phase linear 400 voltages change

[laatsch55]

Amen....my 170 won't go below 10 nf.

 

[laatsch55]

179...

 

[changdangnz]

Lee, i wondering want to ask you to measurement bias transistor is that power on or off ? On 400c i cant find Q3 can you tell me where is it ?

 

[NavLinear]

Lee, i wondering want to ask you to measurement bias transistor is that power on or off ? On 400c i cant find Q3 can you tell me where is it ?

Chang,

The service manual has a procedure for adjusting bias for the 400C board - this is done with the power on. The PL 400 with the 400C board has Q3 located on the chassis (compensates for temperature) with three wires attached to the legs of the transistor (one for each channel) going to the control (400C) board.

 

[changdangnz]

Many thank navlinear. I had been rip off by service man. 50 buck gone for checking and he said not available to fix it. What is a waste my time

 

[NavLinear]

Many thank navlinear. I had been rip off by service man. 50 buck gone for checking and he said not available to fix it. What is a waste my time

I may be wrong with the location of the bias transistor. I reread this thread and it seems that there is a possibility that the bias transistor is on the board. You'll need to look at the control board and if you can get some photos of it and the back chassis wall. That would help to nail this down.

 

[laatsch55]

The pics you have posted so far Chang, the bias transistor is Q6 and located on the back wall. There is a difference between CHECKING the bias transistor and CHECKING THE BIAS CURRENT. What do you want to check?

Any Phase Linear amp can be fixed. The 300 Series II requires outputs that are no longer available but that's probably the only one.

PL's can be difficult at times because when something bad happens there can be a lot of collateral damage that is difficult to track down, and as your knowledge of the amps general design DECREASES, the difficulty INCREASES.....

Chang, are you going through a translation program, or are you communicating through a rudimentary understanding of English?

 

[changdangnz]

I want to adjust bias on Pl400c PCB . I'm using my little knowlege of English to read through all instruction service manual. When I measure R24 and R41 a power is off and value is not between 300-400 mV . That is why I just want to ask you about it.Lee what do you mean CHECKING BIAS CURRENT ?

 

[changdangnz]

lee , did you have any power tranformer for PL400 on dual primary voltage ? i want to updrade my PL400 blow fuse line to WOPL . ALSO I Need to change a voltage for a new PL400 I just bought to 220v . I hardly to find anyone have a power transformers PL400 dua, primary voltage sale on eBay.

 

[laatsch55]

I want to adjust bias on Pl400c PCB . I'm using my little knowlege of English to read through all instruction service manual. When I measure R24 and R41 a power is off and value is not between 300-400 mV . That is why I just want to ask you about it.Lee what do you mean CHECKING BIAS CURRENT ?

To check bias current, you have to put your meter leads on each side of the 10 ohm resistor on the first row of transistors on the backwall from the transformer end. Put your meter on DC volts. Amp must be on, you need a reading between 350-380 millivolts...



When we measure the bias current we are really measuring the voltage drop accross that 10 ohm resistor. Hook up your meter and post a pic.

 

[laatsch55]

lee , did you have any power tranformer for PL400 on dual primary voltage ? i want to updrade my PL400 blow fuse line to WOPL . ALSO I Need to change a voltage for a new PL400 I just bought to 220v . I hardly to find anyone have a power transformers PL400 dua, primary voltage sale on eBay.

I don't have any...and they are hard to find...

 

[changdangnz]

lee , i just measure a R24 and R41 on PL400C . It is quite hight value than expect on service manual. I got R24 is 517mV and R49 is 538mV . Do i need to adjust back to 300mv or 400mv ????

 

[changdangnz]

i adjust bias to 350mv . thank you Lee

 

[laatsch55]

Good Job Chang. The bias needs to be adjusted to the measurement of the positive drive transistors, meaning the 1st and 3rd rows from the transformer...

 

[changdangnz]

Lee , this morning when I play my PL400 PCB 14a . Left channel is very low and noise. I check up bias and left channel is 634 mV and left channel is good 380 mV. I try to adjust left channel on R20 to get 380 but it's not even change . What can I do for it lee ?

 

[laatsch55]

The bias transistor Q6, has probably lost gain over the years and is no longer effective...

 

[changdangnz]

I see , Lee is that the transistor been mount on back wall ? I will replace it.

 

[laatsch55]

Yes it is Chang....

 

[laatsch55]

Chang, that is not all it can be, but that's where I would start.

Unsolder the bias transistor from the board and perform the transistor checks on it...Sometimes when an output blows it can stress the bias transistor...

 

[changdangnz]

Lee , you are right . I unsold a q6 and check I . It is fine. I will need to check a bias out put .