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Help on blown transistor please

Spike

Feb 7, 2012
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I have a transistor with a pinprick hole ( in red circle on photo "Board") which I need help in identifying. The transistor is 2.8mm x 1.3mm. It's driving an indicator bulb with 28 volts from the rectification section adjacent to where it says "Solder Side". The control side of the transistor comes from pin 4 (I think it's pin 4 - there's no dimple or mark) of the HEF4724BT 8 bit addressable latch marked with a red dot. The actual transistor is in the photo marked Blown Transistor. There's no identifiable marks on the transistor.

So can someone help with identifying the transistor please, so I can get a replacement?
Also, what sort of indicator bulb would it be, running on 28 volts? The old one, which I don't have any more, looked like an LED but it can't be at 28 volts, and there was no visible resistor. Thanks.

As an edit, I would add that the manufacturer has no knowledge or recollection of this board. I don't know how that can happen, but there we are.
 

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davenn

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Sep 5, 2009
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As an edit, I would add that the manufacturer has no knowledge or recollection of this board. I don't know how that can happen, but there we are.

without knowing what the board is, what it is from ... make and model ... who knows

what efforts have you made to fins a schematic ? contacting the manufacturer etc ??
 

Spike

Feb 7, 2012
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The board is from a 1992 Genvex 525VP heat recovery unit. I have sent Genvex in Denmark photos of the board and they claim no knowledge of the board. There's no board manufacturer name on the board. I haven't been able to find any board schematics, only the connection diagram.

Of course, I realise Genvex want me to spend £11,000 on a new unit, but I'm reluctant to do that when my existing unit is basically OK.
 
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CircuitMaster

Dec 17, 2016
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Its very hard to tell from the dust thats left. But given the "28VDC", you can try replacing it with 2n3055 if its an NPN transistor or 2n2955 for PNP.

MOD EDIT: I urge people to consider posts by CircuitMaster with a HUGE grain of salt before ignoring them.
 
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73's de Edd

Aug 21, 2015
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Sir " Spike " . . . . . . .

Use of a 2955 or 3055 as a sub in THIS transistors SPECIFIC function would be akin to the setting in of a CORVETTE engine into a go kart.

Need a good photo (LARGER ) of the OTHER side of the board that the foil side is now presented .
You did not have a DOT- - - white/silver bar- - - or U cut out index at the end of that HEF4724B for #1 pin index referencing ?
Its pins 4 or 5 or 13 would all be valid outputs to follow the BLUE arrow line over to the BLOWN driver transistor.
If the other side of the board could be seen, the foil paths of the different power and grounds could be differentiated and established.

Need to see the part number markups at the left, for the 18 pin IC RED unit, as it certainly seems to be a u/p with a mini separate 8 pin EAROM (YELLOW STAR) . . . .. located at the bottom of the unit. for its program memory. . .
Need the YELLOW and RED transistors also.
PLUS , am I correct that your marked in BLUE + and - at the very bottom corner, connect to the lamp ?
Also, are all functions of the unit being operational, with the exception of just this lamp not lighting up ?

Wouldn't hurt to give the other numbers on the 4 other support IC's just above the multiplexer.

ADDITIONAL BOARD MARKUP . . . .


pKFyw48.jpg



73's de Edd . . . . .
. . . . . . . . . . .


Five out of four people have trouble with fractions.
 
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BobK

Jan 5, 2010
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If all it is doing is running an indicator, replace it with an LED and any general purpose NPN will do. In fact, if you use a high brightness LED you might be able to drive it directly from the output.

Bob
 

Spike

Feb 7, 2012
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Feb 7, 2012
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Thanks 73's de Edd for that reply - you have given me a clue that helped me solve the question of what the transistor is. I do have a further problem with this board, the details of which I will post shortly.
 
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