phase linear 400 voltages change

[laatsch55]

That's not what I mean Chang. A transistor can check good and still have no gain. It must have gain to do it's job. Solder the transistor back in, solder a jumper between the emitter and collector ( the outside leads) leave the middle lead alone. Then check bias when the amp is on...

 

[changdangnz]

Lee , I just want to double check. Resodering Q6 back to back wall chassis. On the leg just make a jumper cable between 2 lead out side then check bias current ?

 

[laatsch55]

Yes, but solder all 3 leads back in on the board from the transistor. Shorting the collector to the emitter tells you if Q6 is working or not. If the bias is close to zero then the rest of the bias circuit is OK and it is a lack of gain on the 3403 that is the problem.

 

[changdangnz]

Lee , I had been check q6 transistor and value is zero.but bias is still can not adjust .

 

[changdangnz]

Do I need to replace r20 ....?????

 

[changdangnz]

I also check so far a left channel meter is not moving as well . Something going wrong with a left channel .

 

[laatsch55]

If value is zero, then replace Q6, it is weak and has no to little gain.

 

[laatsch55]

I also check so far a left channel meter is not moving as well . Something going wrong with a left channel .

Is the left channel the one you are working on??

 

[laatsch55]

Chang, the jumper has to be on the emitter and collector, I told you wrong on the two outside wires. Jumper between the brown and red wires, the black is the base lead.

 

[changdangnz]

Yes , lee I was doing on left channel. I check a Q6 and it is weak value on it almost zero. I will go to buy this and replace it. Also I need to fix a meter on my left channel because meter not moving.

 

[laatsch55]

Chang, you can replace the 2N3403 with the 2N5088. You will have to pry apart the P-strap apart just a wee bit and drive the old transistor out. Clean the old epoxy out and insert the 5088 in. Be sure and check which way you want the hold down hole facing. Clamp together with a short 4-40 bolt and add a drop of epoxy on the non-lead side. The pinout on the 3403 is different than on the 5088 so check the data sheets so you can get the correct wire color on the correct lead...

 

[Northwinds]

Just thought I would check in this thread and see how your making out Chang

 

[changdangnz]

Not too bad. I fix an issue with bias and sold that amplifier already. Cheap price on Australia market . ( preamplifier 2000 , power amplifier 400 just $340 US ) . Now I need to go next step and fix my blow amplifier . Which option is the best ? WHITE OAK backplate and board or refurbish ?