectifier No 8 that mike labelled, if they go the machine usually creates a violent buzzing noise

 

[mpranski]

the insulator in the torch (we call it a whip on this side of the pond) could be bad. I have had this happen to me before. It shorts out as soon as you pull the trigger. MVP

 

[Licker]

Good afternoon guys

Snooper: The fan runs OK, even with the fuse blown.

mpranski: I've taken the torch off and shorted across the 2 pins where the torch connects into the machine - I belive this would be the same as pulling the trigger, yes? The fuse still blows instantly.

Mike: The 2 wires from the fuse go directly onto the PCB. I've tried to sketch out the paths they take on the board in the pic below. This is not a complete diagram, because I tied myself in knots trying to figure it out. The numbered circles are supposed to represent components on the board that I don't know the names of, so the second pic is a key.

Cheers!

 

[the snooper]

it would probably be better just to indicate the 2 connections that the fuse conects to on the rear of the pcb

 

[Licker]

Hi,

The fuse connects to the board at the top left 2 connections.

Cheers

 

[the snooper]

chances are it could be the triac your number 7 although triacs just usually do nothing when they have gone or a diode your number 1,2,4,5

my money would be on one of the scr's tic116m

it would be worth checking the diodes they only pass power in one direction, some you can test on the board any which show up as suspect you must remove 1 connection

 

[the snooper]

here is a site that will explain how you can test the scr with a meter

 

[Licker]

Cool thanks. I have a diode check function on the multimeter.

8 diodes on the board, 4 give a reading with the probes both way round and 1 gives no reading at all. Would you suggest removing these 5 and testing out of the board?

Just tested those SCRs and all 3 give reading that indicate they are indeed not well

Looks like a Maplin/RS/Farnell order is about to be placed.

Thanks again for all your help

 

[dannyp]

unless a component is unavalible or expensive i never test them just replace all that chould be suspect

usual suspects i look for are

transistors, electrolytic capacitirs.

i would check big resistors like the wire wound in no11 the wire can farcture inside rare but dose happen easy to check tho

 

[the snooper]

i would remove at least one of the connections and try them again the one doesnt read at all is also worth removing but do remember that they must go back in as they came out remember or even draw which side the silver band is as putting them in the wrong way round would be a dead short on the board

as for the scr's they also behave like diodes for a simple test ie the gate and the cathode should only let current flow in 1 direction
however between the anode and cathode cureent should flow in either direction so using the meter you should be doing 4 tests per scr

 

[mike 109444]

Licker I would suspect one of the two components at the ends of the black lines in pic I assume they are both scr's? (one on heatsink is). It also loks like a dry joint on one of the solder-in wires. When you shop for the parts get your self a solder sucker as they make life (and removing components) much easer
You could do a comparision test by finding another component of the same type on the board, Desolder them both from the board and then meter the "sus" part and compair with "belived good" part and you may find a short with the "sus" part

 

[Licker]

Yes, one is an SCR and the other is a triac.

Have chucked an order together for various bits - surprised how cheap the stuff is - could probably replace most of the components for about £30 - so will have a go later in the week when they arrive. Also taken the advice about a solder sucker and even going to get a more precise soldering iron, as my 100w thing is a bit bulky

Have taken some good reference photos of the board so I don't cock up putting bits back the wrong way and with any luck, a following wind and the planets aligning correctly will see the thread marked a 'solved' by next weekend.

Thanks again everyone for your input, really appreciate you taking the time to help out an electronics-phobe