So, here I go. Phase Linear 400

[VSAT88]

I feel like I am making a lot of mistakes. The voltage I am ramping up to on the veriac is 120 vac. The 31 VDC is on the negative rail. The 21 VDC is on the + rail. This rail (the positive) changes between 11 VDC up to 21 VDC as I ramp up the voltage. It does not stabilize. It changes at the same time with the left face plate meter. The left meter (Channel A on the front face plate) pegs all the way over to + 3 dB then back to the resting position over and over when I power up. I have never seen 80 V Dc on either rail. I do not know if it is helpful or not but I noticed that the bottom filter cap keeps its charge and the top one does not when I turn the power off.

 

[laatsch55]

No DBT in circuit correct??

 

[laatsch55]

Don't be insulted----but I HAVE to ask this question.....is the voltage on the negative rail negative?

 

[laatsch55]

I do not know if it is helpful or not but I noticed that the bottom filter cap keeps its charge and the top one does not when I turn the power off.

Makes sense, you have positive rail voltage all over in that amp....top cap is the positive rail cap...

 

[VSAT88]

Perhaps I misread but I thought you told me not to take the DBT out of circuit, to use it as we were working on a current issue/problem. Here is an image of how I am connecting the VOM to test the rails. The bottom cap is showing - voltage. The top cap is showing + voltage

 

[laatsch55]

Nope, you did not misunderstand me, just checking. Leave the DBT out this time and bring the amp up slowly, if it pops a fuse take it back down immediately...

 

[VSAT88]

Don't be insulted----but I HAVE to ask this question.....is the voltage on the negative rail negative?

Please ask anything and I mean anything. I will not be insulted. You are helping me beyond measure.

 

[VSAT88]

Nope, you did not misunderstand me, just checking. Leave the DBT out this time and bring the amp up slowly, if it pops a fuse take it back down immediately...

59 V on the negative rail then POP.. That was around 100 VAC. Checked the fuses and all three are blown.

 

[laatsch55]

Ok, if you are popping rail fuses....it was a rail fuse correct??, the problem is usually on the backplane somewhere. Check all outputs for a short or open...

 

[laatsch55]

Ah, I see you edited your post......all 3 eh? gonna have to think about that one...

 

[VSAT88]

Ok, if you are popping rail fuses....it was a rail fuse correct??, the problem is usually on the backplane somewhere. Check all outputs for a short or open...

All three fuses blew. So just to make sure I am reading you correctly I need to remove all the output devices to include the drivers on the bottom row and check each one for short or open.

 

[laatsch55]

Check your outputs anyway, gotta get some sleep but I'll check back as soos as I get up.....nite bud....

 

[VSAT88]

Ah, I see you edited your post......all 3 eh? gonna have to think about that one...

Sorry, I wont do it again (edit)

 

[laatsch55]

You do not need to remove them to check for short or open, follow the service manual instructions to do that....

 

[VSAT88]

Same here. Thanks again.

 

[laatsch55]

Sorry, I wont do it again (edit)

Well, it can get confusing, thanks...

 

[VSAT88]

Here I go again. these are the measurements I came up with when I used the service manual test for the OPT.

Collector to Emitter test

top left 006 009 no reading on 200 Ohm scale on all six right channel
middle 006 009
bottom 001 005

Base to Emitter test

top left 008 1.5 12.9 12.1
middle 008 1.6 13.6 12.2
bottom 002 1.2 13.6 12.2

Sorry about the formatting I did my best

 

[laatsch55]

What leads do you have where?

 

[VSAT88]

Negative lead on meter to the bus on both tests

 

[laatsch55]

3 I'm having trouble making sense of your figures. With the front of the amp facing you, and the transformer on your left, let's call the row next to the transformer as row 1, the next row 2 etc. Then, top to bottom.

What are the settings on your meter, ohm wise?