Bush BFSAT01HD problem

[bjeans]

Where can I find out what transistors are used in the Bush BFSAT01HD, I have a blown LNB switching transistor and it just says AG QA on the top.
Regards Brian

 

[satelliteman]

That's a fairly new receiver so a schematic diagram may not be readily available.

 

[bjeans]

Argos will not help becuase it is just out of warranty and Bush say 'it is not repairable - no spares are available', they suggest I buy a new one.
For the sake of one transistor in location Q7 I can not belive that a 13 month old HD Freesat is unrepairable !!

 

[Llew]

Welcome to the forum.

It's a general purpose NPN transistor, surface mounting SOT23 (SMD). BCX70G.

_http://www.classiccmp.org/rtellason/transdata/bcx70g.pdf

 

[Llew]

If you're confident replacing the transistor yourself, you can obtain one from Farnell's (_http://uk.farnell.com) and enter BCX70G in the search box.

 

[bjeans]

That was great news - thanks.
Both Bush and Argos had told me it was not repairable, but that is the only transistor that has blown and there was no voltage going to the LNB.

 

[PaulR]

Do you know why the transistor blew? It may be that it'll blow again when replaced.

 

[Lazarus]

Thermal runaway due to insufficient ventilation around the box, I shouldn't wonder.

Egg Fryers, those boxes.

 

[satelliteman]

More like cheap semi conductors.

 

[Llew]

...or lack of any protection for short circuits in the LNB supply.

 

[mikeswann]

good day! i have one of these boxes and i was having all sorts of problems with the sound and picture but found out it is the HD out put, no warranty suport forthe box. the over heating was bad so i cut away the top and stuck a computer fan on top so it was cold al the time this helped but still the sound and picture fails. if i run it though the scart socket its fine but the picture is realy bad.

if you stil need a chip mine is working just not the HD out, i would be willing to part withit for half the buying cost of 30 pounds plus postage. letme know by email

thanks
mike

 

[satelliteman]

Any negotiations must be posted in the thread and not by PM/email, as per the section rules.

 

[bjeans]

I have done some more investigation and Q7 is not a transistor but a voltage regulator. It appears that this is the item that switches between the two voltages and is surface mounted, it has two markings on the top - AG and QT, and has got 3 contacts on one side and what appears to be a heatsink on the other.

I still don't know what to replace it with !!

Any more ideas?

 

[bjeans]

Q7 in a BFSAT01HD is a voltage regulator for LNB voltages.
Any ideas what type it is ?

 

[Llew]

Well I was going on the information you gave. AG is a transistor, a QT marking would suggest an optoelectronics device (QT Optoelectronics). Not what you're looking for. More research needed, unless someone can pinpoint the item.

 

[bjeans]

Thanks for all your input, I have just been taliking to somebody else who says that it is AG and QT on the chip, but he thinks it is a SOT89 package ?

 

[Llew]

If it's a 3-pin voltage regulator, they're usually fixed voltage devices, with the common (ground) switched to 13/18V by the microprocessor.

For instance, I have a receiver which uses a 12V regulator for the LNB output (not an SMD type) with a 21V supply on the input pin, and the normally 12V output raised to 13V or 18V by raising the ground pin by 1V (vertical switching) or 6V (horizontal switching), switched with these voltages by an input line from the processor.

Looks like an SOT89 regulator has the centre of the three pins as the ground terminal, connected internally to the heatsink, and the output as pin 1 and input pin 3. Whether it's a 12V regulator you have, I wouldn't know.