So, here I go. Phase Linear 400

[laatsch55]

In pic #6, the output on the left, is the output hold down screw touching the bus bar?

 

[VSAT88]

Done with the cleaning and it looks nice. I have checked all of the buss bars and no screws are touching.

 

[laatsch55]

Bring it up one more time, on the DBT, and variac and see how much rail voltage you can get and recheck Offset....

 

[fitz43]

 

[Northwinds]

View attachment 30225

That is a very crispy pretzel stick indeed!

 

[VSAT88]

Measuring from the left speaker terminal to chassis 33.8 DC rail voltage. Measuring from the right speaker terminal to chassis - 33.4 DC rail voltage. DC offset on the left speaker wires/terminal it is showing 30.4 volts DC. DC offset on the right speaker wires/terminal it is showing 25 volts DC. Across the main filter caps I have around 28 V DC before the left meter starts pegging out.

I have a lot to learn. When I was measuring DC offset before I totally forgot that when I disconnected the speaker protection board I also by default disconnected the wires to the speaker terminals. I am now actually measuring at the speaker wires that I taped off before. Sorry, my bad. I hope I am measuring rail voltage the right way, from chassis to each speaker wire at the fuse.

As far as pretzel sticks there are more than one. There are five of them.

 

[laatsch55]

Rail voltage is plus/minus DC coming off the filter caps. When you measure across the speaker wires that is DC offset voltage. When you measured DC offset, was it plus or minus DC?

 

[laatsch55]

So....you have mica AND sil-pads under each output transistor?? From your first post that's what it sounds like. I'm guessing that your large DC offset is a minus voltage reading, AND beins you dismounted and remounted all outputs I'm guessing you have continuity between an output case and the chassis. Put the negative lead on chassis ground and check the case of each output transistor and see what ya get.

 

[VSAT88]

Said I was a noob but not that much of a noob. No sili-pads and mica, just mica with wakefield on both side for heat transfer. I will do what you said and be right back. Thanks.

 

[VSAT88]

On both speaker wires the offset measurment was +. Measuring rail voltage with the negative probe on the buss across the filter caps and the + probe on the top filter cap (other side) the voltage was +31 v . The bottom filter cap reads -21 v then when the meter on the left starts pegging out the voltage starts jumping between 14 v and 21 v . All measurment made were at 100 vac on the veriac.

On the other post you told me to measure from chassis to each output transistor. I hope you meant continuity. The meter does not sound for continuity to any of the transistors. No direct shorts there.

 

[VSAT88]

I checked the bridge rectifier and I have continuity to every lug to ground. That does not seem right to me. I checked and in every direction on the four lugs they also have continuity to each other no matter where the probes are placed. Is that right ?

 

[Netfly]

Try setting your meter to a lower scale. Like 100 or 200Ω.

 

[VSAT88]

Try setting your meter to a lower scale. Like 100 or 200Ω.

I set the scale to 200 Ohm and got .004 from both the AC sides of the BR to chassis ground. .458 on the negative DC side. On the DC + side of the BR we start at around the same, .500 or so and it steadily climbs up till it goes off scale.

 

[Netfly]

With the power off. Measure each diode in the BR separately. Across the one diode, not to ground. Each should show some resistance in one direction and when you reverse to leads like a short in the other. What makes you think the BR is bad? If it was you wouldn't get good rail voltages or A/C along with low D/C on the rail.

 

[VSAT88]

The reason I checked it was because when I put it in one of the leads seemed a bit loose as I recall. I checked each lead with a little wiggle with needle nose pliers and all seems well. I just had my meter out and handy so I checked it. It does as you say on the 200 Ohm scale.

 

[Netfly]

So I read through this post and from what I see you problem is your getting good rail voltage, but high DC offset voltages at the speaker terminals. Are you measuring that DC from the + to the - speaker terminal of each channel separately, not to ground?

 

[VSAT88]

Yes. From positive and negative of the speaker leads. Not from positive speaker leads to ground.

 

[laatsch55]

A bridge rectifier is 4 separate diodes, ohms check will not tell you anything. Do you have a diode check mode on your meter??


When you put your negative lead on the buss bar what are your plus and minus readings on the output lugs of the filter caps??

 

[VSAT88]

Yes, I do have the diode setting on the meter. All seems well there. 31 VDC on the + rail. 21 VDC on the negative rail

 

[laatsch55]

At what mains voltage?? Rails on a 400 should be plus/minus 80vdc....