Power supply for little halogen light popped

[bushtech]

This light stopped working when I switched it on.

Here is the little power supply:


On checking the 2 big 13005 transistors are shorted between all legs. Bit surprised by this as they are hefty jobs and show no signs of damage.

Also the diode D5 is open. It's marked DB3 and C53 as far as I can tell. Could it be this guy:?
https://datasheet4u.com/datasheet-pdf/STMicroelectronics/DB3/pdf.php?id=193115

240V in and AC 12V/40kHz out. Input current 185mA Power 50W max
The 4 Bridge rectifier diodes are good
What else needs to be checked.I don't know what the heatshrinked device bottom right is, so don't know how to check it. It measures 1.5MΩ
What else needs to be checked or can I just replace the transistors and the diode?

Many thanks for the help

 

[Tha fios agaibh]

I think that's it Bushtech.
You could check cap values or any resistor inline with the open diac/shorted Transistors.

What puzzles me is the heat shrink component. It looks like an inductor but should only measure about 0-50 ohms?

Is it in series with incoming power leads like a choke?

 

[bertus]

Hello,

Perhaps the info on this page might help:
http://sound-au.com/lamps/elect-trans.html
https://320volt.com/en/electronic-transformer-circuit-schematics-12v-halogen-lamp/

Bertus

 

[bushtech]

@Tha fios agaibh

Thank you. The mystery object connected to live line and other end to one leg of blue MOV and one leg of one of the br diodes.
Will check inline caps and resistors

 

[bushtech]

@bertus

Thank you for those very informative links. Busy wading through them

 

[bushtech]

If I am identifying diode D5 correctly it is a trigger diode with a fixed voltage reference. Have not been able to find a datasheet that shows it's internal layout but symbols of it show 2 diodes with the cathodes connected. No idea how you test something like this with a meter. Am I right that you can only test this item when it's powered up?

 

[bertus]

Hello,

In many of the schematics in the link I gave, the DB3 is mentioned.
This is a DIAC for triggering.

Bertus

 

[bushtech]

Yes thanks Bertus, I think it's identified correctly.

But the questions remain

 

[Tha fios agaibh]

I never checked a diac but you should be able to use variable power supply across it with a volt meter (parallel) to it, and increase voltage until the breakover voltage triggers at 32v. When it conducts voltage meter will drop. Of course you will need to either limit current by either adding a load/ resistor or using internal current limiting of a variable power supply. Otherwise its a direct short.

It's very likely your (looks like) "open circuit" diode (diac) is ok.

 

[73's de Edd]

Sir bushtech . . . . .

I must have accumulated upwards of a dozen different units of that family and am now starting to tear them down for analysis and parts . . .particularly / MAINLY for their 13005 thru 9 series of fast switching HV power transistors.
And yes they COMMONLY fail shorted, just like your encounter.
The heat shrinked MYSTERY unit is MOST likely a fusible resistor rather than being a micro pigtail fuse . . .with my finding most of them being of an average of 0.47 ohms.
Cutting away the shrink should reveal it as being a resistor.
Your shorted 13007's should have thoroughly taken it out.
The circuitry designs adjunct parts only mildly taxes the diac, so I suspicion it as still being good.
Your DB3 diac data sheet shows how to jury rig up a test jig for it, from loose discrete components from the bench.

73's de Edd . . . . .

From an early age, I could almost sense that my parents hated me.
My earliest remembrance of my first bath toys were a toaster and a plug in AC-DC radio.

.

 

[bushtech]

@Tha fios agaibh : Yes, I am going to call the diac good. In any case, my audioguru power supply only goes to to 30V, so that settles that

 

[73's de Edd]

Piggy back one, two or three 9V, series wired , inter plugged transistor radio batteries with one lab supply power lead and then, as if by magic, you will find yourself having a quasi adjustable stacked 9-39 volt or 18 -48 or 27-57 VDC supply !

 

[bushtech]

Ah, 73's de Edd to the rescue. Thank you for giving me the value of that fusible resistor. At a coupla million ohms as compared to 0.47ohms I think I can safely call it blown

So replacing the 13005's and the fusible resistor should sort this power supply.Will be ordering these parts.

Please can you have a look at this link: https://www.mantech.co.za/Stock.aspx?Query=13005and
My pick would be Fairchild one at top of list but I always battle with selection due to a lack of knowledge/experience.

Please tell me what I should go for

Thank you

 

[bushtech]

@73's de Edd: Brilliant suggestion thanks. If I get those parts and they don't sort the problem this will be the next thing I try

 

[bushtech]

The smallest fusible resistor Mantech has is 4.7Ω 1/4W. Can I stick ten of them in parallel?

 

[bushtech]

I stripped the heatshrink off the fusible resistor.

This is what I found:


Uhm. What is the value here? 5 band resistor. Neither white or red is a tolerance. The colours as I see it are red/black/silver/gold/white.

 

[73's de Edd]

Sir bushtech . . . . .meister

Either of power transistors options would be fine, as I am expecting that Fairchild unit to be coming from their Korean facilities.
(K prefix)

Can I stick ten of them in parallel?
ONLY if you want the current trip to be altered up to foil trace vaporizing level of ~ 10 amps


Now . . . . you can see the resistor better with it in your hand but to my perceived vision, from the HD monitor that is viewed on, as a BROWN for first digit,
( confirm on your monitors color reproduction----then eyebal the resistor ). . . . . . . .so you either have yourself a 1 or 2 ohm unit 1/4 watt . . . . . confusible resistor . . . . . in this case.
With that higher value of resistor, that unit is not not pulling as much power as other units I have encountered, but I have also seen 4.7 and up to 10 ohms used on lower power 60W and 15 watt lamps.

As you can see of the body of the unit, there was no color altering heat build up for the resistor . . . .it just went pffffffffffffffffffffftttttt in 764 milliseconds.

73's de Edd . . . . .

Statistically, 6 out of 7 dwarves are not Happy.

.

 

[Martaine2005]

I see Brown, Black, Gold, Gold and Grey!.
But I am that 1% happy dwarf with tired eyes...

Martin

 

[bertus]

Hello,

It is an 1 Ohms resistor.
Only the last white band I can not place.



Bertus

 

[bushtech]

Thank you all very much.
I would never doubt St Edd so 1 or 2Ω 1/4W it will be.
It seems to be very difficult to find fusible resistors here. Found some 0.47ohm 1/4 W at RS but not likely to buy 4000 of them.

Can I not shoehorn a 1 or 2ohm resistor in there in series with a suitably rated fuse. Spec of fuse to be determined. The halogen globe it drives is 20W.
Or is there a more elegant solution?