Orion 280 gx

[mike49504]

Im working on this amp and missing a couple parts off the board when it was brought to me.

In the pic is the 2 parts that are missing wondering if anyone knows what part number belongs there?

[Perry Babin]

They are the same as the adjacent power transistor.

[mike49504]

the first 7 fets on each side are 2n6488's then the 2 blank spots

im stupid today what goes there? the 6488's? or6491's?

or 56's or 06's?

[Perry Babin]

2N6488s. Each channel has three 6488s and three 6491s (connected to the emitter resistors). The supply has eleven 6488s.

[mike49504]

Ok put the parts in this amp to test it and now it will play clean audio for 2 secs then make a loud squealing sound on the outputs and send out 14.86 volts on left channel and 11.87 volts on right channel

wondering where to go from here

[Perry Babin]

With no RCAs plugged in and the black probe on the main ground wire, do you read any DC voltage on the RCA shields?

If you don't at first, move the transformer a bit to see if it makes a difference.

[mike49504]

it starts at 0 volts on the rca shields if i try and move the transformer around
thats when i get 13.60 volts on the rca shields.

[Perry Babin]

The transformer is intermittently shorted.

Do you have a 2 ohm current limiting resistor?

[mike49504]

all i have right now is a 1ohm 10 watt resistor or that 2.2 ohm 2 watt resistor

[Perry Babin]

Use the 2 ohm resistor but watch it's temperature so it doesn't burn out.

Disconnect everything from the amp and connect the 2.2 ohm resistor between the B+ wire of the supply and the red wire on the amp.

Connect the power supply ground (from the 12v power supply) to either the RCA shield or the small black wire (if it has one) that's connected to the secondary center tap of the transformer. Dim the lights on the work bench and twist the power transformer. It should intermittently draw current from the power supply. When it transitions from drawing current to not drawing current, you should be able to see a spark between the windings that are intermittently shorted. Keep twisting until you can pinpoint the area where it's shorted.