The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

i have a superstar 250 amp everytime i hookup power it blows the fuse instantly what could be wrong its never been hooked up wrong

its a short some where..... did you check and make sure that nothing was over lapping or there is no burns or cut in any wires?

The power transistors could be blown, and internally shorting out.

there was no cuts in the wires and matter of fact it was working fine when i took it out and it just sat for a year or two and when i went to use it again it started blowing fuses its never been hooked up backwards that i know of which transistors should i replace and where could i get them would a electronics store where i buy caps,resistors,diodes,etc,have them or do i have to special order them do they have a reverse ploarity protection diode like cb,s have there is a big diode between where the positive and negative wires go to the board

Use the diode test function on your multimeter to measure the forward voltage across the diode. You should get around 500mV for it, if the diode is short then you will get a low reading. If it is shorted, then the linear has been connected in reverse without a fuse.

Download the datasheet for the output transistors and measure the forward voltage between the B and E, and the B and C. You should get similar readings, around 500-700mV. To test them properly you may have to remove them from the circuit, due to other components. One way round you should get an off scale reading (i.e. open) and the correct way round you should get the ~500mV reading.

Finding somewhere to get RF power transistors can be difficult, and sometimes it will be cheaper to buy a new linear amplifier rather than replace all of the transistors. If something else is wrong or you make a mistake it can get quite expensive and fill your bin with duff components