STAR TSP100 blown fuse

[Half-Saint]

I got a STAR TSP100 receipt printer which has blinkng red/green diodes. I took out the power supply and tested the fuse which turned out to be blown. It was one of those brown rectangular 3.15A 250V fuses often found in monitor power supplies. Five minutes later, a new (ROUND) fuse was soldered.. plug in USB.. blinking LEDs.. plug in power.. BANG, fuse blows. I did this twice just to make sure

Nothing looks burnt on the PCB and the caps look okay despite being Elite branded. I suspect a short circuit somewhere but where?

Cheers
SainT

P.S. There were a bunch of dead ants inside the PSU but not sure, if that could have caused it to die in the first place.

P.S.S. Can a 4A diode be used in place of a 3.15A? The PSU is rated 100-240V AC, 1.4A

EDIT: I tested the triac out of circuit (BTA12-8CWG https://cdn.badcaps-static.com/pdfs/...5f7a156230.pdf) with multimeter set to diode:
A1 > G : 0.056V
A2 > G : 0.056V

Resistance:
A1 > G: 74.7 ohm
A2 > G: 74.9 ohm

Continuity tester between A1 and A2 beeps.

EDIT #2: tested the thermistor and it checked out fine. Removed the wirewound resistor from the circuit and it reads 0.L. It also appears to be chipped on top and I can see a little bit of wire.

[japlytic]

Re: STAR TSP100 blown fuse

From the pictures, I can see that fuse FS1 is T3.15A - what does the "4A diode in place of a 3.15A" refer to?
Also check for shorts across the 400/450V capacitor; if there is a short, try removing power MOSFET Q1 (and the other TO-220 package device near the yellow AC capacitor) and check for shorts; also, check for shorted diodes.
I doubt that the bridge rectifier (a 4-terminal package) would be internally shorted, but this is possible.

[Half-Saint]

Re: STAR TSP100 blown fuse

I just wondered, if it would be possible to replace that T3.15A with a T4A fuse since I have only one T3.15A left and plenty of T4A :-)

All diodes that I could find (5) check out fine.

[stj]

Re: STAR TSP100 blown fuse

meter the resistance across the big cap while it's on the board.

[Half-Saint]

Re: STAR TSP100 blown fuse

meter the resistance across the big cap while it's on the board.

While in the board, it reads 7.5 ohm...

[budm]

Re: STAR TSP100 blown fuse

So what is the resistance reading between A1 and A2?
What is the resistance reading between S and D of Q1?

"Removed the wirewound resistor from the circuit and it reads 0.L. It also appears to be chipped on top and I can see a little bit of wire" Which resistor is that one? Ra1?

[Half-Saint]

Re: STAR TSP100 blown fuse

So what is the resistance reading between A1 and A2?
What is the resistance reading between S and D of Q1?

"Removed the wirewound resistor from the circuit and it reads 0.L. It also appears to be chipped on top and I can see a little bit of wire" Which resistor is that one? Ra1?

Resistance between A1 and A2 is 0 ohm.

I haven't desoldered Q1 so can't tell for sure but while in circuit it's 0.L.

The resistor you ask about is indeed Ra1.

[budm]

Re: STAR TSP100 blown fuse

Removed the wirewound resistor from the circuit and it reads 0.L.,Ra1 = bad.
This Ra1 looks to beconnected to the Source pin of the Q1, so for it to blow open circuit, Q1 may have shorted out between S ad D then blown open circuit.
Resistance between A1 and A2 is 0 ohm = bad

[momaka]

Re: STAR TSP100 blown fuse

Also, you can save your fuses from blowing if you put a incandescent light bulb in series with the power supply mains. Like this:
https://www.badcaps.net/forum/showpo...4&postcount=70
If the bulb stays fully lit, you still have a short somewhere.

You probably won't be able to test the power supply with the printer connected, though (since the incandescent light bulb will limit the power to the PSU).

[Half-Saint]

Re: STAR TSP100 blown fuse

So, if I understand correctly, I'll have to replace Ra1 (resistor), QT1 (triac) as well as Q1 (MOSFET)?

How do i find a replacement for the Ra1? Couldn't find anything online that would help be decode the color rings on this one.

[japlytic]

Re: STAR TSP100 blown fuse

So, if I understand correctly, I'll have to replace Ra1 (resistor), QT1 (triac) as well as Q1 (MOSFET)?

How do i find a replacement for the Ra1? Couldn't find anything online that would help be decode the color rings on this one.

Are you actually refering to resistor Rs1 (brown green silver gold)?
Also, what are the markings on TRIAC QT1 and MOSFET Q1?
With a multimeter, do you measure shorts between the pins of MOSFET Q1 when in-circuit (with power disconnected)?

[Half-Saint]

Re: STAR TSP100 blown fuse

Are you actually refering to resistor Rs1 (brown green silver gold)?
Also, what are the markings on TRIAC QT1 and MOSFET Q1?
With a multimeter, do you measure shorts between the pins of MOSFET Q1 when in-circuit (with power disconnected)?

Yes, sorry, that's Rs1 not Ra1. I don't know where I got Ra1 from :-)

QT1 triac is BTA12-8CWG and Q1 MOSFET is K4112. Q1 resistance measurement between S and D was done in-circuit while power was disconnected and the fuse is dead so not much difference...

[Half-Saint]

Re: STAR TSP100 blown fuse

Hey, still hoping to fix this beast, thanks :-)

[Half-Saint]

Re: STAR TSP100 blown fuse

The biggest question for me right now is how to figure out what kind of a resistor I need to replace the one that's broken?

After looking at the datasheet of BTA12 series triac also not sure which one to get.. I'm thinking 800V, 12A, 25mA but most of this is gibberish for me.

[budm]

Re: STAR TSP100 blown fuse

That resistor is 0.15 Ohms MOX (Metal Oxide) flame proof resistor. What is the dimension? It looks be about 1W.
From your post 'BTA12-8CWG'
Order code:
BTA12-800CWRG for Isolated Tab, 12A, 800V, CW = 35mA Gate drive current sensitivity, snubberless, package style TO-220AB.
See page 7/12

[Half-Saint]

Re: STAR TSP100 blown fuse

Thanks for the input, budm.

The resistor is approximately 10mm x 4mm.

[budm]

Re: STAR TSP100 blown fuse

So it is about 1W resistor.

[Half-Saint]

Re: STAR TSP100 blown fuse

OK, parts arrived today and I replaced the resistor, triac, mosfet and a new fuse which got blown again.

Anything else I can look at before giving up?

EDIT: just noticed the thermistor 10s2r5m has a very small burn mark so I desoldered it and it measures 3.4ohm out of circuit. Should be 2.5ohm at 24C. Not sure, if this is still okay or not. It wouldn't be possible for the burn mark to come from anything else.

[momaka]

Re: STAR TSP100 blown fuse

I'll try one more time
https://www.badcaps.net/forum/showpo...36&postcount=9

This will save you lots of fuses. Also, you can try removing components until the short circuit is gone.