phase linear 400

[ABebar]

Ugh, I'm having trouble with my WOPL400 again. A few months back you guys (mostly Joe ) helped me out with a distorted right channel. I reflowed all of the 0.33 ohm resistors from the top of the backplane board and the problem went away. For a while. When it came back this time reflowing from the top did not do the trick, so I removed the transistors and resoldered the joints from the back. I must have cut these leads too much for fear of arcing to the chassis. I have a magnifying glass this time and was able to find a few sketchy connections that I thought could be the issue. I put it all back together, eased it up on the variac and now I have no B-/B+ rail voltage. Fuses are all fine and the dim bulb check is barely a soft orange glow at 110vac.
Frustrated for the night, but need to get it fixed. I sold all of my other amps and this is the only 2 channel I have.
Any suggestions on where to start?

 

[George S.]

Stop. Check the polarity of the big storage caps is correct.
The upper caps - goes to the buss bar.
The lower caps + goes to the buss bar.
Now. Check for rail voltage at these caps.
Negative lead of DMM on buss bar.
Positive lead of DMM on upper cap + should show +80VDC.
Then.
Positive lead of DMM on lower cap - should show -80VDC.
99% chance you have these voltages correct at this point.
So.
Keep the negative lead connected to the buss bar, ideally with a good clip, and start probing with the positive lead from the caps out to the back planes until you find the issue.

If. If you do have the storage cap polarity correct, but no rail voltage to them, then it's a issue with the power cord, main fuse, transformer wiring, or rectifier.
Careful. Lethal AC voltages here.

 

[George S.]

And, there are B+ and B- fuse holders on the later revision backplane boards.
My boards are early versions with no fuse holders, but are still fused.
Picofuses, they look like small green resistors.
Have to say, never had a issue with a WOPL that wasn't my fault. Rock solid design.
Here's my spare bag of pico for my 400 WOPLs earlier backplane boards.

 

[ABebar]

Oh, I'm 100% certain that I am at fault.
I have the newer backplane boards with fuse holders. When I was missing B-/B+ the first thing I did was power down and check the 7 glass fuses - three off of the transformer and two on each backplane. All checked good.
What's strange is that the amp has been working great for the better part of the past year - except for the intermittent right channel distortion. I only unmounted the control board and removed all 8 transistors from the right backplane to pull the board forward and touch up the 0.33 resistor solder points from the back, then reinstalled all at once and powered on slowly with variac and dbt. I didn't touch the caps or wiring. I was thinking that I may have overtightened a transistor and created a short to chassis through the silpad, but was fairly careful just to snug and not crank down, and would expect my dbt to be illuminated if I had a direct short.
I guess my plan tonight was to remove the chassis ground and check for shorts as described in the backplane bring-up instructions, but if I don't find any I'm at a loss of what to do next. I can power back on and try to follow the voltage from caps on down, and see when it drops.

 

[mlucitt]

If you are not blowing fuses, you don't have a short to ground. With no B+ or B- I would suspect a broken wire that is common to both rail sources. There are only a few. Follow George's troubleshooting steps above starting with AC power to the amplifier, you will find the issue in short order.

 

[gene french]

any more progress on the wopl??

 

[gene french]

well...just paid w0ad invoice...soon i can finish christine ....dont know why...because its there!!!
lololol

 

[ABebar]

I have been too embarrassed to tell you guys what I found when I got back home. I must have been exhausted on Thursday night, because I apparently had my meter set to AC.
(Facepalm)
All is well. I went home, verified +/- 80vdc, adjusted my bias, and hooked her back up. She sounds great. Again.

 

[gene french]

brain farts are not rare!!!

lolol

 

[Gepetto]

I have been too embarrassed to tell you guys what I found when I got back home. I must have been exhausted on Thursday night, because I apparently had my meter set to AC.
(Facepalm)
All is well. I went home, verified +/- 80vdc, adjusted my bias, and hooked her back up. She sounds great. Again.

You forgot rule number 1. It's your test equipment...

 

[gene french]

must have been a short between the fluke and the chair ....
lololol

 

[gene french]

ive done a lot worst!!!
lololol ..

 

[gene french]

I have been too embarrassed to tell you guys what I found when I got back home. I must have been exhausted on Thursday night, because I apparently had my meter set to AC.
(Facepalm)
All is well. I went home, verified +/- 80vdc, adjusted my bias, and hooked her back up. She sounds great. Again.

on a serious note...congratulations !!!!!

 

[gene french]

I have been too embarrassed to tell you guys what I found when I got back home. I must have been exhausted on Thursday night, because I apparently had my meter set to AC.
(Facepalm)
All is well. I went home, verified +/- 80vdc, adjusted my bias, and hooked her back up. She sounds great. Again.

on a serious note...congratulations

 

[Sunnbobb]

Hi gang, just checking in. I've had my hands full for the past month. I'm hopefully getting back to the operating table soon. I enjoyed catching up on missed posts. And that Coffee looks fab Gene!

 

[gene french]

Hi gang, just checking in. I've had my hands full for the past month. I'm hopefully getting back to the operating table soon. I enjoyed catching up on missed posts. And that Coffee looks fab Gene!

got a cup here with your name on it...
come see us!!!!

 

[Sunnbobb]

Watch out, you never know! lol

 

[gene french]

the porch lite is on!!!

 

[gene french]

well, this afternoon or tomorrow...
i need to start the wopl for christine...
pretty much got caught up in the rat killing department...
flushed the radiator and replaced the antifreeze about a month after the bypass hose failure...
which tested the hot motor shutdown sensor...
the water escaped so fast...that the temp did not rise...
the truck just quit...
a bit of searching found the busted hose....after the truck cranked when it cooled down...
i do like that old dodge...i try to keep it in excellent shape...
i will be buried in that thing...lol

 

[Vintage 700b]

well, this afternoon or tomorrow...
i need to start the wopl for christine...
pretty much got caught up in the rat killing department...
flushed the radiator and replaced the antifreeze about a month after the bypass hose failure...
which tested the hot motor shutdown sensor...
the water escaped so fast...that the temp did not rise...
the truck just quit...
a bit of searching found the busted hose....after the truck cranked when it cooled down...
i do like that old dodge...i try to keep it in excellent shape...
i will be buried in that thing...lol

You and that Dodge have been through a lot together Gene .