phase linear 400

[Sunnbobb]

lololol...
words ive never heard before...and certainly never again...
lololol...
i must admit this is a very nice forum...with quite a few very nice people willing to share their knowledge!!!

I didn't say Saint! hahaha

 

[Sunnbobb]

Dang it. false reading. Replacing the resistor did not fix the issue. Square one squared

 

[gene french]

diodes??

 

[Sunnbobb]

The part by part testing will resume this evening while watching NCAA basketball. For now, it's 60 degrees outside, and I have a 71 Norton Commando that needs some road time.

 

[gene french]

got two front panels left to refurbish...
waiting on led kit from joe for one...
the other came with bad meters...
i have found a reasonable replacement...
used edison filaments for light
reprinted the dials...
whittled on front cover...
getting there....

 

[gene french]

wow...got er done...
larry came over to help...
with the handles...etc

 

[gene french]

built a little board to handle the dc fpr lamps

 

[George S.]

Very nice!

 

[Sunnbobb]

3V bridge rectifier? Smarty pants! LOL

 

[gene french]

well, well....the light board from joe....
arrived in miami....
wont be too terribly long now...

 

[Sunnbobb]

Good going Gene. Did you go with white? PS I think I have this pl400 tamed after going through and replacing all the 10W resistors, and the .001 capacitor. I went ahead and installed the WA output relay, and the DBT has quit lighting up. My final challenge is the right channel has .350 bias, and the left has zero. I have a new set of MJ21196G coming, and I hope that solves that issue. Also waiting on a couple WO control boards for another PL400 and PL400II from Joe.

 

[gene french]

warm white...and congrats on the progress!!!
had a similar issue with christine....long story short....check bias transistors and associated wiring...

 

[Sunnbobb]

Well, I'm back, did you miss me? hahaha. So here is where I am at. The PL400 with PL14 board. I have now replaced the transistors with new 96's, (bottom row are 410's). My DC offset on both channels is almost undetectable. The Bias on the left channel is set at .360, however the right channel bias is at .550 and is not adjustable with the pot. The amp fires up, the output relay does it's job, and the tight channel (farthest from the transformer) R25 resistor slowly burns up. I takes a couple minutes, but eventually it gets super hot and smokes. I've replaced and the symptom remains the same. Anyone know what is causing too much voltage to that resistor? I traced the schematic, but don't see a clue.

 

[Gepetto]

Well, I'm back, did you miss me? hahaha. So here is where I am at. The PL400 with PL14 board. I have now replaced the transistors with new 96's, (bottom row are 410's). My DC offset on both channels is almost undetectable. The Bias on the left channel is set at .360, however the right channel bias is at .550 and is not adjustable with the pot. The amp fires up, the output relay does it's job, and the tight channel (farthest from the transformer) R25 resistor slowly burns up. I takes a couple minutes, but eventually it gets super hot and smokes. I've replaced and the symptom remains the same. Anyone know what is causing too much voltage to that resistor? I traced the schematic, but don't see a clue.

Please include a snippet of the schematic you are referencing for the R25 callout. PL has many schematics, none very consistent. We want to get to the heart of the matter without a wild goose chase. 0.550 bias is not a good situation. Likely caused by a defective Q7 or Q10 on the control board schematic.

 

[Sunnbobb]

here is the impacted R25. Thanks for the help!

 

[Gepetto]

here is the impacted R25. Thanks for the help!

R41, the 0.22 ohm resistor on the back wall may be open. You should check.

 

[Sunnbobb]

OK, R41 checks out at .21...

 

[Sunnbobb]

I swapped all the transistors from side to side, and there is no change. Also took bias readings from both 10ohm resistors on the right channel. The one closest to the end of the cabinet reads .550, the one on the other side reads .07. Neither respond to adjustment of the pot.

 

[Sunnbobb]

I replaced Q7 and Q10, the bias remains at .550 and r 25 is still getting hot as a pistol.

 

[mlucitt]

Did you replace the the 10 Ohm resistors (R38 and R39) on the backplane?
What is the voltage on R25? Is it positive or negative referenced to Ground?
Is you lift on leg of D12, does R2 still get hot?

The amplifier might be in a permanent state of "current limiting". If you remove the yellow wire on the control board for the Right channel, does the resistor still get hot?