Phase Linear 400 issue help!

[laatsch55]

There's the temp difference though. 465 is way high. Try some de-oxit on the pots. With the amp off de-oxit the pot and wirk it about 50 times.

 

[enoyes12]

I don't think the PS caps were completely discharged its dropped to 400mV left 100mV right

 

[laatsch55]

Does it have the open type pot?

 

[enoyes12]

orange finger turn type I think original

 

[laatsch55]

To check the pot, put one lead on the center lead and one on the side lead and actuate the pot and watch the resistance, it's a 5K pot. Then switch to the other outside lead and do the same.

 

[Gepetto]

To check the pot, put one lead on the center lead and one on the side lead and actuate the pot and watch the resistance, it's a 5K pot. Then switch to the other outside lead and do the same.

Those cheap pots are notorious for just failing outright...

 

[enoyes12]

after cleaning on one side I get 0k-5k and nothing on the other side on both pots. they where dirty. but still no change on the bias adjusting them

 

[enoyes12]

let me clarify that I get 0.00 on the other side

 

[enoyes12]

Looking at the back side of the board 2 of the connections on the pot are connected by a trace that side is showing the short. The pot seems to work with the meter but im getting no change in the bias. It doesn't make sense, I should get some change if the pot is working right?

 

[laatsch55]

Unless the bias transistors are some tired ol 3403's. Yes the middle and one outside lead on the pot are on the same trace. Check R19, should be a a 470 ohm resistor. See how close it is.

 

[enoyes12]

468k

 

[enoyes12]

now that the PS caps are fully discharged I think, its showing .280 left and .080 right.

 

[laatsch55]

468 K ??

 

[enoyes12]

.468k sorry my fat fingers missed the period

 

[Gepetto]

.468k sorry my fat fingers missed the period

Do the chassis mounted Q6 transistors check OK as NPN transistors?

 

[enoyes12]

huh. you just talked right over my head. NPN transistors?

 

[Northwinds]

huh. you just talked right over my head. NPN transistors?

If it conducts with the base positive, the transistor is NPN

If it conducts with the emitter positive, the transistor is a PNP

 

[enoyes12]

OK, pretend your talking to a dummy and I'll see if I can keep up. Where are the transistors, I see them on the schematic but where are they in the case?

 

[Gepetto]

OK, pretend your talking to a dummy and I'll see if I can keep up. Where are the transistors, I see them on the schematic but where are they in the case?

See what you get on the 3 wires going to the back middle of the board. Brown is emitter, black is base and red is collector.

 

[Gepetto]

See what you get on the 3 wires going to the back middle of the board. Brown is emitter, black is base and red is collector.

Those are the wires you showed in your earlier pictures. 2 sets of 3 wires right in the middle of the mold/spore patch